U.S. patent application number 11/867305 was filed with the patent office on 2011-11-03 for null-fill antenna, omni antenna, and radio communication equipment.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Norihiko Oomuro.
Application Number | 20110267232 11/867305 |
Document ID | / |
Family ID | 34980265 |
Filed Date | 2011-11-03 |
United States Patent
Application |
20110267232 |
Kind Code |
A1 |
Oomuro; Norihiko |
November 3, 2011 |
NULL-FILL ANTENNA, OMNI ANTENNA, AND RADIO COMMUNICATION
EQUIPMENT
Abstract
A wide-angle null-fill antenna with no null in the depression
angle range, an omni antenna using the same, and radio
communication equipment. A null-fill antenna comprises a first
antenna array including antenna elements arranged with a prescribed
point as the center, and a second antenna array having amplitude
characteristics substantially equal to those of the antenna
elements forming the first antenna array. The first antenna array
is excited so that the excitation amplitude distribution is to have
symmetry with respect to the prescribed point, while the excitation
phase distribution is to have point symmetry with respect to the
prescribed point. The phase center of the first antenna array is
substantially coincident with that of the second antenna array.
Inventors: |
Oomuro; Norihiko; (Tokyo,
JP) |
Assignee: |
NEC CORPORATION
Tokyo
JP
|
Family ID: |
34980265 |
Appl. No.: |
11/867305 |
Filed: |
October 4, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11178948 |
Jul 12, 2005 |
7652623 |
|
|
11867305 |
|
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Current U.S.
Class: |
342/360 ;
342/1 |
Current CPC
Class: |
H01Q 1/246 20130101;
H01Q 21/293 20130101; H01Q 21/22 20130101 |
Class at
Publication: |
342/360 ;
342/1 |
International
Class: |
H01Q 3/00 20060101
H01Q003/00; H01Q 17/00 20060101 H01Q017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 2004 |
JP |
205149/2004 |
Dec 17, 2004 |
JP |
365860/2004 |
Mar 3, 2005 |
JP |
059655/2005 |
Claims
1-25. (canceled)
26. A null-fill antenna comprising: a first antenna array including
antenna elements arranged to intersect a line passing through a
prescribed point at right angles; and a center antenna element with
an excitation amplitude substantially equal to or less than that of
the antenna elements forming the first antenna array; wherein: the
first antenna array is excited so that the excitation amplitude
distribution is to have line symmetry with respect to the line
passing through the prescribed point, while the excitation phase
distribution is to have point symmetry with respect to the line
passing through the prescribed point; and the phase center of the
first antenna array is substantially coincident with that of the
center antenna element.
27. The null-fill antenna claimed in claim 26, wherein the
excitation amplitude of the center antenna element is substantially
equal to or less than that of the antenna elements adjacent to the
phase center among those forming the first antenna array.
28. The null-fill antenna claimed in claim 26, wherein the
prescribed point is the phase center of the first antenna
array.
29. The null-fill antenna claimed in claim 26, wherein the first
antenna array is a two-dimensional array in which antenna elements
are arranged parallel to the line passing through the prescribed
point to form third antenna arrays, and the third antenna arrays
are arranged to intersect the line passing through the prescribed
point at right angles.
30. The null-fill antenna claimed in claim 26, wherein the first
antenna array includes slot antennas each having longitudinal sides
parallel to the line passing through the prescribed point, and the
slot antennas are arranged to intersect the line passing through
the prescribed point at right angles.
31. The null-fill antenna claimed in claim 26, wherein a dipole
antenna element is used as the center antenna element.
32. The null-fill antenna claimed in claim 26, wherein the center
antenna element is provided with an electromagnetic wave absorber
around it.
33. The null-fill antenna claimed in claim 32, wherein the
electromagnetic wave absorber has a length, in the direction of
arrangement of the antenna elements forming the first antenna
array, longer than the spacings between the phase center and
antenna elements adjacent thereto among those forming the first
antenna array.
34. The null-fill antenna claimed in claim 33, wherein the
electromagnetic wave absorber is set to surround the center antenna
element and extend to adjacent antenna elements among those forming
the first antenna array.
35. The null-fill antenna claimed in claim 26, wherein the center
antenna element is set so that the maximum radiation direction is
tilted along the direction of arrangement of the antenna elements
forming the first antenna array.
36. The null-fill antenna claimed in claim 26, wherein, among the
antenna elements forming the first antenna array, antenna elements
closest to the phase center are spaced apart by a distance more
than the spacing between other antenna elements.
37. The null-fill antenna claimed in claim 26, wherein the antenna
elements forming the first antenna array are arranged with unequal
spacing.
38. The null-fill antenna claimed in claim 26, wherein the center
antenna element is set in a position on the side of the direction
of electromagnetic wave radiation as compared to the first antenna
array.
39. The null-fill antenna claimed in claim 29, wherein, when one of
the antenna elements forming the third antenna arrays is placed at
the phase center of the first antenna array, the phase difference
between electromagnetic waves radiated from the center antenna
element and the third antenna arrays is within .+-.60 degrees.
40. The null-fill antenna claimed in claim 30, wherein, when one of
the slot antennas is placed at the phase center of the first
antenna array, the phase difference between electromagnetic waves
radiated from the center antenna element and the slot antennas is
within .+-.60 degrees.
41. The null-fill antenna claimed in claim 26, wherein the center
antenna element has directivity along the direction of arrangement
of the antenna elements forming the first antenna array.
42. The null-fill antenna claimed in claim 26, further comprising,
in place of the center antenna element, a second center antenna
element with an excitation amplitude larger than that of the
antenna elements forming the first antenna array, wherein the phase
center of the first antenna array is substantially coincident with
that of the second center antenna element.
43-57. (canceled)
58. The null fill antenna claimed in claim 26, wherein the null
fill antenna is provided in radio communication equipment.
59. The null fill antenna claimed in claim 58, wherein the
null-fill antenna is placed in a high position so that the first
antenna array is in the vertical direction.
60. The null fill antenna claimed in claim 58, wherein the
null-fill antenna is placed in a high position so that a substrate,
on which the first antenna array is formed, is substantially
horizontal, and electromagnetic waves are radiated in the nadir
direction.
61. The null fill antenna claimed in claim 58, wherein the
null-fill antenna is placed in a low position so that a substrate,
on which the first antenna array is formed, is tilted at a
prescribed angle with respect to the horizontal plane.
62. The null fill antenna claimed in claim 58, wherein the radio
communication equipment is base station equipment.
63. An omni antenna comprising: a plurality of null-fill antennas,
each of the null-fill antennas comprising a first antenna array
including antenna elements arranged to intersect a line passing
through a prescribed point at right angles, and a center antenna
element with an excitation amplitude substantially equal to or less
than that of the antenna elements forming the first antenna array,
wherein the first antenna array is excited so that the excitation
amplitude distribution is to have line symmetry with respect to the
line passing through the prescribed point, while the excitation
phase distribution is to have point symmetry with respect to the
line passing through the prescribed point, and wherein the phase
center of the first antenna array is substantially coincident with
that of the center antenna element, wherein the antennas are
arranged in a concentric circle so that electromagnetic waves are
radiated outward.
64. An omni antenna as claimed in claim 63, where in the omni
antenna is provided in radio communication equipment.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a wide-angle null-fill
antenna having wide directivity in the depression angle direction,
an omni antenna using the same, and radio communication equipment,
more particularly, to a wide-angle null-fill antenna with no
insensitive area or blind zone in the vicinity of the antenna, an
omni antenna, and radio communication equipment.
BACKGROUND OF THE INVENTION
[0002] In general, a base station or BTS (Base Transceiver Station)
antenna for mobile communication is placed in a high position such
as the top of a building, and electric waves emitted from the
antenna is received by mobile communication terminals on the
ground.
[0003] Such a BTS antenna is provided with directivity so that
mobile communication terminals on the ground receive electric waves
at the same reception or input level regardless of their
locations.
[0004] The BTS antenna forms a beam, e.g., cosecant squared beam
(without a null in a depression angle range of up to 45 degrees
from the horizontal plane) in the elevation plane, to cause
substantially uniform input electric field on the ground in a
predetermined depression angle range.
[0005] FIG. 1 is a diagram showing the construction of a
conventional cosecant squared beam antenna. In the cosecant squared
beam antenna, antenna elements are arrayed vertically, and
hereinafter a description will be made on the assumption that
antenna elements are arrayed vertically. In this construction, a
beam emitted from each antenna element is formed with flares to
achieve such directivity that electromagnetic waves are radiated
within a predetermined angle in the horizontal plane.
[0006] Besides, a plurality of the antenna elements are arranged in
a vertical linear array to form a beam in the vertical direction.
The amplitudes of the antenna elements 2 or the upper half of the
array and the antenna elements 3 or the lower half of the array are
symmetrical about the center (e.g., the amplitude of the top
antenna element is the same as that of the bottom one). The phases
of all the antenna elements 2 are identical. Similarly, the phases
of all the antenna elements 3 are identical. The phase of the
antenna elements 2 is shifted with respect to that of the antenna
elements 3 by a prescribed amount.
[0007] With this construction, the antenna radiation pattern
assumes a cosecant squared pattern in the vertical plane, resulting
in substantially uniform input level in a range of depression angle
from the horizontal plane.
[0008] However, if a beam is formed in this manner, as shown in
FIG. 2, in an area at a depression angle over 45 degrees from the
horizontal plane with respect to the BTS antenna, i.e., around the
foot of the antenna, the input level is necessarily reduced.
[0009] FIG. 3 is a diagram showing the phase characteristics of the
conventional cosecant squared beam antenna. The phase
characteristics indicates the relation between angles and phases in
the vertical plane at points equally distant from the origin as an
observation point at the center of the array.
[0010] Referring to FIG. 3, in an area lower than the horizontal
plane or in an area at a depression angle of 0 (zero) degrees or
more, the phase is at 0 degrees. On the other hand, in an area at a
depression angle less than 0 degrees or in an area at an elevation
angle, the phase is at 180 degrees at almost all angles. This means
that, with the horizontal plane as a boundary face or an interface,
electromagnetic waves radiated to below the horizontal plane and
those radiated to above the horizontal plane are in phase
opposition.
[0011] FIG. 4 is a diagram showing the radiation or directivity
characteristics of the conventional cosecant squared beam antenna
in the vertical plane. In FIG. 4, in an area at a depression angle
of 45 degrees or more, the radiation characteristics deteriorate.
That is, an area in the vicinity of the antenna, at a depression
angle of not less than 45 degrees, involves a null.
[0012] In Japanese Patent Application laid open No. HEI9-246859,
there has been disclosed "Antenna" as a conventional technique for
improving the radiation characteristics in the vicinity of the
antenna. In the conventional technique, an array antenna consists
of a first antenna element with wide directivity in the zenith
direction and second antenna elements with narrow directivity in a
direction at a prescribed angle from the zenith direction, which
are arranged around the first antenna element. Thus, the input
level of mobile terminals is maintained constant.
[0013] However, the conventional technique is aimed at reducing
nulls caused in the direction of the front of the antenna for a
campus base station. Therefore, if the technique is applied to a
base station for mobile communication, the gain of the antenna is
significantly reduced in the direction at a depression angle of 90
degrees.
[0014] As just described, there has not been proposed a wide-angle
null-fill antenna preventing a null or the presence of an
insensitive area in the direction at a depression angle of 90
degrees.
SUMMARY OF THE INVENTION
[0015] It is therefore an object of the present invention to
provide a wide-angle null-fill antenna permitting little decrease
in reception or input level in the vicinity of the foot of the
antenna, an omni antenna using the same, and radio communication
equipment.
[0016] In accordance with the first aspect of the present
invention, to achieve the object mentioned above, there is provided
a null-fill antenna comprising a first antenna array including
antenna elements arranged with a prescribed point as the center,
and a second antenna array with an excitation amplitude
substantially equal to or less than that of the antenna elements
forming the first antenna array. The first antenna array is excited
so that the excitation amplitude distribution is to have symmetry
with respect to the prescribed point, while the excitation phase
distribution is to have substantially point symmetry with respect
to the prescribed point. The phase center of the first antenna
array is substantially coincident with that of the second antenna
array.
[0017] Preferably, in the null-fill antenna of the first aspect,
the excitation amplitude of the second antenna array is
substantially equal to or less than that of the antenna elements
adjacent to the phase center among those forming the first antenna
array.
[0018] Preferably, in the null-fill antenna of the first aspect,
the prescribed point is the phase center of the first antenna
array. Besides, the second antenna array includes at least two
antenna elements, and the antenna element closer to the phase
center is provided with larger excitation amplitude.
[0019] Preferably, in the null-fill antenna of the first aspect,
the antenna elements forming the second antenna array are arranged
in a line with the phase center as the center to intersect the
first antenna array as the axis of symmetry at right angles.
[0020] Preferably, in the null-fill antenna of the first aspect,
the antenna elements forming the second antenna array are arranged
not to overlap the phase center of the first antenna array.
[0021] Preferably, in the null-fill antenna of the first aspect,
dipole antennas are used as the antenna elements forming the second
antenna array. More preferably, each of the antenna elements
forming the second antenna array is provided with an
electromagnetic wave absorber around it. The electromagnetic wave
absorber may be arranged along the direction of arrangement of the
antenna elements forming the first antenna array with each of the
antenna elements forming the second antenna array as the center. In
addition, the electromagnetic wave absorber may have a length, in
the direction of arrangement of the antenna elements forming the
first antenna array, longer than the spacings between the phase
center and antenna elements adjacent thereto among those forming
the first antenna array.
[0022] Preferably, in the null-fill antenna of the first aspect,
the antenna elements forming the second antenna array are arranged
so that the maximum radiation direction of the second antenna array
is tilted along the direction of arrangement of the antenna
elements forming the first antenna array.
[0023] Among the antenna elements forming the first antenna array,
antenna elements closest to the phase center may be spaced apart by
a distance more than the spacing between other antenna elements.
The antenna elements forming the first antenna array may be
arranged with unequal spacing.
[0024] The null-fill antenna of the first aspect may further
comprise, in place of the second antenna array, a third antenna
array with an excitation amplitude larger than that of the antenna
elements forming the first antenna array, the phase center of which
is substantially coincident with that of the first antenna
array.
[0025] The null-fill antenna of the first aspect may further
comprise, in place of the second antenna array, a slot antenna or a
dipole antenna with an excitation amplitude substantially equal to
or less than that of the antenna elements forming the first antenna
array, the phase center of which is substantially coincident with
that of the first antenna array.
[0026] The null-fill antenna of the first aspect may further
comprise, in place of the second antenna array, a parasitic element
which is spaced a prescribed distance apart from the phase center
of the first antenna array in the vertical direction with respect
to the first antenna array.
[0027] Preferably, in the null-fill antenna of the first aspect,
the excitation amplitude of the second antenna array, the slot
antenna, the dipole antenna or the parasitic element is less than
that of the antenna elements adjacent to the phase center of the
first antenna array among those forming the first antenna
array.
[0028] Preferably, in the null-fill antenna of the first aspect,
when one of the antenna elements forming the first antenna array is
placed at the phase center of the first antenna array, the phase
difference between electromagnetic waves radiated from the antenna
element and the second antenna array, the slot antenna, the dipole
antenna or the parasitic element is within .+-.60 degrees.
[0029] The second antenna array, the slot antenna, the dipole
antenna or the parasitic element may have directivity along the
direction of arrangement of the antenna elements forming the first
antenna array.
[0030] The null-fill antenna of the first aspect may further
comprise, in place of the slot antenna or the dipole antenna, a
second slot antenna or a second dipole antenna with an excitation
amplitude larger than that of the antenna elements forming the
first antenna array, the phase center of which is substantially
coincident with that of the first antenna array.
[0031] In accordance with the second aspect of the present
invention, to achieve the object mentioned above, there is provided
a null-fill antenna comprising a first antenna array including
antenna elements arranged to intersect a line passing through a
prescribed point at right angles, and a center antenna element with
an excitation amplitude substantially equal to or less than that of
the antenna elements forming the first antenna array. The first
antenna array is excited so that the excitation amplitude
distribution is to have line symmetry with respect to the line
passing through the prescribed point, while the excitation phase
distribution is to have point symmetry with respect to the line
passing through the prescribed point. The phase center of the first
antenna array is substantially coincident with that of the center
antenna element.
[0032] Preferably, in the null-fill antenna of the second aspect,
the excitation amplitude of the center antenna element is
substantially equal to or less than that of the antenna elements
adjacent to the phase center among those forming the first antenna
array.
[0033] Preferably, in the null-fill antenna of the second aspect,
the prescribed point is the phase center of the first antenna
array.
[0034] The first antenna array may be a two-dimensional array in
which antenna elements are arranged parallel to the line passing
through the prescribed point to form third antenna arrays, and the
third antenna arrays are arranged to intersect the line passing
through the prescribed point at right angles.
[0035] The first antenna array may include slot antennas each
having longitudinal sides parallel to the line passing through the
prescribed point, which are arranged to intersect the line passing
through the prescribed point at right angles.
[0036] Preferably, in the null-fill antenna of the second aspect, a
dipole antenna element is used as the center antenna element. More
preferably, the center antenna element is provided with an
electromagnetic wave absorber around it. The electromagnetic wave
absorber may have a length, in the direction of arrangement of the
antenna elements forming the first antenna array, longer than the
spacings between the phase center and antenna elements adjacent
thereto among those forming the first antenna array. In addition,
the electromagnetic wave absorber may be set to surround the center
antenna element and extend to adjacent antenna elements among those
forming the first antenna array.
[0037] Preferably, in the null-fill antenna of the second aspect,
the center antenna element is set so that the maximum radiation
direction is tilted along the direction of arrangement of the
antenna elements forming the first antenna array.
[0038] Among the antenna elements forming the first antenna array,
antenna elements closest to the phase center may be spaced apart by
a distance more than the spacing between other antenna elements.
The antenna elements forming the first antenna array may be
arranged with unequal spacing.
[0039] Preferably, in the null-fill antenna of the second aspect,
the center antenna element is set in a position on the side of the
direction of electromagnetic wave radiation as compared to the
first antenna array.
[0040] Preferably, in the null-fill antenna of the second aspect,
when one of the antenna elements forming the third antenna arrays
or slot antennas is placed at the phase center of the first antenna
array, the phase difference between electromagnetic waves radiated
from the center antenna element and the third antenna arrays or the
slot antennas is within .+-.60 degrees.
[0041] Preferably, in the null-fill antenna of the second aspect,
the center antenna element has directivity along the direction of
arrangement of the antenna elements forming the first antenna
array.
[0042] The null-fill antenna of the second aspect may further
comprise, in place of the center antenna element, a second center
antenna element with an excitation amplitude larger than that of
the antenna elements forming the first antenna array, the phase
center of which is substantially coincident with that of the first
antenna array.
[0043] Preferably, in the null-fill antenna of the first or second
aspect, the maximum radiation direction of the first antenna array
is tilted along the direction of arrangement of the antenna
elements forming the first antenna array. More preferably, the
maximum radiation direction of at least antenna elements in the
vicinity of the center among those forming the first antenna array
are tilted along the direction of arrangement of the antenna
elements, in the maximum radiation direction of the first antenna
array.
[0044] Preferably, in the null-fill antenna of the first or second
aspect, among the antenna elements forming the first antenna array,
antenna elements on one side of the phase center are advanced more
in excitation phase as the distance from the phase center
increases, while antenna elements on the other side of the phase
center are delayed more in excitation phase as the distance from
the phase center increases.
[0045] Preferably, in the null-fill antenna of the first or second
aspect, each of the antenna elements forming the first antenna
array is provided with a parasitic element.
[0046] An indirectly excited element, which is excited by radiation
from the first antenna array, may be used as an antenna element
added to the center.
[0047] Preferably, in the null-fill antenna of the first or second
aspect, a substrate, on which the first antenna array is formed, is
provided with flares on both sides thereof in the direction of
arrangement of the antenna elements forming the first antenna
array.
[0048] Preferably, in the null-fill antenna of the first or second
aspect, the null-fill antenna is a wide-angle null-fill
antenna.
[0049] Preferably, in the null-fill antenna of the first or second
aspect, the first antenna array has cosecant squared pattern
directivity in the direction of arrangement of the antenna
elements.
[0050] In accordance with the third aspect of the present
invention, to achieve the object mentioned above, there is provided
radio communication equipment provided with the null-fill antenna
of the first or second aspect.
[0051] Preferably, in the radio communication equipment of the
third aspect, the null-fill antenna is placed in a high position so
that the first antenna array is in the vertical direction. Or the
null-fill antenna is placed in a high position so that a substrate,
on which the first antenna array is formed, is substantia
horizontal, and electromagnetic waves are radiated in the nadir
direction. The null-fill antenna may be placed in a low position so
that a substrate, on which the first antenna array is formed, is
tilted at a prescribed angle with respect to the horizontal
plane.
[0052] In accordance with the fourth aspect of the present
invention, to achieve the object mentioned above, there is provided
an omni antenna comprising a plurality of the null-fill antennas of
the first or second aspect, in which the null-fill antennas are
arranged in a concentric circle so that electromagnetic waves are
radiated outward.
[0053] In accordance with the fifth aspect of the present
invention, to achieve the object mentioned above, there is provided
radio communication equipment provided with the omni antenna of the
fourth aspect.
[0054] The radio communication equipment may be base station
equipment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] The objects and features of the present invention will
become more apparent from the consideration of the following
detailed description taken in conjunction with the accompanying
drawings in which:
[0056] FIG. 1 is a diagram showing the construction of a
conventional cosecant squared beam antenna;
[0057] FIG. 2 is a diagram showing the insensitive area of a
conventional base station;
[0058] FIG. 3 is a diagram showing the phase characteristics of the
conventional cosecant squared beam antenna;
[0059] FIG. 4 is a diagram showing the vertical directivity
characteristics of the conventional cosecant squared beam
antenna;
[0060] FIG. 5 is a diagram showing the amplitude distribution and
phase distribution of respective antenna elements included in a
wide-angle null-fill antenna of the present invention;
[0061] FIG. 6 is a diagram showing the vertical directivity
characteristics of the wide-angle null-fill antenna of the present
invention;
[0062] FIG. 7 is a diagram showing the construction of a wide-angle
null-fill antenna according to the first embodiment of the present
invention;
[0063] FIG. 8 is a diagram showing the directivity characteristics
of an antenna array added to the vicinity of the phase center of
the wide-angle null-fill antenna depicted in FIG. 7;
[0064] FIG. 9 is a diagram showing phase differences between
electromagnetic waves observed at points equally distant from the
phase center when an antenna element is added to the phase
center;
[0065] FIG. 10 is a diagram showing phase differences between
electromagnetic waves observed at points equally distant from the
phase center when an antenna array is added to the vicinity of the
phase center;
[0066] FIG. 11 is a diagram showing the radiation pattern phase
characteristics of an antenna array added to the vicinity of the
phase center of the wide-angle null-fill antenna depicted in FIG. 7
in the horizontal plane;
[0067] FIG. 12 is a diagram showing the vertical directivity
characteristics of the wide-angle null-fill antenna when the phase
of each antenna element in an antenna array added to the vicinity
of the phase center is shifted by 0 degrees;
[0068] FIG. 13 is a diagram showing the vertical directivity
characteristics of the wide-angle null-fill antenna when the phase
of each antenna element in an antenna array added to the vicinity
of the phase center is shifted by .+-.60 degrees;
[0069] FIG. 14 is a diagram showing the vertical directivity
characteristics of the wide-angle null-fill antenna when the phase
of each antenna element in an antenna array added to the vicinity
of the phase center is reversed;
[0070] FIG. 15 is a diagram showing the insensitive area of a base
station of the present invention;
[0071] FIG. 16 is a diagram showing the amplitude distribution,
phase distribution and vertical directivity characteristics of an
antenna element when the antenna is set in a tilted position;
[0072] FIG. 17 is a diagram showing the construction of a
wide-angle null-fill antenna according to the second embodiment of
the present invention;
[0073] FIG. 18 is a diagram showing the side view of the vicinity
of the phase center of the wide-angle null-fill antenna depicted in
FIG. 17;
[0074] FIG. 19 is a diagram showing the maximum radiation direction
of electromagnetic waves when a dipole antenna is set so that the
dipoles are vertically oriented;
[0075] FIG. 20 is a diagram showing the maximum radiation direction
of electromagnetic waves when a dipole antenna is set so that the
dipoles are oriented at a depression angle with respect to the
vertical direction;
[0076] FIG. 21 is a diagram showing the construction of a
wide-angle null-fill antenna according to the third embodiment of
the present invention;
[0077] FIG. 22 is a diagram showing the internal construction of
the substrate of the wide-angle null-fill antenna depicted in FIG.
21;
[0078] FIG. 23 is a diagram showing a base station provided with
the wide-angle null-fill antenna depicted in FIG. 21 whose maximum
radiation direction is tilted at a descending vertical angle;
[0079] FIG. 24 is a diagram showing the excitation amplitude and
excitation phase distributions of the wide-angle null-fill antenna
depicted in FIG. 21 whose maximum radiation direction is tilted
downward;
[0080] FIG. 25 is a diagram showing the radiation pattern of the
wide-angle null-fill antenna depicted in FIG. 21 whose maximum
radiation direction is tilted downward;
[0081] FIG. 26 is a diagram showing the construction of a
wide-angle null-fill antenna according to the fourth embodiment of
the present invention;
[0082] FIG. 27 is a diagram showing the construction of a
wide-angle null-fill antenna in which each of rectangular patch
antenna elements in an array is provided with a rectangular
parasitic element;
[0083] FIG. 28 is a diagram showing an example of the construction
of a wide-angle null-fill antenna according to the fifth embodiment
of the present invention;
[0084] FIG. 29 is a diagram showing another example of the
construction of a wide-angle null-fill antenna according to the
fifth embodiment of the present invention;
[0085] FIG. 30 is a diagram showing the construction of a
wide-angle null-fill antenna according to the sixth embodiment of
the present invention;
[0086] FIG. 31 is a diagram showing the side view of the vicinity
of the phase center of the wide-angle null-fill antenna depicted in
FIG. 30;
[0087] FIG. 32 is a diagram showing the construction of a
wide-angle null-fill antenna according to the seventh embodiment of
the present invention;
[0088] FIG. 33 is a diagram showing the side view of the vicinity
of the phase center of the wide-angle null-fill antenna depicted in
FIG. 32;
[0089] FIG. 34 is a diagram showing the construction of a
wide-angle null-fill antenna in which a patch antenna element added
to the phase center is tilted at an depression angle, and also,
among patch antenna elements in an antenna array, those on both
sides of the antenna element added to the phase center are tilted
at an depression angle;
[0090] FIG. 35 is a diagram showing the construction of a
wide-angle null-fill antenna according to the eighth embodiment of
the present invention;
[0091] FIG. 36 is a diagram showing the side view of the vicinity
of the phase center of the wide-angle null-fill antenna depicted in
FIG. 35;
[0092] FIG. 37 is a diagram showing the construction of a
wide-angle null-fill antenna according to the ninth embodiment of
the present invention;
[0093] FIG. 38 is a diagram showing the side view of the vicinity
of the phase center of the wide-angle null-fill antenna depicted in
FIG. 37;
[0094] FIG. 39 is a diagram showing excitation amplitude and
excitation phase distributions when the beam peak is set at a
depression angle of 30 degrees;
[0095] FIG. 40 is a diagram showing the radiation pattern when the
beam peak is at a depression angle of 30 degrees;
[0096] FIG. 41 is a diagram showing radiation characteristics in a
remote area;
[0097] FIG. 42 is a diagram showing the construction of a
wide-angle null-fill antenna which is provided with metal flare
plates on both sides of antenna elements to form a beam in the
horizontal plane;
[0098] FIG. 43 is a diagram showing the construction of a
wide-angle null-fill antenna in which a parasitic V-shaped dipole
element is used as an antenna element added to the phase center and
excited not directly but indirectly via air by radiation waves from
an antenna array;
[0099] FIG. 44 is a diagram showing the construction of an omni
antenna according to the tenth embodiment of the present
invention;
[0100] FIG. 45 is a diagram showing the construction of base
station equipment according to the eleventh embodiment of the
present invention; and
[0101] FIG. 46 is a diagram showing the construction of base
station equipment according to the twelfth embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0102] Studies by the inventor has shown that, in a cosecant
squared beam antenna including antenna elements of the same
characteristics arrayed with equal spacing therebetween, the
radiation characteristics of the antenna is improved in a directly
downward direction when an antenna element is added to the phase
center.
[0103] FIG. 5 is a diagram showing the amplitude and phase
distributions of respective antenna elements when an antenna
element is added to the phase center. The amplitude of the newly
added antenna element is small (-5 dB in this example) as compared
to that of antenna elements on both sides (those at positions
spaced 0.35 wavelength apart from the phase center). The newly
added antenna element is provided with a smaller amplitude than
those on both sides to prevent a decrease in peak gain.
[0104] FIG. 6 is a diagram showing the directivity characteristics
of the antenna in the vertical plane. When an antenna element is
added to the phase center of a cosecant squared beam antenna and
excited following the above conditions, the amplitude decreases in
the elevation angle range, while it increases in the depression
angle range. The antenna characteristics are improved in the
vicinity of a depression angle of 90 degrees. Besides, in the
depression angle range, variation (i.e., ripple) in the input
electric field or voltage decreases, which allows receivers to
receive electromagnetic waves stably.
[0105] In a cosecant squared beam antenna, however, antenna
elements are arrayed with, e.g., 0.7 wavelength spacing, and they
have a size or length of 0.35 to 0.5 wavelength. That is, if an
antenna element is newly added to the phase center, the antenna
element physically interferes or contacts with those adjacent to
it. In other words, it is physically impossible to add an extra
antenna element to the phase center of a cosecant squared beam
antenna.
[0106] Therefore, in accordance with the present invention, one or
more antenna elements are arranged in the vicinity of the phase
center which have characteristics equivalent to those of antenna
elements forming a cosecant squared beam antenna as well as making
no physical interference with them. Thus, a null does not occur in
the depression angle direction of the cosecant squared beam
antenna.
[0107] Based on the principles described above, a description of
preferred embodiments of the present invention will be given
referring to the drawings.
First Embodiment
[0108] FIG. 7 is a diagram showing the construction of a wide-angle
null-fill antenna according to the first embodiment of the present
invention. As can be seen in FIG. 7, the wide-angle null-fill
antenna comprises a substrate 1 and antenna elements 2 and 3
arrayed at regular intervals on the surface of the substrate 1. The
antenna elements 2 are arranged with an equal spacing of 0.7.lamda.
(.lamda.: the wavelength of electromagnetic waves radiated
therefrom) from a position 0.35.lamda. apart from the phase center
in the zenith direction. On the other hand, the antenna elements 3
are arranged with an equal spacing of 0.7.lamda. from a position
0.35.lamda. apart from the phase center in the nadir direction. The
substrate 1 is provided with flares 4 on both sides thereof in the
longitudinal direction (the direction of arrangement of the antenna
elements 2 and 3). Incidentally, all the antenna elements 2 and 3
have the same characteristics.
[0109] The wide-angle null-fill antenna further comprises an
antenna array 5 on the substrate 1, in the same horizontal plane as
the phase center. The antenna array 5 includes four antenna
elements arranged at regular intervals with the phase center in the
center of them. More specifically, on both sides of the phase
center, two of the four antenna elements are placed at 0.35.lamda.
spacing from the phase center, and the other two are placed at
1.05.lamda. spacing from the phase center in the horizontal plane
of the substrate 1.
[0110] The antenna array 5 has radiation characteristics equivalent
to those of the antenna elements 2 and 3.
[0111] Among the additional four antenna elements of the antenna
array 5, inner two antenna elements (closer to the phase center)
are delayed 30 degrees in phase and have an amplitude of -10 dB as
compared to one of the antenna elements 2 closest to the phase
center. Besides, outer two antenna elements (more distant from the
phase center) are advanced 120 degrees in phase and have an
amplitude of -6 dB as compared to the inner two.
[0112] The antenna elements 3 (on the lower side) are delayed 60
degrees in phase as compared to the antenna elements 2 (on the
upper side). More specifically, assuming that the inner two antenna
elements of the antenna array 5 have a phase of 0 degrees, the
antenna elements 2 are advanced 30 degrees in phase, while the
antenna elements 3 are delayed 30 degrees in phase as compared to
the inner two elements.
[0113] FIG. 8 is a diagram showing the radiation characteristics of
the wide-angle null-fill antenna. In FIG. 8, "ELEMENT" indicates
the radiation characteristics of the antenna element, "ARRAY"
indicates the radiation characteristics (array factor) determined
by the arrangement of antenna elements, and "TOTAL" indicates the
integration of them, i.e., the radiation characteristics of the
antenna as a whole. Incidentally, the three types of radiation
characteristics are defined by the relation
ELEMENT.times.ARRAY=TOTAL. That is, if the array factor is flat
(=1), the radiation characteristics of the antenna as a whole
corresponds to those of the antenna element.
[0114] In this case, in a required angle range (e.g., an angle
range of .+-.30 degrees when the antenna is used as an omni antenna
consisting of six sectors), if the array factor shows substantially
flat characteristics, the antenna array 5 can be considered to have
the same radiation characteristics as those of the antenna elements
2 and 3. In other words, the antenna array 5 is equivalent to an
antenna element that is added to the phase center. Accordingly, it
is possible to achieve such effects as to increase the amplitude of
electromagnetic waves radiated in the depression angle direction
and to reduce that of electromagnetic waves radiated in the
elevation angle direction.
[0115] However, even if the antenna array 5 radiates
electromagnetic waves of the same amplitude as in the case of an
antenna element added to the phase center, actually, the phase of
electromagnetic waves radiated from the antenna array 5 differs
from that in the case where an antenna element is added to the
phase center.
[0116] FIGS. 9 and 10 are diagrams schematically showing the
relation between a point at which electromagnetic waves radiated
from the antenna are observed and the phase of electromagnetic
waves observed at the point, when an antenna element is placed in
the phase center and when an antenna array is arranged in the
vicinity of the phase center, respectively. In FIG. 10, the heavy
dotted line indicates phase shifts when electromagnetic waves
radiated from the antenna are observed at points on the thin dotted
line equally distant from the phase center in the horizontal plane.
At the points where the heavy dotted line comes close to the phase
center as compared to the thin dotted line, electromagnetic waves
with a phase shifted to the minus side are observed. At the points
where the heavy dotted line comes away from the phase center as
compared to the thin dotted line, electromagnetic waves with a
phase shifted to the plus side are observed. As can be seen in FIG.
9, when an antenna element is placed at the phase center, the
phases of observed electromagnetic waves radiated from the antenna
element are identical at all points equally distant from the phase
center. On the other hand, as can be seen in FIG. 10, when an
antenna array is placed, even at points equally distant from the
phase center, the phases of observed electromagnetic waves radiated
from the antenna array vary depending on the points.
[0117] FIG. 11 is a diagram showing the directivity characteristics
of the antenna array 5. As shown in FIG. 11, in an angle range of
.+-.30 degrees in the horizontal direction, the phase varies
approximately .+-.30 degrees.
[0118] The effect of the phase variation will be described by
referring to FIGS. 12 to 14. FIGS. 12 to 14 are diagrams showing
the directivity characteristics of the wide-angle null-fill antenna
when the phase of the antenna array 5 is shifted by 0 degrees
(i.e., without a shift), when it is shifted by .+-.60 degrees, and
when it is shifted by 180 degrees (i.e., phase-reversed),
respectively. When the phase is not shifted, electromagnetic waves
radiated in the elevation angle direction are weakened, while those
radiated in the depression angle direction are reinforced. In the
case where the phase of the antenna array 5 is shifted by .+-.60
degrees, although not as significant as in the case of no phase
shift, electromagnetic waves radiated in the elevation angle
direction are weakened, while those radiated in the depression
angle direction are reinforced. Besides, if the phase of the
antenna array 5 is reversed, similar effects are not shown.
Incidentally, in FIGS. 12 to 14, the directivity characteristics
are shown on the assumption of a sector of 60 degrees and no array
factor within the range.
[0119] As just described, even though the phase of electromagnetic
waves radiated from the antenna array 5 is not completely the same
as in the case where an antenna element is added to the phase
center, it is possible to sufficiently achieve the effects of
weakening electromagnetic waves radiated in the elevation angle
direction as well as reinforcing electromagnetic waves radiated in
the depression angle direction. In practical use, if the phase is
shifted to the extent of approximately .+-.60 degrees, the
aforementioned effects can be sufficiently achieved.
[0120] In this example, the antenna array 5 has no directivity in
the vertical plane or the direction of arrangement of the antenna
elements 2 and 3. However, the antenna array 5 may have vertical
directivity. When the radiation characteristics of the antenna
array 5 include directivity in the depression angle direction, the
electric field strength can be further improved in the area
directly below the antenna (in the vicinity of a depression angle
of 90 degrees).
[0121] As is described above, according to the first embodiment of
the present invention, the wide-angle null-fill antenna is capable
of enhancing the input electric field in the area around the
antenna where the depression angle is large. Therefore, when the
wide-angle null-fill antenna is used as a base station or BTS (Base
Transceiver Station) antenna, there is formed no insensitive area
around the foot of the antenna.
[0122] Besides, the antenna array 5 increases the electric field at
substantially the same level with respect to all directions.
Thereby, the ripple can be minimized.
[0123] Further, the phase of sidelobes emitted in the zenith
direction is opposite to that of electromagnetic waves radiated in
the depression angle direction. Consequently, the antenna array 5
can reduce the sidelobes in the zenith direction, and a strong beam
is not to be emitted in an undesired direction.
[0124] In the first embodiment, as shown in FIG. 7, the antenna
array 5 includes four antenna elements, which are regularly spaced
with the phase center therebetween. However, the number of antenna
elements is given only as an example, and the antenna array 5 may
include two or six elements. That is, the antenna array may be
composed of 2n (n: an arbitrary positive integer) antenna elements.
Additionally, while the antenna elements 2 and 3 are arranged in a
linear array, they may be arranged in a plurality of arrays, e.g.,
three arrays, to form a matrix, with the antenna array 5 at the
phase center.
[0125] Further, in the above description, the horizontal radiation
directivity is almost 0 degrees. However, the maximum radiation
direction may be tilted in the vertical plane with the same
advantages. The maximum radiation direction can be tilted by
providing tilt to only the excitation phase characteristics without
changing the excitation amplitude characteristics. In the
wide-angle null-fill antenna of this embodiment, if the antenna
elements 2 are advanced more in phase as the distance from the
phase center increases, while the antenna elements 3 are delayed
more in phase as the distance from the phase center increases, the
maximum radiation direction can be tilted at a depression angle.
FIG. 16 is a diagram showing the amplitude distribution, phase
distribution and vertical directivity characteristics of the
wide-angle null-fill antenna tilted at a depression angle. The
vertical directivity characteristics indicate that the beam peak is
at a depression angle of 15 degrees. In this manner, when a beam is
tilted downward, interference (overreach) to adjacent cells can be
reduced. Thus, the wide-angle null-fill antenna can be effectively
used as a BTS antenna when small cells are desired.
Second Embodiment
[0126] FIG. 17 is a diagram showing the construction of a
wide-angle null-fill antenna according to the second embodiment of
the present invention. As can be seen in FIG. 17, the wide-angle
null-fill antenna of this embodiment is basically similar in
construction and general arrangement to that of the first
embodiment. The wide-angle null-fill antenna comprises a substrate
1 and a total of 14 patch antenna elements 2 and 3. On the
substrate 1, the patch antenna elements 2 and 3 are arranged
vertically to form a linear first antenna array. In FIG. 17, a
crisscross () mark indicates the phase center of the first antenna
array. The wide-angle null-fill antenna further comprises two
dipole antennas 10 as a second antenna array with the phase center
of the first antenna array between them. That is, the phase centers
of the first and second arrays are located at the same position.
The dipoles are oriented parallel to the first antenna array.
[0127] FIG. 18 is a diagram showing the enlarged side view of the
vicinity of the phase center of the wide-angle null-fill antenna.
Although a single dipole antenna 10 is omnidirectional in the
horizontal plane, a combination of the two in an array can narrow
down the beamwidth in the horizontal plane. In addition, since a
dipole antenna has weak directivity and is susceptible to the
effect of a reflector plate, each of the dipole antennas 10 is
provided with an electromagnetic wave absorber 11 to reduce the
frequency characteristics of the beamwidth in the horizontal plane.
As can be seen in FIGS. 17 and 18, the electromagnetic wave
absorbers 11 are set around the two dipole antennas 10,
respectively, with the supporting portion of the antenna as the
center.
[0128] According to the second embodiment, the electromagnetic wave
absorber 11 is arranged so as to surround the supporting portion of
the dipole antenna 10 and extend to two patch antenna elements
adjacent to the antenna 10. In other words, the electromagnetic
wave absorber 11 is set to surround the center antenna element, and
also extended in the horizontal direction (the direction of
arrangement of the patch antenna elements 2 and 3 forming the first
antenna array). With this construction, it is possible to reduce
the frequency characteristics of the beamwidth in the horizontal
plane as well as to increase the electric field level on the ground
in the vertical plane.
[0129] FIG. 19 is a diagram showing the maximum radiation direction
of electromagnetic waves when the dipole antenna 10 is vertically
oriented. FIG. 20 is a diagram showing the maximum radiation
direction of electromagnetic waves when the dipole antenna 10 is
oriented at a depression angle with respect to the vertical
direction. In FIG. 20, the dotted line indicates the radiation
characteristics of the wide-angle null-fill antenna. As shown in
FIG. 19, the vertical orientation of the dipole antenna 10 results
in the horizontal maximum radiation direction. On the other hand,
as shown in FIG. 20, the dipole antenna 10 oriented at an angle
(depression angle) with respect to the vertical direction causes
the maximum radiation direction to be downward with respect to the
horizontal direction. When the dipole antenna 10 is oriented
downwardly, the radiation level to which the center antenna element
contributes increases in the wide-depression angle direction. As a
result, the wide-angle null-fill antenna hardly forms a null at the
foot of the antenna.
Third Embodiment
[0130] FIG. 21 is a diagram showing the construction of a
wide-angle null-fill antenna according to the third embodiment of
the present invention. Referring to FIG. 21, the wide-angle
null-fill antenna comprises a substrate 1 and antenna elements 2
and 3 arrayed at regular intervals on the surface of the substrate
1 as in the first embodiment. The antenna elements 2 are arranged
with an equal spacing of 0.7 wavelength from a position 0.35
wavelength apart from the phase center in the zenith direction. On
the other hand, the antenna elements 3 are arranged with an equal
spacing of 0.7 wavelength from a position 0.35 wavelength apart
from the phase center in the nadir direction. The substrate 1 is
provided with flares 4 on both sides thereof in the longitudinal
direction. Incidentally, all the antenna elements 2 and 3 have the
same characteristics.
[0131] The wide-angle null-fill antenna further comprises a slot
antenna 6 extending horizontally at the phase center on the
substrate 1. The slot antenna 6 has radiation characteristics
equivalent to those of the antenna elements 2 and 3.
[0132] FIG. 22 is a diagram showing the cross-sectional view of the
substrate 1 of the wide-angle null-fill antenna of this embodiment.
As can be seen in FIG. 22, each of the antenna elements 2 and 3 is
electromagnetically coupled with a driving slot 9 formed inside the
substrate 1, and excited by the slot 9. Each of the driving slots 9
has a length of quarter-wavelength: .lamda./4 (the wavelength of
electromagnetic waves radiated therefrom).
[0133] Besides, the slot antenna 6, which is placed inside the
substrate 1 at the position of the phase center, has a length of
half-wavelength .lamda./2 (.lamda.: the wavelength of
electromagnetic waves radiated therefrom). Since the substrate 1 is
made of dielectric material, the slot antenna 6 can function as an
antenna without physically forming slots or apertures.
[0134] As is described above, according to the third embodiment of
the present invention, if only a slot having a length different
from that of the driving slots 9 is added to the phase center when
the slots 9 are formed inside the substrate 1 to excite the antenna
elements 2 and 3, the slot can function as the slot antenna 6.
Consequently, the wide-angle null-fill antenna can be manufactured
easily.
[0135] If the slot antenna 6 has the same amplitude characteristics
as those of the other antenna elements (antenna elements 2 and 3),
it is obvious that the wide-angle null-fill antenna of this
embodiment can achieve the same effect as with that of the first
embodiment. Therefore, the same description will not be
repeated.
[0136] FIG. 23 is a diagram showing a base station provided with
the wide-angle null-fill antenna depicted in FIG. 21 whose maximum
radiation direction is tilted downward (in a depression angle
direction) in the vertical plane. In FIG. 23, the wide-angle
null-fill antenna is set at the top of a building as a BTS
antenna.
[0137] In FIG. 23, the dotted line indicates the radiation pattern
of the wide-angle null-fill antenna. The beam peak indicated by the
dotted line is substantially horizontal. On the other hand, the
beam peak indicated by the solid line is oriented in a downward
direction. In this manner, when a beam is tilted downward,
interference (overreach) to adjacent areas can be reduced. Thus,
the wide-angle null-fill antenna can be effectively used as a BTS
antenna when small cells are desired.
[0138] FIG. 24 is a diagram showing the excitation phase and
excitation amplitude distributions in the wide-angle null-fill
antenna whose maximum radiation direction is tilted downward. In
FIG. 24, the solid line indicates the amplitude distribution, while
the dotted line indicates the phase distribution. The amplitude
distribution has bilateral symmetry with respect to the origin
(phase center). The phase distribution has point symmetry with
respect to the origin. More specifically, the antenna elements 2,
which are arranged from the phase center in the zenith direction,
are advanced more in phase as the distance from the phase center
increases. On the other hand, the antenna elements 3, which are
arranged from the phase center in the nadir direction, are delayed
more in phase as the distance from the phase center increases. The
excitation amplitude of an antenna element added to the phase
center is set to a value about 2 dB higher than that of adjacent
elements. This 2 dB difference is within the range of values
regarded as substantially the same.
[0139] FIG. 25 is a diagram showing the radiation pattern of the
wide-angle null-fill antenna obtained from the excitation amplitude
distribution shown in FIG. 24. As can be seen in FIG. 25, the beam
peak direction is at a depression angle of 15 degrees, and the
sidelobe level is reduced on the minus angle or elevation angle
side. As just described, in this embodiment, the excitation
amplitude of an antenna element added to the phase center is set to
be about 2 dB higher than that of adjacent elements. Thereby, the
radiation level is improved in the depression angle direction as
compared to the characteristics of the wide-angle null-fill antenna
of the first embodiment shown in FIG. 16.
Fourth Embodiment
[0140] FIG. 26 is a diagram showing the construction of a
wide-angle null-fill antenna according to the fourth embodiment of
the present invention. Referring to FIG. 26, the wide-angle
null-fill antenna comprises a substrate 1 and antenna elements 2
and 3 arrayed at regular intervals on the surface of the substrate
1 as in the first embodiment. The antenna elements 2 are arranged
with an equal spacing of 0.7 wavelength from a position 0.35
wavelength apart from the phase center in the zenith direction. On
the other hand, the antenna elements 3 are arranged with an equal
spacing of 0.7 wavelength from a position 0.35 wavelength apart
from the phase center in the nadir direction. The substrate 1 is
provided with flares 4 on both sides thereof in the longitudinal
direction. Incidentally, all the antenna elements 2 and 3 have the
same characteristics.
[0141] The wide-angle null-fill antenna further comprises a
parasitic element 7 in the vicinity of the phase center on the
substrate 1. The parasitic element 7 is spaced about 1 wavelength
apart from the phase center in the vertical direction relative to
the substrate 1. The parasitic element 7 has substantially the same
characteristics as those of the antenna elements 2 and 3. The
parasitic element 7 is excited by the antenna elements 2 or 3.
Since the parasitic element 7 is not grounded, it has wide-angle
radiation characteristics as compared to the antenna elements 2 and
3. As is described previously for the first embodiment, the phase
of electromagnetic waves radiated from the parasitic element 7 is
allowed to shift to the extent of approximately .+-.60 degrees.
Although the amount of phase shift varies according to change in
the distance between the phase center and the parasitic element 7,
such variation is of no particular concern if the phase shift is
within the allowable range (.+-.60 degrees).
[0142] Incidentally, in this example, the parasitic element 7 has
substantially the same characteristics as those of the antenna
elements 2 and 3. However, the parasitic element 7 may be a strip
metal being not grounded, the longitudinal sides of which are
parallel to the direction of polarized waves. Or, the parasitic
element 7 may be a circular metal which is not grounded.
[0143] If the parasitic element 7 has the same amplitude
characteristics as those of the other antenna elements (antenna
elements 2 and 3), it is obvious that the wide-angle null-fill
antenna of this embodiment can achieve the same effect as with that
of the first embodiment. Therefore, the same description will not
be repeated.
[0144] In the wide-angle null-fill antenna of this embodiment, the
antenna elements 2 and 3 are similar to conventional cosecant
squared beam antennas. The parasitic element 7 can be easily added
to an existing antenna afterwards. For example, by placing the
parasitic element 7 inside a radome (antenna cover), the element 7
can be easily added to an existing antenna.
[0145] FIG. 27 is a diagram showing the construction of a
wide-angle null-fill antenna in which each of rectangular patch
antenna elements in an array is provided with a rectangular
parasitic element. The size (W and H) of the parasitic element 17
is smaller than that of the patch antenna element. In this
embodiment, main parameters for forming a horizontal beam represent
the size (W and H) of the parasitic element 17. Consequently,
beamforming in the horizontal plane can be performed independently
of beamforming for mill fill in the vertical plane. With respect to
the size (W and H) of the parasitic element 17, the relation
between W and H is defined as H>W as shown in FIG. 27 in the
case of vertically polarized wave, while W and H is defined as
H<W in the case of horizontally polarized wave.
Fifth Embodiment
[0146] FIG. 28 is a diagram showing an example of the construction
of a wide-angle null-fill antenna according to the fifth embodiment
of the present invention. As can be seen in FIG. 28, the wide-angle
null-fill antenna comprises a substrate 1 and antenna arrays 2a and
3a including antenna elements arranged at regular intervals on the
surface of the substrate 1. The antenna elements included in the
antenna array 2a are arranged in a matrix with an equal spacing of
0.7.lamda.(.lamda.: the wavelength of electromagnetic waves
radiated therefrom) from positions 0.35.lamda. apart from the phase
center in the zenith direction. On the other hand, the antenna
elements included in the antenna array 3a are arranged in a matrix
with an equal spacing of 0.7.lamda. from positions 0.35.lamda.
apart from the phase center in the nadir direction. The antenna
elements are laterally spaced 0.35.lamda. or 1.05.lamda. apart from
the phase center. Incidentally, all the antenna elements of the
antenna arrays 2a and 3a have the same characteristics.
[0147] The wide-angle null-fill antenna further comprises an
antenna element 8 at the phase center on the substrate 1. The
antenna element 8 has radiation characteristics equivalent to those
of the antenna elements included in the antenna arrays 2a and
3a.
[0148] As is described previously for the first embodiment, an
antenna array consisting of antenna elements arranged in the
horizontal plane has radiation characteristics equivalent to those
of an antenna element placed in the center of the array. That is,
the wide-angle null-fill antenna of FIG. 28 has radiation
characteristics equivalent to those of the wide-angle null-fill
antenna of FIG. 7. Thus, the wide-angle null-fill antenna of this
embodiment can achieve the same effect as with the wide-angle
null-fill antenna of the first embodiment.
[0149] FIG. 29 is a diagram showing another example of the
construction of a wide-angle null-fill antenna according to the
fifth embodiment of the present invention. In FIG. 28, the antenna
arrays 2a and 3a are disposed on the substrate 1 and the antenna
element 8 is placed at the phase center. Besides, as can be seen in
FIG. 29, the wide-angle null-fill antenna may comprise, with the
same advantages, a substrate 1, slot antennas 2b and 3b arrayed on
the substrate 1, and an antenna element 8 at the phase center.
Additionally, in FIG. 28, while the antenna arrays 2a and 3a are
arranged in a matrix, they may be arranged in other forms such as a
honeycomb.
Sixth Embodiment
[0150] FIG. 30 is a diagram showing the construction of a
wide-angle null-fill antenna according to the sixth embodiment of
the present invention. FIG. 31 is a diagram showing the enlarged
side view of the vicinity of the phase center of the wide-angle
null-fill antenna. In FIGS. 21, 28 and 29, a slot antenna or a
patch antenna is employed as a center antenna element, a dipole
antenna may be used as a center antenna element. Referring to FIG.
30, the wide-angle null-fill antenna comprises a substrate 1 and
antenna elements 2 and 3 vertically arrayed at regular intervals on
the surface of the substrate 1 as in FIG. 21. The wide-angle
null-fill antenna further comprises a dipole antenna 12 at the
phase center on the substrate 1. Among the antenna elements 2 and
3, two elements at the center are spaced apart by a distance more
than the spacing between other elements to avoid physical
interference with the dipole antenna 12. The spacing between the
two center antenna elements is 1.2.lamda. (.lamda.: the wavelength
of electromagnetic waves radiated therefrom). The other antenna
elements are arranged with an equal spacing of 0.7.lamda. as in the
first embodiment. The dipole antenna 12 is placed at the center of
the 1.2.lamda. spacing: at a position 0.6.lamda. apart from each of
the adjacent antenna elements, so that it coincides with the phase
center of the antenna elements 2 and 3. Although the spacing
between the two center antenna elements may be 1.4.lamda., a
spacing of 1.2.lamda. provides better characteristics.
[0151] The dipole antenna 12 is placed on a coaxial feeder wire
with support function on the substrate 1.
[0152] In this embodiment, the amplitude characteristics differ not
more than 3 dB between the antenna elements 2 and 3 and the dipole
antenna 12.
Seventh Embodiment
[0153] FIG. 32 is a diagram showing the construction of a
wide-angle null-fill antenna according to the seventh embodiment of
the present invention. FIG. 33 is a diagram showing the enlarged
side view of the vicinity of the phase center of the wide-angle
null-fill antenna. As can be seen in FIG. 32, the wide-angle
null-fill antenna of this embodiment is basically similar in
construction and general arrangement to that of the sixth
embodiment except with a patch antenna element 13 in place of the
dipole antenna 12 at the center.
[0154] As in the sixth embodiment described in connection with FIG.
30, among the antenna elements 2 and 3, two elements at the center
are spaced apart by a distance more than the spacing between other
elements. The spacing between the two center antenna elements is
1.2.lamda.. The other antenna elements are arranged with an equal
spacing of 0.7.lamda..
[0155] A coaxial feeder wire with support function is placed on the
substrate 1 with a patch panel 14 thereon, and the patch antenna 13
is formed on the patch panel 14.
[0156] As shown in FIG. 33, the patch antenna 13 is oriented at an
angle (depression angle) with respect to the vertical direction so
that the maximum radiation direction of the antenna 13 is directed
downward with respect to the horizontal direction.
[0157] FIG. 34 is a diagram showing the construction of the
wide-angle null-fill antenna in which the patch antenna element 13
added to the phase center is tilted at an depression angle, and
also, among patch antenna elements 2 and 3, those on both sides of
the element 13 are tilted at an depression angle. With this
construction, the radiation level is further improved in a
depression angle range. The antenna elements 2 and 3 are arranged
with an equal spacing of 0.7.lamda. as in the first embodiment.
While, in FIG. 34, the patch antenna 13 and the antenna elements
adjacent thereto are tilted at the same angle, the tilt angle may
be determined according to the required radiation level.
[0158] In this embodiment, all the antenna elements 2 and 3 may be
tilted at an depression angle. Besides, an antenna array as shown
in FIG. 7 may be added to the phase center instead of the patch
antenna.
Eighth Embodiment
[0159] FIG. 35 is a diagram showing the construction of a
wide-angle null-fill antenna according to the eighth embodiment of
the present invention. FIG. 36 is a diagram showing the enlarged
side view of the vicinity of the phase center of the wide-angle
null-fill antenna. Referring to FIG. 35, the wide-angle null-fill
antenna comprises a substrate 1 and antenna elements 2 and 3
arrayed at regular intervals on the surface of the substrate 1. The
wide-angle null-fill antenna further comprises a center antenna
element (dipole antenna 15) added to the phase center of the
antenna elements 2 and 3. The antenna elements 2 and 3 are arranged
with an equal spacing of 0.7.lamda. as in the first embodiment. The
center antenna element is extended forward (in the direction in
which electromagnetic waves are radiated) to avoid overlap or
physical interference with adjacent antenna elements.
[0160] With this construction, the antenna elements 2 and 3 can be
equally spaced.
[0161] Also in this embodiment, as shown in FIG. 36, the center
antenna element (dipole antenna 15) is oriented at an angle
(depression angle) with respect to the vertical direction so that
the maximum radiation direction of the antenna is directed downward
with respect to the horizontal direction.
Ninth Embodiment
[0162] FIG. 37 is a diagram showing the construction of a
wide-angle null-fill antenna according to the ninth embodiment of
the present invention. FIG. 38 is a diagram showing the enlarged
side view of the vicinity of the phase center of the wide-angle
null-fill antenna. As can be seen in FIG. 37, the wide-angle
null-fill antenna of this embodiment is basically similar in
construction and general arrangement to that of the eighth
embodiment except that a U-shaped dipole antenna 16 is employed as
a center antenna element. The U-shaped dipole antenna 16 has a
length of half-wavelength: .lamda./2. The U-shaped dipole antenna
16 is vertically shorter than I-shaped dipole antenna, thus
avoiding physical interference with adjacent antenna elements.
[0163] The U-shaped part (head) of an antenna in practical use is
obtained, for example, by winding a wire around a ceramic cylinder
to form a spiral coil and putting a plastic cover thereon. Such an
antenna is applicable to the wide-angle null-fill antenna of this
embodiment.
[0164] In addition to the U-shaped dipole antenna, examples of the
center antenna element include a V-shaped dipole antenna, an
infinitesimal dipole element with a length of not more than
quarter-wavelength (.lamda./4), and a current element.
[0165] In this embodiment, a beam is tilted downward, and also the
excitation amplitude of the center antenna element is set higher
than that of adjacent elements. Thus, the wide-angle null-fill
antenna can effectively radiate or focus a beam to a spot at the
foot of the antenna when set on the top of a high-rise building in
an urban area.
[0166] It will be assumed that the beam peak is set at a depression
angle of 30 degrees. FIG. 39 is a diagram showing excitation
amplitude and excitation phase distributions when the beam peak is
set at a depression angle of 30 degrees. In FIG. 39, the horizontal
axis indicates positions, plus values for the nadir direction and
minus values for the zenith direction with the phase center of the
antenna elements 2 and 3 as the origin. The solid line indicates
the excitation amplitude distribution, while the dotted line
indicates the excitation phase distribution. The excitation
amplitude distribution has bilateral symmetry with respect to the
origin (i.e., the excitation amplitude distribution is symmetrical
above and below the antenna). The excitation phase distribution has
point symmetry with respect to the origin.
[0167] In the antenna elements 2 and 3, an element more distant
from the phase center is provided with the larger phase advance or
phase delay value to incline the phase distribution curve.
[0168] In this embodiment, the incline of the phase distribution
curve is set steeper as compared to the case of the first
embodiment (FIG. 16) or the third embodiment (FIG. 24) to increase
the beam tilt angle to 30 degrees. The excitation amplitude of an
antenna element added to the phase center is set to be about 6 dB
higher than that of adjacent elements.
[0169] FIG. 40 is a diagram showing the radiation pattern obtained
from the excitation amplitude distribution shown in FIG. 39. The
beam peak is at a depression angle of 30 degrees, and the sidelobe
level is suppressed in a range (a depression angle range of 0 to 30
degrees) where there is a problem of overreach to adjacent
areas.
[0170] FIG. 41 is a diagram showing radiation characteristics in a
remote area. As shown in FIG. 37, the phase in a depression angle
range of 15 to 20 degrees is opposite to that in the desired
radiation area (a depresson angle range of 30 to 90 degrees).
[0171] In order to reduce overreach to adjacent areas, it is
necessary to suppress the sidelobe in a depression angle range of
15 to 20 degrees. The sidelobe can be reduced by adjusting the
amplitude of the center antenna element, the phase of which is the
same as that in the desired radiation area.
[0172] The phase of the center antenna element is uniform in the
entire desired radiation area. Consequently, a change in the level
of the center antenna element has little effect on the radiation
pattern in the radiation area, and consideration is required only
for the sidelobe in a depression angle range of 15 to 20 degrees.
It is optimal that the center antenna element is provided with an
amplitude of about +6 dB with respect to adjacent elements.
[0173] FIG. 42 is a diagram showing the construction of a
wide-angle null-fill antenna which is provided with metal flare
plates on both sides of antenna elements to form a beam in the
horizontal plane (i.e. to narrow down the beamwidth in a sector
form). In this construction, main parameters for forming a
horizontal beam represent the angle .alpha. at which metal flares 4
are arranged and the width W of the flares 4. Consequently,
beamforming in the horizontal plane can be performed independently
of beamforming for null-fill in the vertical plane.
[0174] FIG. 43 is a diagram showing the construction of a
wide-angle null-fill antenna in which a parasitic V-shaped dipole
element is used as an antenna element added to the phase center and
excited not directly but indirectly via air by radiation waves from
an antenna array. As can be seen in FIG. 43, a parasitic V-shaped
dipole element 18 is placed about half-wavelength forwardly of the
antenna elements 2 and 3 so that the phase of radiation waves
indirectly excited is to be substantially coincident with that of
the phase center of the elements 2 and 3. The parasitic V-shaped
dipole element 18 is provided with a phase-control short-circuit
line for fine control. With this construction, the divider/combiner
circuit can be simplified, which reduces the losses.
Tenth Embodiment
[0175] FIG. 44 is a diagram showing the construction of an omni
antenna according to the tenth embodiment of the present invention.
Referring to FIG. 44, the omni antenna comprises the six wide-angle
null-fill antennas of the first embodiment arranged in a concentric
circle.
[0176] As shown in FIG. 8, the antenna array 5 of the wide-angle
null-fill antenna of the first embodiment has the phase
characteristics showing bilateral symmetry in the horizontal plane
(e.g., at angles of both plus and minus 30 degrees, the phase of
the radiation pattern is at -24 degrees). Therefore, if the
wide-angle null-fill antennas are arranged in a concentric circle,
a beam from one antenna does not interfere with beams from adjacent
antennas.
[0177] Incidentally, in the tenth embodiment, while the omni
antenna comprises the wide-angle null-fill antennas of the first
embodiment arranged in a concentric circle, the wide-angle
null-fill antennas of the second to ninth embodiments may be used
in the same manner.
Eleventh Embodiment
[0178] FIG. 45 is a diagram showing the construction of base
station equipment according to the eleventh embodiment of the
present invention. In the base station equipment, an antenna is
placed on the ground. The antenna has the same construction as that
of the wide-angle null-fill antenna of the first embodiment. The
antenna is set in a tilted position at a prescribed angle with
respect to the vertical direction so that the side which is
oriented in the nadir direction in the first embodiment is set
toward a building.
[0179] In recent years, there has been a problem that an
insensitive area or a blind zone is formed in the upper stories of
a high-rise building. The base station equipment of this embodiment
radiates electromagnetic waves toward a building from the antenna
placed on the ground. Thereby, the coverage area of the base
station equipment includes the lower to upper floors of the
building.
[0180] While, in the eleventh embodiment, the wide-angle null-fill
antenna of the first embodiment is employed, the wide-angle
null-fill antennas of the second to ninth embodiments may be used
with the same advantages.
Twelfth Embodiment
[0181] FIG. 46 is a diagram showing the construction of base
station equipment according to the twelfth embodiment of the
present invention. The base station equipment of this embodiment is
provided with the wide-angle null-fill antenna of the first
embodiment. In the base station equipment, differently from in the
conventional one, the wide-angle null-fill antenna is set with its
surface in the vertical plane so that the side which is oriented in
the nadir direction in the first embodiment is set toward a
building.
[0182] The base station equipment of this embodiment radiates
electromagnetic waves downwardly toward an adjacent building.
Thereby, the coverage area of the base station equipment includes
the lower to upper floors of the building.
[0183] While, in the twelfth embodiment, the wide-angle null-fill
antenna of the first embodiment is employed, the wide-angle
null-fill antennas of the second to ninth embodiments may be used
with the same advantages.
[0184] Incidentally, the embodiments described above are
susceptible to various modifications, changes and adaptations.
[0185] For example, in the sixth and seventh embodiments, among the
antenna elements 2 and 3, only two elements at the center are
spaced apart by a distance different than that between other
elements. However, the other antenna elements are not necessarily
spaced equally. In the sixth embodiment, for example, the dipole
antenna 12 is spaced 0.6.lamda. apart from each of the adjacent
antenna elements. The spacing between two adjacent antenna elements
may be gradually (e.g., by the same degree) increased towards the
outside, as the distance from the phase center increases, so that
the spacing between two adjacent elements most distant from the
phase center is to be 0.7.lamda..
[0186] In the sixth and ninth embodiments, the construction of the
wide-angle null-fill antenna, in which the center antenna element
is oriented at an angle (depression angle) with respect to the
vertical direction, is not shown in the drawings. However, if the
center antenna element is oriented at an angle (depression angle)
with respect to the vertical direction as in the seventh or eighth
embodiment, the direction of the maximum radiation of
electromagnetic waves can be directed downward with respect to the
horizontal direction. The same is true in the case where the
antenna elements are not equally spaced.
[0187] In the third to ninth embodiments, if the center antenna
element is provided with an electromagnetic wave absorber around it
with the supporting portion of the element as the center, it is
possible to reduce the frequency characteristics of the beamwidth
in the horizontal plane. Besides, if the electromagnetic wave
absorber is extended to adjacent antenna elements (i.e., if the
electromagnetic wave absorber is set around the center antenna
element and also extended in the horizontal direction), it is
possible to reduce the frequency characteristics of the beamwidth
in the horizontal plane as well as to increase the electric field
level on the ground.
[0188] In the above embodiments, a cosecant squared beam antenna
includes an array of 14 antenna elements, and one or more antenna
elements are added to the vicinity of the phase center of the
antenna, which are equivalent to an antenna element added to the
phase center. However, the number of antenna elements is cited
merely by way of example and without limitation. The cosecant
squared beam antenna may include more than or less than 14 antenna
elements.
[0189] Further, in the tenth embodiment, the omni antenna includes
six sector antennas with the same characteristics arranged in a
concentric circle. However, the number of sector antennas is given
only as an example and without limitation. The omni antenna may
include more than or less than six sector antennas. For example,
the omni antenna may comprise four wide-angle null-fill antennas
each having an antenna array whose array factor is flat in a range
of .+-.45 degrees. Or, the omni antenna may comprise eight
wide-angle null-fill antennas each having an antenna array whose
array factor is flat in a range of .+-.20 degrees.
[0190] Still further, the cosecant squared beam includes a modified
cosecant squared beam. Besides, the present invention is applicable
not only to base station equipment for mobile communication but
also to other radio communication equipment.
[0191] Still further, in the above embodiments, the physical center
of the antenna elements 2 and 3 is coincident with the phase
center. However, in the example of FIG. 7, if an antenna element
with a weak amplitude is added to the vicinity of the antenna
elements 2, although the phase center hardly moves, the physical
center is displaced, resulting in no coincidence between them. In
such a case, an antenna array, a slot antenna, a dipole antenna, a
U-shaped (V-shaped) dipole antenna, or the like may also be added
to the phase center. When a parasitic element is employed, the
element may be spaced a prescribed distance apart from the phase
center.
[0192] As set forth hereinabove, in accordance with the present
invention, there can be provided a wide-angle null-fill antenna
permitting little decrease in reception or input level at the foot
of the antenna, an omni antenna using the same, and radio
communication equipment.
[0193] While the present invention has been described with
reference to the particular illustrative embodiments, it is not to
be restricted by the embodiments but only by the appended claims.
It is to be appreciated that those skilled in the art can change or
modify the embodiments without departing from the scope and spirit
of the present invention.
* * * * *