U.S. patent application number 11/369633 was filed with the patent office on 2006-09-21 for adaptive receive and omnidirectional transmit antenna array.
Invention is credited to Bing Chiang, James A. JR. Proctor.
Application Number | 20060211374 11/369633 |
Document ID | / |
Family ID | 27805265 |
Filed Date | 2006-09-21 |
United States Patent
Application |
20060211374 |
Kind Code |
A1 |
Proctor; James A. JR. ; et
al. |
September 21, 2006 |
Adaptive receive and omnidirectional transmit antenna array
Abstract
An adaptive antenna used in a receive only mode with a separate
omnidirectional transmit antenna. The arrangement is especially
effective for small, handheld wireless devices. The transmit
antenna maybe integrated with the receive array by utilizing a
horizontally polarized transmit and vertically polarized receiver
ray. In other embodiments, the transmit antenna may be physically
separate and not integrated with the receive array. In either case
there is separate receive and transmit signal port as an interface
to radio transceiver equipment. The use of an adaptive antenna in
the receive only direction has the potential to increase forward
links capacity to levels equal to or greater than reverse link
capacity. This allows for a significant increase in the overall
number of users that may be active at the same time in a wireless
system.
Inventors: |
Proctor; James A. JR.;
(Melbourne Beach, FL) ; Chiang; Bing; (Melbourne,
FL) |
Correspondence
Address: |
HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
530 VIRGINIA ROAD
P.O. BOX 9133
CONCORD
MA
01742-9133
US
|
Family ID: |
27805265 |
Appl. No.: |
11/369633 |
Filed: |
March 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11076607 |
Mar 10, 2005 |
7034759 |
|
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11369633 |
Mar 7, 2006 |
|
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|
10386393 |
Mar 10, 2003 |
6873293 |
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11076607 |
Mar 10, 2005 |
|
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60363144 |
Mar 8, 2002 |
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Current U.S.
Class: |
455/63.1 ;
455/504 |
Current CPC
Class: |
H01Q 25/002 20130101;
H01Q 1/243 20130101; H01Q 25/001 20130101; H01Q 19/32 20130101;
H01Q 3/2605 20130101; H01Q 9/42 20130101; H01Q 1/38 20130101; H01Q
3/44 20130101; H01Q 21/24 20130101; H01Q 1/245 20130101; H01Q 1/521
20130101; H01Q 9/30 20130101; H04B 7/10 20130101; H01Q 1/242
20130101 |
Class at
Publication: |
455/063.1 ;
455/504 |
International
Class: |
H04B 1/02 20060101
H04B001/02; H04B 7/00 20060101 H04B007/00; H04B 7/02 20060101
H04B007/02; H04B 1/00 20060101 H04B001/00; H04B 15/00 20060101
H04B015/00 |
Claims
1. A system for reducing the overall effect of intercell
interference and multipath fading of mobile communication device,
comprising: an adaptive directional receive antenna array coupled
to a mobile communication device for receiving transmitted signals
from a base station; and an omnidirectional transmit antenna
coupled to the mobile communication device for transmitting signals
to the base station.
2. The system of claim 1, wherein the adaptive receive array
comprises at least one parasitic element.
3. The system of claim 1, wherein the transmit antenna comprises a
radiating element disposed at a different polarization with respect
to at least one of a plurality of elements of the receive
array.
4. The system of claim 3, wherein the transmit antenna polarization
is orthogonal to receive array polarization.
5. The system of claim 1, wherein the receive array is vertically
polarized and the transmit antenna is horizontally polarized.
6. The system of claim 1, wherein the omnidirectional transmit
antenna is physically separated from the receive array.
7. The system of claim 1, wherein the mobile communication device
is used with Time-Division Duplex system, whereby the array is used
during transmit time periods be forced to operate in a directive
mode during at least some of a receive time period.
8. The system of claim 1, wherein the device uses a Code Division
Multiple Access modulation.
9. The system of claim 1, wherein an Orthogonal Frequency Division
Multiplex modulation is used.
10. The system of claim 1, wherein the omnidirectional transmit
antenna and the adaptive receive antenna array are integrated on a
single dielectric substrate.
11. The system of claim 1, wherein the omnidirectional transmit
antenna is located at a base of a housing of a hand portable device
and the receive array is located in a top portion of the
housing.
12. The system of claim 1, wherein the omnidirectional transmit
antenna and the receive array are both located in a top portion of
a housing of a handheld portable device.
13. The system of claim 1, wherein the omnidirectional transmit
antenna is bent.
14. The system of claim 1, wherein the omnidirectional transmit
antenna is attached to a rear portion of a housing.
15. The system of claim 14, wherein the omnidirectional transmit
antenna includes a hinge for extending and retracting a length of
the transmit antenna.
16. The system of claim 1, wherein the adaptive directional receive
antenna array comprises an active antenna element and at least one
passive antenna element.
17. The system of claim 16, further comprising a switch for
coupling the at least one passive antenna element to one or more
impedances in order to affect the directivity of the adaptive
directional receive antenna array.
18. The system of claim 1, wherein a portion of the adaptive
directional receive antenna array extends through a housing of a
hand portable device.
19. The system of claim 1, wherein the adaptive directional receive
antenna array and the transmit antenna being integrated into a
housing of a hand portable device.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 11/076,607, filed Mar. 10, 2005, which is a continuation of
U.S. Application Ser. No. 10/386,393 filed Mar. 10, 2003, which
claims the benefit of U.S. Provisional Application No. 60/363,144,
filed on Mar. 8, 2002. The entire teachings of the above
application(s) are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Code Division Multiple Access (CDMA) modulation and other
spread spectrum techniques now find widespread application in
wireless systems such as cellular mobile telephones, wireless local
area networks and similar systems. In these systems a connection is
provided between a central hub or base station and one or more
mobile or remote subscriber units. The base station typically
includes a specialized antenna for sending forward link radio
signals to the mobile subscriber units and for receiving reverse
link radio signals transmitted from the mobile units. Each mobile
subscriber unit also contains its own antenna, for the reception of
the forward link signals and for transmission of reverse link
signals. A typical mobile subscriber unit may for example, be a
digital cellular telephone handset or a personal digital assistant
having an incorporated cellular modem, or other wireless data
device. In CDMA systems, multiple mobile subscriber units are
typically transmitting and receiving signals on the same carrier
frequency at the same time. Unique modulation codes distinguish the
signals originating from or intended to be sent to individual
subscriber units.
[0003] Other wireless access techniques also use spread spectrum
for communications between a centralized unit and one or more
remote or mobile units. These include the local area network
standard promulgated by the Institute of the Electrical and
Electronic Engineers (IEEE) 802.11 and the industry developed
wireless Bluetooth standard.
[0004] The most common antenna used in a mobile subscriber unit is
a monopole. A monopole antenna most often consists of a single wire
or other elongated metallic element. A signal transmitted from such
a monopole antenna is generally omnidirectional in nature. That is,
the signal is sent with approximately the same signal power in all
directions in a generally horizontal plane. Reception of a signal
with a monopole antenna element is likewise omnidirectional. A
monopole antenna therefore cannot differentiate between signals
originating from one direction versus a different signal
originating from another direction. Although most monopole antennas
do not produce significant radiation in the elevation plane, the
expected antenna pattern in three dimensions is typically a
donut-like toroidal shape, with the antenna element located at the
center of the donut hole.
[0005] Unfortunately, CDMA communication systems are typically
interference limited. That is, as more and more subscriber units
become active within a particular area and share access to the same
base station, interference increases among them, and thus so does
the bit error rate they experience. To maintain system integrity in
the face of increasing error rates, often the maximum data rate
available to one or more users must be decreased, or the number of
active units must be limited in order to clear the radio
spectrum.
[0006] It is possible to eliminate excessive interference by using
directive antenna at either the base station and/or the mobile
units. Typically, a directive antenna beam pattern is achieved
through the use of a phased array antenna at the base station. The
phased array is electronically scanned or steered desired direction
by controlling the phase angle of a signal input to each antenna
element.
[0007] However, phased array antennas suffer decreased efficiency
and gain as elements become electrically small as compared to the
wavelength of the radiated signals. When phased arrays are used or
attempted to be used in conjunction with a hand-held portable
subscriber unit, the antenna array spacing must be relatively small
and therefore antenna performance is correspondingly
compromised.
SUMMARY OF THE INVENTION
[0008] Several considerations should be taken into account when
designing an antenna for a hand-held wireless device. For example,
careful consideration should be given to the electrical
characteristics of the antenna so that propagating signals satisfy
predetermined standards requirements such as, for example, bit
error rate, signal to noise ratio or signal to noise plus
interference ratio.
[0009] The antenna should also exhibit certain mechanical
characteristics to satisfy the needs of a typical user. For
example, the physical length of each element of the antenna array
depends upon the transmit and receive signal frequency. If the
antenna is configured as monopole, the length is typically a
quarter length of a signal frequency; for operation at 800
MegaHertz (MHZ) (one of the more popular wireless frequency bands)
a quarter wavelength monopole must typically be in the range
3.7''long.
[0010] The antenna should furthermore present an esthetically
pleasing appearance. Especially when used in a mobile or handheld
portable unit, the whole device must remain relatively small and
light with a shape that allows it to be easily carried. The antenna
therefore must be mechanically simple and reliable.
[0011] In CDMA systems in particular, another consideration
involves controlling the capacity of the overall network. Some have
provided for adaptive antenna arrays for use on a reverse link of a
CDMA system in a handset. These directional antenna arrays can be
used to increase system performance by decreasing interference from
surrounding base-stations and/or other handsets. However, employing
directional antennas on the reverse link complicates the
performance of power control systems. That is, as in most wireless
communication systems, the power level of signals radiated from
handsets must be carefully controlled in order to avoid
interference to other handsets so that the signal powers arrive at
the base or other central site within a known power level
range.
[0012] The present invention comes about from realizing the
advantages of a mobile-subscriber device that uses a directional or
other adaptive antenna array together with a separate transmit
antenna. The directional adaptive antenna array, which is used only
to receive signals, may typically consist of a number, N, of
monopole antenna elements. These monopole elements can be formed as
conductive segments on a portion of a dielectric substrate such as
a printed circuit board. To complete the array, at least one
element is designated as an active antenna element which is also
disposed on the same substrate as one or more passive elements. In
a preferred embodiment, the active element is disposed in the
center of the array and the number of passive elements is two.
[0013] The separate transmit antenna may be integrated with the
receive array. In a preferred embodiment, the transmit antenna is
an omnidirectional element.
[0014] In other embodiments, the transmit antenna may be physically
separated such as on the opposite side of the housing. That is, the
receiver array may be positioned on the top of the handset with the
transmit antenna on the lower portion thereof. In either case there
is a separate receive and transmit interface port to the two
antennas.
[0015] By utilizing a horizontally polarized transmit and
vertically polarized receive array, isolation between the two
antennae is improved.
[0016] CDMA based systems that exist today, such as IS-95 and
IS-2000, have a capacity limitation problem. The limitations
largely occur on the forward link, and result from some channel
interference. This interference originates from both adjacent cells
as well as from users within the same cell. Indeed, the difference
in capacity between the forward and reverse links can be estimated
to be as high as 50 to 100%. For voice and circuit switched data
systems, the number of users that can be simultaneously supported
is defined by the less capacious of the two links. Therefore, the
limitation on the forward link actually limits the total number of
users, and the excess capacity of the reverse link is wasted.
[0017] The use of an adaptive antenna in the subscriber unit on the
receive side has the potential to increase the forward capacity to
levels equal to or greater than the reverse capacity. This allows
for a significant increase in the overall number of users without
directly increasing the reverse capacity.
[0018] It is also envisioned that other types of systems, such as
Time Division Duplex (TDD) systems, may also advantageously use the
adaptive array for receive but to steer in an omnidirectional mode
during transmit periods. The effect is achieves a similar result.
It is also expected that when TDD systems are in a stationary or
slow moving environment, a directional transmit may also be able to
be utilized.
[0019] In accordance with its key aspects, the present invention
consists of an antenna system in which an adaptive array is used
for receiving signals and an omnidirectional antenna is used for
transmitting. In preferred embodiments, the adaptive antenna is
integrated into the housing of a handheld wireless communication
unit, such as a mobile telephone unit, personal digital assistant
or the like.
[0020] The adaptive array used for receive mode is preferably an
array that uses parasitic, passive elements to achieve
directionality.
[0021] In further aspects, the omnidirectional transmit antenna is
physically and/or electrically separated from the receiver array.
The omnidirectional transmit antenna may be integrated at a
different polarity. For example, a vertically polarized receive
array may have a horizontally polarized transmit element. In other
instances, the separation can be provided by a physical distance
such as by integrating the transmit antenna and the base of a
handheld telephone unit.
[0022] The exact type of Radio Frequency (RF) modulation associated
with the invention may be of many different types. For example, the
invention can be utilized in Code Division Multiple Access (CDMA)
systems as well as other Orthogonal Frequency Division Multiplexing
(OFDM) or spread spectrum systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments of. the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0024] FIG. 1 is a high level schematic diagram of a wireless
communication device incorporating an adaptive antenna array.
[0025] FIGS. 2A-2C show various arrangements in which a
horizontally polarized, or predominantly horizontally polarized,
omnidirectional transmit antenna is incorporated within the same
device.
[0026] FIGS. 3A-3C illustrate an alternate embodiment for the
transmit antenna, mounted on the backside of a handset.
[0027] FIG. 4 is a more detailed plan of a three element receive
array.
[0028] FIG. 5 is a circuit diagram showing one possible feed
structure for the array.
[0029] FIG. 6 is a schematic diagram illustrating how the array can
be integrated into a handset.
[0030] FIGS. 7A-7C illustrate a three-dimensional radiation
pattern, azimuthal pattern and elevational pattern for the adaptive
array.
[0031] FIGS. 8A-8C illustrate the gain patterns of a horizontal
monopole transmit element in the three-dimensional, azimuthal and
elevational planes.
[0032] FIGS. 9A-9C illustrate gain patterns of the bent horizontal
monopole element operating in a PCS radio frequency band.
[0033] FIGS. 10A-10C illustrate three-dimensional, azimuthal, and
elevational patterns for a bent monopole transmit element and its
affect on the receive array.
DETAILED DESCRIPTION OF THE INVENTION
[0034] A description of preferred embodiments of the invention
follows.
[0035] Turning attention now to the drawings, FIG. 1 illustrates a
wireless device 100 that consists of a housing 110 having
incorporated therein an antenna array 120. In general the device
100 is some form of wireless communications device, such as a
cellular mobile handset, or a personal digital assistant such as a
Palm Pilot.
[0036] The antenna array 100 provides for directional reception of
forward link radio signals. The forward link signals may be
transmitted from a base station, in the case of a cellular handset
100, or from a access point, in the case of a wireless data unit
100 making use of wireless local area network (WLAN) protocols. By
directively receiving signals originating more or less from the
location of a particular base station and/or access point, the
antenna array 120 assists in reducing the overall effect of
intercell interference and multipath fading for the mobile unit
100. Moreover, as will be understood shortly, since antenna beam
patterns generated by the antenna array extend outward in a desired
direction, but are attenuated in most other directions, less power
is required for effective transmission by the base station.
[0037] In an example embodiment, the antenna array 120 consists of
a center element 102 and a pair of passive elements 104, one on
each side thereof. As will be understood shortly, the passive
elements 104 can each be operated in either a reflective or
directive mode; it is through this expediency that the array 120
can be steered to a particular direction. Although this embodiment
shows three elements, it should be understood that the array 120 is
not so limited, and that one, four, or even more passive elements
may be included. Yet other embodiments are possible for the antenna
array such as phased array, where the center element 102 is absent
and the other elements are themselves used as active elements,
together with active signal combining circuitry. We believe that a
simple N passive element array is preferred, however, because of
its low cost and high radiation efficiency.
[0038] FIGS. 2A-2C illustrate various possible placements for a
separate transmit antenna 200 in accordance with the present
invention. In the embodiment shown in FIG. 2A, the transmit antenna
200 is placed on the same circuit board as the antenna array 120.
In this particular embodiment, the transmit antenna 200 has a
horizontal orientation as opposed to the vertically oriented
elements of the receiver array 120. This orthogonal arrangement
provides for greater isolation between the two antenna sets.
[0039] In an alternate embodiment shown in FIG. 2B, the transmit
antenna 200 can be placed at the lower end of the handset 110
housing. This provides for even more electromagnetic isolation due
to the physical distance between the horizontal element 200 and the
elements of the receive array 120. This also tends to move a high
power microwave region associated with the transmit antenna 200
closer to a region of the user's chin, rather than the user's
brain.
[0040] In still other embodiments, as shown in FIG. 2C, an end
portion of the transmit antenna 200 may be bent. The bent portion,
which itself may then become more or less parallel with the
elements of the directional array, allows for more design freedom.
For example, this type of antenna can be used at a lower frequency
where the overall length of the antenna must be longer but must
still fit within the width of the handset. The bent element 200
might also be used to accommodate other components within the
handset 110 such as a keypad. The bent arrangement also avoids
radiation in the horizontal plane when the handset is held near a
vertical position. This can provide for improved performance in all
orientations of the handset 110.
[0041] FIGS. 3A-3C show still further possible embodiments of the
transmit element 200, with FIG. 3A being a side view and FIG. 3B
being a rear view of the housing 110. Here the transmit antenna 200
is a relatively short length for operation at relatively high
frequencies such as in Personal Communication Services (PCS) type
frequencies that typically are in the range of 1900 MegaHertz
(MHZ). However the element 200 can be provided with a hinge 210
allowing for an elongated section 220 to provide dual mode
operation. The overall length of the fully deployed antenna element
can be made to resonate at a lower frequency, such as the 800 (MHZ)
frequency associated with standard cellular telephone
communication. The hinged or flipping arrangement for the element
200 assures that it can either resonate within one band or the
other. It is therefore preferred to sliding or telescoping
arrangements which might lead to the user not fully deploying the
element 200 at the proper length.
[0042] In this embodiment a feedpoint 230 associated with the
transmit antenna 200 may actually be placed in an offset position
that is not completely at one end of the element 200. This offset
feedpoint location 230 allows the resonant length ratio to fit the
1900/800 MHZ frequency ratio.
[0043] FIG. 4 is more detailed view of the adaptive directional
array 110. Here the array 110 is disposed on portions of a
dielectric substrate such as a printed circuit board, including the
center element 102 and passive elements 104A and 104C previously
described. Each of the passive elements 104 can be operated in a
reflective or directive mode as will be understood shortly.
[0044] The center element 102 comprises a conductive radiator 106
disposed on the dielectric substrate 108. The passive elements 104A
and 104C themselves each have an upper conductive segment 110A and
11A as well as a corresponding lower conductive segment 112A and
112C. These segments 110A, 110C, 112A, and 112C are also disposed
on the dielectric substrate 108. The lower conductive segments 112A
and 112C are in general grounded. Also, in general, the upper
segments 110A and 110C and the lower 112A and 112C are of equal
length.
[0045] When the upper conductive segment of one of the passive
elements 104, for example the upper conductive segment 110A, is
connected to the respective lower conductive segment 112A, the
passive element 104A operates in a reflective mode. This results in
received Radio Frequency (RF) energy being reflected back from the
passive element 104A towards its source.
[0046] When the upper conductive segment 110A is open (i.e., not
connected to the lower conductive segment 112A or other ground
potential) the passive element 104A operates in a directive mode,
in which the passive element 104A essentially is invisible to the
propagating RF energy which passes therethrough.
[0047] In one embodiment, the center element 102 and the passive
elements 104A and 104D are fabricated from a single dielectric
substrate such a printed circuit board with the respective elements
disposed thereon. The passive elements 104A and 104C can also be
disposed on a deformable or flexible substrate or attached to one
surface of the center element 102 as well.
[0048] A microelectronics module 122, including respective switch
modules 116A and 116C, may also be disposed on the same substrate
108 with conductive traces 124 being provided therebetween. The
signals carried on the conductive traces 124 control the state of
the components within the microelectronic modules 116A and 116C
that achieve particular operating states for the passive elements
104A and 104C, e.g., to place them in either the reflective or
directive state as described above. Further connected to the
microelectronics module 122 is an interface 125 for providing
electrical signal control connectivity between the array 120 and an
external controller device such as located in the remainder of the
handset 100. Interface 125 can be constructed from either a rigid
or flexible material such as ribbon cable or other connector, for
example.
[0049] FIG. 5 illustrates one possible feed structure for the array
120 in more detail. A switch control and driver 142 associated with
the electronics module 122 provides logic control signals to each
of the respective control modules 116A and 116C associated with the
respective elements 104A and 104C. For example, each such control
module 116 may have associated with it a switch S1 or S2 and two
impedances Z1 and Z2. The state of the switches S1 or S2 provides
for connection states of either connecting the first impedance Z1
or the second impedance Z2. In a preferred embodiment, the second
impedance Z2 may be 0 ohms and the first impedance Z1 may be
infinite, thus providing the desired short circuit to ground or
open circuit. However, it should be understood that other values of
the impedances Z1 and Z2 are possible, such as various reactive
values.
[0050] Here it is also evident that the center element 102 is being
directly driven to the receiver circuitry 300 associated with the
handset. Thus, unlike other types of directive arrays, this
particular directive array 120 has an advantage in that it is quite
simple in operation, and complex combiners and the like are not
necessary.
[0051] FIG. 6 is a exploded view of one possible implementation
showing the directive array 120 formed on a printed circuit board
and placed within a rear cover of a handset, for example. A center
module 410 may include electronic circuitry, radio reception and
transmission equipment, and the like. A final module 420 may serve
as, for example, a front cover of the device. What is important to
see here is that the printed circuit board implementation of the
100 can be easily fit within a handset form factor.
[0052] FIG. 7A and 7B are antenna patterns illustrating performance
of the array 120 as housed in a handset. The gain achievable is
about 3 dBi. FIG. 7A is a three dimensional radiation pattern (in
the X, Y and Z directions with respect to the referenced diagram
shown for the handset 500).
[0053] FIG. 7B illustrates the azimuthal radiation pattern
achievable when one of the elements is placed in directive mode and
the other element is placed in reflective mode. The conducting
element (which is made electrically longer in the Z direction),
intercepts the received radio wave and reflects it. This creates a
null in the negative X direction. Since there is no electromagnetic
blockage in the +X direction, the wave passes through and creates a
peak. The dimension of the circuit board in the X direction is not
similar to the resonant wavelength, so that the signal is able to
circulate all the way around the azimuthal plane.
[0054] The pattern in FIG. 7C, an elevational pattern, should be
compared to an ideal symmetrical pattern to illustrate the effect
of the housing 110. The comparison shows that the overall effect on
the azimuthal plane is a slight skewing of the beam, about
15.degree. away from the X-axis. The pattern of FIG. 7C also
illustrates "necking-down", which is an effect of placing the
radiating element in a handset. Good directivity is seen, at least
along an approximate 180.degree. azimuthal plane, although skewing
is evident.
[0055] FIGS. 8A-8C are similar to FIGS. 7A-7C, although illustrate
patterns the horizontal transmit antenna element 200. This
particular embodiment, with the reference physical drawing 510
shown in the upper left hand corner, was for a bent horizontal
monopole element. The gain pattern in three-dimensions is
relatively uniform, as shown in FIG. 8C. The radiation pattern
approaches a symmetric toroid with a gain of approximately 2.1 dBi.
Again, the radiation pattern is offset somewhat through the effects
of the handset enclosure 110. However, relatively omnidirectional
performances, other than in the azimuthal plane (as shown in FIG.
8B) is the overall desired effect.
[0056] FIGS. 9A-9C are simulated gain patterns of a bent horizontal
monopole designed for the 800 MHZ cellular band, but operating in
the higher frequency PCS band. The radiation pattern, as is evident
from the view of FIG. 9A, is a cut toroid standing its "uncut"
side. The gain is 4.2 dBi. The antenna is evidently radiating at
its higher order mode, but is radiating effectively and thus can be
used as a PCS radiator at 1900 MHZ. As evident from FIGS. 9B and
9C, as at least some useable radiation pattern is seen in the
azimuthal direction.
[0057] Finally, FIGS. 10A-10C illustrate the effect of adding a
bent monopole together with the array 120 through a simulation
process. In this simulation, a horizontal bent monopole 200 and the
extending ground strip were added to the antenna array 120; only
slight distortions were found. The beam is tilted upward by
15.degree. (as shown in the elevational plot of FIG. 10C). The gain
provided is 4.7 dBi with a beamwidth of 145.degree. in the
azimuthal plane. This illustrates that the bent monopole does not
appreciably affect the operation of the array in the directional
modes.
[0058] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *