U.S. patent application number 09/823392 was filed with the patent office on 2001-09-20 for radio hologram observation apparatus and method therefor.
Invention is credited to Kitayoshi, Hitoshi.
Application Number | 20010022561 09/823392 |
Document ID | / |
Family ID | 26449981 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010022561 |
Kind Code |
A1 |
Kitayoshi, Hitoshi |
September 20, 2001 |
Radio hologram observation apparatus and method therefor
Abstract
Antenna elements A1 to A24 of a ring-shaped array antenna are
selectively connected to power combiners each with a switch SH1,
SH2 and SH3 one after another. When a direct wave and a reflected
wave arrive in the directions of the antenna elements A5 and A3,
respectively, the antenna elements A2, A5 and A8 in the power
combiner SH2 are selected and their received signals are input into
a receiver Rr to obtain therefrom an output Sr(2+5+6, f), and the
respective antenna elements of the power combiners SH1 and SH3 are
sequentially selected and their received signals are input into a
receiver Rm to obtain therefrom outputs Sm(1, f), Sm(3, f). The
outputs from the receivers Rr and Rm are caused to interfere with
each other in an interferer 11 to detect an interference output to
obtain data E(K, L). The antenna elements A3, A4, A6 and A7 are
selected and their received signals are applied to the receiver Rr,
and the antenna elements of the power combiner SH2 are sequentially
selected and their received signals are applied to the receiver Rm,
by which data E(K, L) is similarly obtained. For the thus obtained
data E(K, L) an evaluation function is calculated for hologram
reconstruction.
Inventors: |
Kitayoshi, Hitoshi; (Tokyo,
JP) |
Correspondence
Address: |
GALLAGHER & LATHROP
601 CALIFORNIA ST
SUITE 1111
SAN FRANCISCO
CA
94108
US
|
Family ID: |
26449981 |
Appl. No.: |
09/823392 |
Filed: |
March 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09823392 |
Mar 30, 2001 |
|
|
|
09551099 |
Apr 18, 2000 |
|
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Current U.S.
Class: |
343/816 ;
343/725; 343/810; 343/820 |
Current CPC
Class: |
H01Q 19/067 20130101;
H01Q 9/16 20130101; H01Q 9/28 20130101; G03H 5/00 20130101; H01Q
21/205 20130101 |
Class at
Publication: |
343/816 ;
343/810; 343/820; 343/725 |
International
Class: |
H01Q 021/00; H01Q
009/16 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 19, 1999 |
JP |
110334/99 |
Jun 14, 1999 |
JP |
166485/99 |
Claims
What is claimed is:
1. A radio hologram observation apparatus comprising: an array
antenna; a fixed-reception receiver and at least one
scanning-reception receiver; antenna element selectively connecting
means for selecting at least one of antenna elements of said array
antenna and connecting said at least one antenna element to said
fixed-reception receiver, and for selecting at least one of the
other antenna elements and connecting said at least one antenna
element to said scanning-reception receiver; data acquiring means
for causing the output from said fixed-reception receiver and the
output from said scanning-reception receiver to interfere with each
other to obtain interference observation data; and control means
for obtaining said interference observation data from said data
acquiring means by sequentially switching antenna elements for
connection two said scanning-reception receiver while keeping
connection of said at least one antenna element to said
fixed-reception receiver
2. The apparatus of claim 1, wherein said control means is means
for switching said at least one antenna element connected to said
fixed-reception receiver to another antenna element and obtaining
second interference observation data while switching said at least
one antenna element for connection to said scanning-reception
receiver one after another, for calibrating said second
interference observation data and said interference observation
data on the basis of a common phase reference.
3. The apparatus of claim 1, wherein: said antenna elements of said
array antenna are divided into a plurality of groups; and said
antenna element selectively connecting means comprises a plurality
of antenna select means each of which has connected thereto said
antenna elements of one of said plurality of groups, and a
plurality of receiver select means for selectively connecting
output terminals of said each antenna select means to said
fixed-reception receiver and said scanning-reception receiver, said
each antenna select means selecting one or more of said antenna
elements of the group connected thereto and connecting them to said
output terminals.
4. The apparatus of claim 3, wherein each of said plurality of
receiver select means comprises a plurality of change-over switches
connected to the output terminals of said each antenna select
means, and a plurality of group select means having their output
terminals connected to input terminals of said fixed-reception and
scanning-reception receivers and provided with a plurality of input
terminals, and wherein each of said change-over switches is capable
of selectively connecting output terminals of said antenna select
means connected thereto to any one of said plurality of group
select means through their different input terminals, and said each
group select means is capable of selectively connecting one or more
of its input terminals to its output terminal.
5. The apparatus of claim 1, wherein said antenna element select
means comprises a plurality of receiver select means connected to
said antenna elements, respectively, and a plurality of antenna
select means having their output terminals connected to input
terminals of said fixed-reception and scanning-reception receivers
and provided with input terminals of the same number as that of
said antenna elements, and wherein each of said receiver select
means is capable of selectively connecting said antenna elements
connected thereto to the corresponding input terminals of said
plurality of antenna select means, and each of said antenna select
means is capable of connecting its one or more input terminals to
its output terminal. and each of said antenna select means is
capable of connecting one or more of its input terminals to its
output terminal.
6. The apparatus of claim 1, wherein said array antenna is formed
with antenna elements arranged in a circumferentially layered form,
said apparatus further comprising: means by which, letting the
azimuth be represented by .phi. and the position in a direction
parallel to the axis of said circumferentially layered form by Z,
an interference observation value E(.phi., Z) is Fourier
transformed for Z to obtain .GAMMA.(.phi., .PSI.) (where .PSI. is
an elevation angle); and means by which, setting
.theta.=.pi./2-.PSI., V(.phi.',
.theta.)=.intg.W(.phi.)exp(-j2.pi.sin.the-
ta.cos.phi./.lambda.).GAMMA.(.phi.+.phi.', .theta.)d.phi.is
calculated to obtain a reconstructed hologram image, where .intg.
is from -.pi./2 to .pi./2, .lambda. is the wavelength of the
received radio wave, W(.phi.) is a weighting function and .phi.' is
a noted azimuth.
7. A radio hologram observation method comprising the steps of: (1)
connecting at least one of antenna elements of an array antenna to
a fixed-reception receiver, and sequentially connecting the other
antenna elements of said array antenna to a scanning-reception
receiver; (2) causing interference between the output from said
fixed-reception receiver and the outputs from said
scanning-reception receiver one after another to obtain a first
sequence of interference observation data and storing it in storage
means; (3) connecting a different antenna elements to said
fixed-reception receiver; and (4) sequentially connecting the other
antenna elements to said scanning-reception receiver and causing
interference between the output from said fixed-reception receiver
and the outputs from said scanning-reception receiver one after
another to obtain a second sequence of interference observation
data and storing it in storage means.
8. The method of claim 7, further comprising the steps of: (5)
connecting either one of said antenna element connected to said
fixed-reception receiver in said step (1) and said antenna element
connected to said fixed-reception receiver in said step (3) to said
fixed-reception receiver and connecting the other antenna element
to said scanning-reception receiver, and causing interference
between the outputs from said fixed-reception and
scanning-reception receivers to obtain interference observation
data for calibration use; and (6) normalizing the phase of either
one of said first and second sequences of interference observation
data by said interference observation data for calibration use to
make the phase references of said first and second sequences of
interference observation data common to each other.
9. The method of claim 8, wherein the number of antenna elements
connected to said fixed-reception receiver in said sep (1) is
plural, and a relatively narrow main lobe is formed in a synthetic
antenna directional pattern of said plural antenna elements, and
wherein the number of antenna elements connected to said
fixed-reception receiver in said step (3) is plural, and a main
lobe of a synthetic antenna directional pattern of said plural
antenna elements lies in substantially the same direction as said
main lobe.
10. The method of claim 9, wherein said step (1) is preceded by a
step of detecting the direction of arrival of a stable direct wave
by means of said array antenna and at least said fixed-reception
receiver and setting said main lobe in substantially the same
direction as that of arrival of said direct wave.
11. The method of claim 10, wherein: the antenna elements of said
array antenna are divided into a plurality of groups; in said step
(1),an antenna element in the direction of arrival of said direct
wave and antenna elements on both sides of said antenna element in
the same group are selectively connected to said fixed-reception
receiver; and in said step (3), antenna elements of a group
different from that of said antenna element in the direction of
arrival of said direct wave and lying on both sides of said antenna
element in the direction of said direction of arrival of direct
wave are selectively connected to said fixed-reception
receiver.
12. The method of claim 8, wherein said array antenna is a
ring-shaped one having a radius r, and wherein, letting the number
of antenna elements of said array antenna be represented by N, the
element number by n, the wavelength of the received radio wave by
.lambda., and an equivalent radius taking into account the zenith
angle .theta. by r' (r'=r sin.theta.), and setting .phi.=2n.pi./N,
.phi.'=2n'.pi./N, .phi.' is set, then interference observation data
in each n direction of .phi.'=.+-..pi./2 is read out of said
storage means, and
V(.phi.')=.intg..sub.-.pi./2.sup..pi./2W(.phi.)exp
(-j2.pi.'cos.phi./.lambda.).multidot.E(.phi.+.phi.')d.phi.W(.phi.)=(1/.pi-
.)(1+cos(2.phi.))is calculated, and V(.phi.') is calculated while
sequentially changing .phi.' to reconstruct a hologram.
13. A dipole antenna comprising: a tubular feeding part and first
and second antenna parts formed in one piece of an insulating
material, said first and second antenna parts being extended from
one end of said feeding part in opposite directions and having a
length nearly equal to 1/4 of the effective wavelength .lambda.; a
first antenna element formed by a metal-plated layer all over said
first antenna part and extending to the edge of a through hole of
said feeding part; a second antenna element formed by a
metal-plated layer all over said second antenna part; a through
hole formed by a metal-plated layer deposited all over the interior
surface of said through hole and connected to said first antenna
element; an outer conductor formed by a metal-plated layer
deposited all over the outer peripheral surface of said feeding
part and connected to said first and second antenna elements; and a
pair of slits cut in said outer conductor between said first and
second antenna elements, said pair of slits extending a length
about .lambda./4 from one end of said feeding part.
14. The antenna of claim 13, further comprising: a reflector part
formed integrally with said feeding part and said first and second
antenna parts such that it is spaced about .lambda./4 apart from
said first and second antenna parts of said feeding part,
contiguous to or away from said pair of slits and substantially
vertical to said feeding part and that said feeding part lies at
the center of said reflector part; and a reflector layer formed by
a metal-plated layer on either side of said reflector part and
connected to said outer conductor.
15. The antenna of claim 14, wherein said reflector part has a
plurality of small holes bored therethrough around said feeding
part, and said small holes forms second through holes connected to
said reflector layer.
16. The antenna of claim 14, wherein a connector is formed at the
end portion of said feeding part on the opposite side from said
first and second antenna parts.
17. A dipole antenna manufacturing method comprising the steps of:
forming a tubular feeding part, first and second antenna parts in
one piece of an insulating material, said first and second antenna
parts extending from one end of said feeding part in opposite
directions and each having a length nearly equal to 1/4 of the
effective wavelength .lambda., and said feeding part carring at the
other end a connector part; depositing a metal-plated layer all
over the surface of said one-piece structure and the interior
surface of said feeding part; selectively removing said
metal-plated layer on the end face of said one end of said feeding
part on one side of its through hole to form an exposed part
circularly arcuate about said through hole, and removing said
metal-plated layer on the outer peripheral surface of said feeding
part lengthwise thereof between said first and second antenna parts
to form a pair of slits diametrically opposite across said through
hole and each having a length nearly equal to .lambda./4; and
removing said metal-plated layer of said connector part between
said metal-plated layer of said through hole and said metal-plated
layer of said outer peripheral surface of said feeding part.
18. The method of claim 17, wherein: during the formation of said
one-piece structure a reflector part is formed integrally with said
feeding part and said first and second antenna parts such that it
is spaced about .lambda./4 apart from said first and second antenna
parts of said feeding part, contiguous to or away from said pair of
slits and substantially vertical to said feeding part and that said
feeding part lies at the center of said reflector part; during the
formation of said one-piece structure a plurality of small through
holes are made in said reflector part around said feeding part; and
during the formation of said metal-plated layer the interior
surfaces of said small through holes are also given metal
plating.
19. The method of claim 18, wherein an S-parameter of said antenna
is measured and the lengths of said pair of slits are adjusted so
that its dip-point frequency takes a desired value.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an apparatus and method for
observing a radio hologram by a two-input interference observation
method.
[0002] The inventor of this application has proposed an apparatus
and method for observing a radio hologram in Japanese Patent
Application Laid-Open Gazette No. 11-65405 entitled "Circumference
Scanning Type Hologram Observation Apparatus and Method Therefor"
(laid open Mar. 5, 1999, corresponding German Patent Application
Laid-Open DE19838052A-1). As depicted in FIG. 1, a fixed antenna Ar
and a rotary scanning antenna Am which is driven by a motor M are
used, and the received signal from the antenna Am is received by a
receiver Rm via a rotary joint J.sub.R, whereas the received signal
from the fixed antenna Ar is received by a receiver Rr. The
receivers Rm and Ar select and amplify signals of a preset
frequency f, and output IF signals Sr(f) and Sm(.phi., f) (where
.phi. is azimuth). These output signals Sr(f) and Sm(.phi., f) are
applied to interference means 11, wherein they are caused to
interfere with each other to obtain .intg.Sr*(f). Sm(.phi., f)
(where * indicates a complex conjugate), which is detected by a
complex detector 12 to obtain measured data E(.phi.). This data is
stored in a buffer memory 21 for the rotational angle (horizontal
azimuth) of the rotary scanning antenna Am. For the stored result a
calculation/display part 22 performs a computation to reconstruct a
hologram and displays the result of computation.
[0003] By carrying out the hologram measurement as described above,
it is possible to obtain a viewing angle over the entire range of
360 degrees with no blind spots.
[0004] Because of mechanical driving of the antenna Am for rotary
scanning, the above apparatus is incapable of making fast hologram
observations. Another disadvantage is susceptibility to unstable
reflected and/or diffracted waves.
[0005] It is therefore an object of the present invention to
provide a radio hologram observation apparatus and method that
permit fast hologram observation.
[0006] Another object of the present invention is to provide a
radio hologram observation apparatus and method that permit stable
measurements unaffected by fading.
[0007] Still another object of the present invention is to provide
a dipole antenna which is simple-structured and suitable for mass
production and a manufacturing method which permits easy
fabrication of dipole antennas of uniform characteristics..
SUMMARY OF THE INVENTION
[0008] According to an aspect of the present invention, there is
provided a hologram observation apparatus which includes a cascade
connection of a plurality of antenna select means for selecting at
least one of received signals of antenna elements of a ring-shaped
array antenna and a plurality of receiver select means for
supplying the selected received signal to any one of a plurality of
receivers and in which: the received signal from the selected
antenna element is provided to a selected one of the receivers;
received signals from other selected antenna elements are provided
to another one of the receivers; and the outputs from the two
receivers are combined as a reference signal for interference with
the output from another receiver to conduct hologram
observations.
[0009] The receiver for providing the reference signal output
receives, as a synthetic directional pattern, a combined version of
received signals from a plurality of antenna elements. The antenna
elements are selected so that the main lobe of the synthetic
directional pattern is set in the direction of arrival of a radio
wave and the null in the direction of arrival of a reflected and/or
diffracted wave.
[0010] The selective supply of the antenna element received signal
to the receiver which provides the reference signal output is
fixed, and the observation is made of the interference between
received signals while sequentially switching the selective
application of antenna element received signal to the other
receiver.
[0011] According to another aspect of the present invention, there
is provided a dipole antenna which comprises: a tubular feeding
part and first and second antenna parts formed in one piece of an
insulating material, the first and second antenna parts being
extended from one end of the feeding part in opposite directions
and having a length nearly equal to 1/4 of the effective wavelength
.lambda.; a first antenna element formed by a metal-plated layer
all over the first antenna part and extending to the edge of a
through hole of the feeding part; a second antenna element formed
by a metal-plated layer all deposited all over the interior surface
of the through hole and connected to the first antenna element; an
outer conductor formed by a metal-plated layer deposited all over
the outer peripheral surface of the feeding part and connected to
the first and second antenna elements; a pair of slits cut in the
outer conductor lengthwise thereof between the first and second
antenna elements, the pair of slits extending a length about
.lambda./4 from one end of the feeding part; and a connector part
formed at the other end portion of the feeding part.
[0012] According to another aspect of the present invention, a
reflector part is formed integrally with the feeding part and the
first and second antenna parts such that it is spaced about
.lambda./4 apart from said first and second antenna parts of the
feeding part, contiguous to or away from said pair of slits and
substantially vertical to the feeding part and that the feeding
part lies at the center of the reflector part, and a reflector
layer is formed by a metal-plated layer over the entire surface
area of either side of the reflector part and connected to the
outer conductor.
[0013] According to the antenna manufacturing method of the present
invention, the above-mentioned antenna portion made of an
insulating material is molded in one piece, then the entire area of
the mold surface is given metal plating, and the plating is partly
removed to form a balun of the external conductor with first and
second antenna elements and a .lambda./4 long slit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram depicting a conventional radio
wave hologram observation apparatus;
[0015] FIG. 2A is a plan view showing an example of an array
antenna for use in the apparatus of the present invention;
[0016] FIG. 2B is a sectional view taken along the line 2B-2B in
FIG. 2A;
[0017] FIG. 3 is a block diagram depicting an example of the
functional configuration of this invention apparatus;
[0018] FIG. 4 is an equivalent circuit diagram of a Wilkinson type
power combiner with an input select switch in FIG. 3;
[0019] FIG. 5 is a block diagram depicting an example of the
functional configuration of a select control/calculation/display
part 14 in FIG. 3;
[0020] FIG. 6 is a flowchart showing the procedure of this
invention method;
[0021] FIG. 7A is a diagram showing an example of a synthetic
directional pattern by antenna elements A2, A5 and A8;
[0022] FIG. 7B is a gram showing an example of a synthetic
directional pattern by antenna elements A3, A4, A6 and A7;
[0023] FIG. 8 is a simplified showing of another example of an
array antenna;
[0024] FIG. 9 is a block diagram depicting the functional
configuration of another embodiment of the present invention;
[0025] FIG. 10 is a perspective view showing a conventional dipole
antenna;
[0026] FIG. 11A is a front view illustrating an embodiment of the
dipole antenna according to the present invention;
[0027] FIG. 11B is its right side view;
[0028] FIG. 12A is its top plan view;
[0029] FIG. 12B is a sectional view taken along the line A-A in
FIG. 11A;
[0030] FIG. 13 is a perspective view depicting a molded portion
forming a shell of the dipole antenna;
[0031] FIG. 14 is a graph showing the frequency characteristic of a
parameter S.sub.11 of the antenna; and
[0032] FIG. 15 is a diagram depicting bow-shaped first and second
antenna elements 65 and 66.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] The present invention employs an array antenna, whose
antenna elements are divided into two or more groups, and each
group is selected by antenna select means. For example, as depicted
in FIG. 2, antenna elements A1 to A24 are disposed at equiangular
intervals to form a ring in a horizontal plane. The antenna
elements A1 to A24 are half-wave dipole antennas, which are
extended vertically (normal to the plane of paper). The reference
numerals in FIG. 2 will be described later on.
[0034] Shown in FIG. 3 is an example in which the antenna elements
A1 to A24 are divided into three groups by connecting every fourth
antenna elements to one of three Wilkinson type power combiners SH1
to SH3. The Wilkinson type power combiners SH1 to SH3 are each
controlled by an input select signal to combine the power of an
arbitrary number of input signals. The Wilkinson type power
combiner with an input select switch has such a construction as
shown in FIG. 4, in which input terminals T.sub.i1, T.sub.i2, . . .
, T.sub.ip to be connected to antenna elements are selectively
connected by switches SI.sub.1, SI.sub.2, . . . SI.sub.p to
.lambda./4 transformers T.sub.m1, T.sub.m2, . . . , T.sub.mp at one
end thereof or terminating resistances R.sub.L1, R.sub.L2, . . . ,
R.sub.Lp, the .lambda./4 transformers each having a characteristic
impedance. The .lambda./4 transformers T.sub.m1, T.sub.m2, T.sub.mp
are connected at the other end to an output terminal T.sub.o and
are interconnected at the input end via resistors R.sub.1, R.sub.2,
. . . , R.sub.p. With selective control of the switches SI.sub.1,
SI.sub.2, . . . , SI.sub.p by external control signals, one or more
input terminals can be connected to the output terminal T.sub.o as
desired.
[0035] What is required here is to select one or more of a
plurality of input terminals, combine the power of input signals
applied thereto and provide the combined power to one output
terminal; hence, the above-mentioned Wilkinson type power combiners
need not always be employed. The outputs from the Wilkinson type
power combiners SH1 to SH3 are provided via switches S1 to S3 to
either one of two Wilkinson type power combiners SHr and SHm. The
outputs from the two power combiners SHr and SHm are applied to
fixed-reception receiver (hereinafter referred to also as a fixed
receiver) Rr and a scanning-reception receiver (hereinafter
referred to also as a scanning receiver) Rm, respectively.
[0036] The power combiners SH1 to SH3 constitute antenna select
means Aser for selecting antenna elements; the switches S1 to S3
constitute receiver select means for selecting either one of the
receivers Rs and Rm; and the power combiners SHr and SHm constitute
group select means for selecting the groups of antenna elements.
The antenna select means, the receiver select means and the group
select means are used to observe the interference between received
signals by the antenna elements of the respective groups.
[0037] That is, the receivers Rr and Rm select and frequency
convert received signals based on arbitrary center frequencies and
arbitrary frequency bands, and output IF signals. At the same time
the average level (amplitude) of the output IF signals is detected.
These receivers Rr and Rm can be implemented by operating, for
example, a spectrum analyzer in a zero span mode (in a frequency
sweep stop mode). The output IF signals are applied to the
interferer 11. The interferer 11 outputs as a line spectrum of a
fixed frequency the result of frequency integration of cross
spectra of the two input signals. The interferer 11 is disclosed in
detail, for instance, in Japanese Patent Application Laid-Open
Gazette No. 9-133721 entitled "Correlation Function Measuring
Method and Apparatus" (Laid open on May 20, 1997). Letting the
numbers of the antenna elements from which the received signals are
applied to the receivers Rr and Rm be represented by K and L,
respectively, and letting the receive frequency be represented by f
and the output IF signals from the receivers Rr and Rm by Sr(K, f)
and Sm(L, f), respectively, the output from the interferer 11 is
.intg.Sr*(K, f). Sm(L, f)df, where "*" represents a complex
conjugate.
[0038] The detector 12 detects the amplitude and phase of the
output line spectrum from the interferer 11. The detected complex
amplitude .nu..sub.0(K, L) normalized by a level calibrator 13 with
the detected average signal level .nu..sub.R(K) from the receiver
Rr to obtain measured data E(K, L)=.nu..sub.0(K, L)/.nu..sub.R(K).
The measured data E(K, L) is a complex number. In this way, an
interference signal between received signals by the selected
antenna elements of the two groups is produced. The thus obtained
interference signal (the measured data E(K, L) is used to calculate
an evaluation function V(.phi.') in a select
control/calculation/display part 14 and the calculated result is
displayed therein.
[0039] The select control/calculation/display part 14 effects
various kinds of control; for example, as depicted in FIG. 5, a CPU
(Central Processing Unit) 31 reads out programs from a program
memory 32 and interprets and executes instructions in the programs.
Upon setting the receive frequency and the receive frequency
bandwidth in input means 33, the CPU 31 sets the receive frequency
f and the receive bandwidth of each of the receivers Rr and Rm via
a receiver setting output part 34. The CPU 31 supplies an antenna
select signal to each of the Wilkinson type power combiners SH1 to
SH3 via an antenna select signal output part 35, enabling an
arbitrary antenna element to be connected to the switch connected
to the power combiner. The CPU 31 provides a switch control signal
via a switch control signal output part 36 to each of the switches
S1 to S3 to change over its connection. Furthermore, the CPU 31
applies a group select signal via a group select signal output part
37 to each of the Wilkinson type power combiners SHr and SHm to
selectively output an arbitrary one of signals input thereinto.
[0040] The measured data E(K, L) from the level calibrator 13 is
input via an input part 38 into the select
control/calculation/display part 14 and stored in its storage part
39. The select control/calculation/display part 14 further
comprises a phase normalization part 41 for phase standardization
of measured data, an evaluation function calculating part 42 for
calculating the evaluation function V(.phi.'), and a display 40 for
displaying the calculated evaluation function.
[0041] Next, a description will be given, with reference to FIG. 6,
of the procedure for interference observation through the use of
the apparatus described above. The procedure begins with
determining the direction of arrival of a direct wave in step 0.
This will be described later on.
[0042] Turning back to FIG. 2, a hologram observation method will
be described in connection with the case where a direct wave and an
unstable reflected wave (reflected by a moving vehicle or the like
and varying with time) are arriving from the directions of the
antenna elements A5 and A3, respectively, as viewed from the center
of array of antenna elements.
[0043] (1) The receiver select switch S1 is connected to the power
combiner SHm, that is, to the receiver Rm side, the switch S2 is
connected to the power combiner SHr, that is, to the receiver Rr
side, and the switch S3 is connected to the power combiner SHm,
that is, to the receiver Rm side. In other words, the antenna
select means for the antenna element group containing an antenna
element in the direction of arrival of the direct wave is connected
to the fixed receiver Rr and the antenna select means for the other
antenna groups is connected to the scanning receiver Rm.
[0044] (2) The power combiner SH2, which serves as antenna select
means, selectively connects the antenna elements A2, A5 and A8 to
the switch S2 but keeps all the other antenna elements disconnected
therefrom. As a result, the receiver Rr provides an output Sr'
(2+5+8, f). That is, the antenna element in the direction of
arrival of the direct wave and the antenna elements on both sides
in the same antenna element group are connected to the receiver
Rr.
[0045] (3) The power combiners SH1 and SH3, connected to the
receiver Rm side, connect the antenna elements to selected one of
the switches S1 and S2 one after another. In consequence, the
receiver Rm provides output signals Sm'(1, f), Sm'(3, f), Sm'(4,
f), . . . , Sm'(24, f) in a sequential order. These output signals
are applied to the interferer 11, wherein they are caused to
sequentially interfere with the output signal Sr'(2+5+8, f) from
the receiver Sr. The level calibrator 13 provides measured data
E(2+5+8, 1), E(2+5+8, 3), E(2+5+8, 4), . . . , E(2+5+8, 24) based
on or normalized by the output signal Sr'(2+5+8, f). These pieces
of measured data are stored in the storage part 39. That is, the
antenna elements of the other element groups are sequentially
connected to the scanning receiver Rm, and its respective outputs
are caused to interfere with the output from the receiver Rr in the
interferer 11 to obtain a first sequence of measured data, which is
stored in the storage part 39.
[0046] (4) The receiver select switch S1 is switched to the power
combiner SHr, that is, to the receiver Rr side, the switch S2 is
connected to the power combiner SHm, that is, to the receiver Rm
side and the switch S3 is connected to the power combiner SHr, that
is, to the receiver Rr side. In other words, the antenna element
select means connected to the fixed receiver Rr so far is connected
to the scanning receiver Rm, and the antenna element select means
connected to the receiver Rm so far is connected to the receiver
Rr.
[0047] (5) The power combiners SH1 and SH3, connected to the
receiver Rr side, connect the antenna elements A4 and A7 to the
switch S1 and A3 and A6 to the switch S3, and keeps all the other
antenna elements out of connection to the switches S1 and S3. As a
result, the receiver Rr yields an output signal Sr'(3+4+6+7, f).
That is, in the antenna element group connected to the antenna
element select means connected to the fixed receiver Rr, the
antenna elements on both sides of the antenna element in the
direction of arrival of the direct wave are connected to the
receiver Rr.
[0048] (6) The antenna elements of the power combiner SH2 connected
to the receiver Rm side are sequentially connected to the switch
S2, by which the receiver Rm provides output signals Sm'(2, f),
Sm'(5, f), Sm'(8, f) Sm'(23, f) one after another. These output
signals are applied to the interferer 11, wherein they interfere
with the output signal Sr'(3+4+6+7, f) from the receiver Rr. As a
result, the level calibrator 13 yields measured data E(3+4+6+7, 2),
E(3+4+6+7, 5), E(3+4+6+7, 8), . . . , E(3+4+6+7, 23) based on or
normalized by the above-said signal Sr'(3+4+6+7, f). These pieces
of measured data are stored in the storage part 39. That is, the
antenna elements of the element group belonging to the antenna
select means connected to the scanning receiver Rm are sequentially
connected to the receiver Rm, and its respective outputs are each
caused to interfere with the output from the fixed receiver Rr in
the interferer 11 to obtain a second sequence of measured, which is
stored in the storage part 39.
[0049] (7) The power combiner SH2, connected as antenna select
means to the receiver Rm, connects the antenna elements A2, A5 and
A8 to the switch S2 at the same time, providing from the receiver
Rm an output signal Sm'(2+5+8, f). This output signal is caused to
interfere with the above-mentioned output signals Sr'(3+4+6+7, f)
to obtain a reference signal Sm'(3+4+6+7, f), which is provided to
the interferer 11 for interference with the output signal
Sm'(2+5+8, f). In consequence, the level calibrator 13 provides
reference phase changing data E(3+4+6+7, 2+5+8), which is stored in
the storage part 39. That is, the antenna element in the direction
of arrival of the direct wave and the antenna elements on both
sides in the same antenna element group are simultaneously
connected to the receiver Rm, then the outputs from the receivers
Rm and Rr at that time are caused to interfere with each other in
the interferer 11, and the output from the level calibrator 13 is
stored as the reference phase changing data in the storage part
39.
[0050] (8) The outputs E(2+5+8, 1), E(2+5+8, 3), . . . , E(2+5+8,
24) provided from the level calibrator 13 in step (3) are all
normalized with the output obtained from the level calibrator 13 in
step (7); that is, the phase of the output signal Sr'(3+4+6+7, f)
is used as the reference phase. More specifically, for example, for
the output E(2+5+8, 1), the following calculation is conducted in
the phase normalization part 41.
E(1)=(E(2+5+8, 1)/E(3+4+6+7, 2+5+8)).multidot..vertline.E(3+4+6+7,
2+5+8).vertline.
[0051] For the other outputs, their phases are similarly normalized
to obtain E(3), E(4), . . . , E(24).
[0052] Since the reference phase for the outputs E(3+4+6;7, 2),
E(3+4+6+7, 5), . . . , E(3+4+6+7, 23) provided from the level
calibrator 13 in step (6) is Sr'(3+4+6+7, f), the outputs are used
intact as E(5), E(8), . . . , E(23) so that, for example,
E(2)=E(3+4+6+7, 2).
[0053] In this way, the outputs E(1) to E(24) are all normalized or
standardized by the same reference phase and are stored in this
order in the storage part 39 so that these pieces of measured data
can be read out therefrom with ease. That is, the reference phase
changing data is read out of the storage part 39, and at the same
time, the respective pieces of data of the first sequence of
measured data are sequentially read out, and then processing for
normalizing the first sequence of measured data by the reference
phase of the second sequence of measured data is performed in the
phase normalization part 41 using the reference phase changing
data. All the pieces of the measured data thus normalized by in the
same reference phase are stored in the storage part 39 in the
numerical order of the antenna elements.
[0054] (9) The pieces of measured data E(1), E(2), . . . , E(24)
are read out of the storage part 39 to perform the reconstruction
of holograms, for example, by the following calculation.
.phi.=n.pi./12, .phi.'=n'.pi./12
[0055] where: n and n'=1, 2, . . . , 24 (where 24 is the number of
antenna elements)
W(.phi.)=(1/.pi.)(1+cos(2.phi.)) (weighting function)
[0056] Letting r represent the radius of the ring-shaped array
antenna, .lambda. the wavelength of the radio wave to be observed
and r' (where r'=r sin.theta.) an equivalent radius of the array
antenna considering the zenith angle .theta. of the incoming wave,
the direction and amplitude value of the incoming wave can be
calculated by
Evaluation function
V(.phi.')=.intg..sub.-.pi./2.sup..pi./2W(.phi.)exp(-j2-
.pi.'cos.phi./.lambda.).multidot.E(.phi.+.phi.')d.phi.
[0057] That is, the calculation of the evaluation function
V(.phi.') by integrating .phi. from -.pi./2 to .pi./2 is performed
while sequentially changing the value of .phi.'. And
.phi.'=.phi..sub.max which maximizes the evaluation function
V(.phi.') is the direction of arrival of the incoming wave, and
V(.phi..sub.max) is its amplitude. For example, when .phi.'.pi.,
n'=.pi..times.(12/.pi.)=12 and (.phi.'=.pi.)-.pi./2 and
(.phi.'=.pi.)+.pi./2 are .pi./2 and 3.pi./2, respectively. Since
the values of (n+n') for them are 6 and 18, E(6) to E(18) are used
for the calculation of the evaluation function; E(6) is weighted by
a value calculated by substituting .phi.=-6.pi./12 into W(.phi.)
exp(-j2.pi.r'cos.phi./.lambda.), E(7) is weighted by a value
calculated by substituting .phi.=-5.pi./12 into W(.phi.)
exp(-j2.pi.2.pi.r'cos.phi./- .lambda.), and E(8) to E(18) are also
similarly weighted. The thus weighted E(6) to E(18) are added
together to obtain an evaluation function value V(.pi.) for
.phi.'=.pi.. That is, V(.pi.) can be obtained by the following
calculation. 1 V ( ) = n = - 6 + 6 ( 1 + cos ( n / 6 ) exp ( - j 2
r ' cos ( n / 12 ) / ) E ( n + 12 ) )
[0058] By performing such calculations while setting each
.phi.'(=.pi./12, 2.pi./12, . . . , 24.pi./12), the evaluation
function V(.phi.') is obtained.
[0059] It is also possible to precalculate
W(.phi.)exp(-j2.pi.r'cos.phi./.- lambda.) for each .phi. and
prestore it in the storage part 39 so that it may be used to
calculate the evaluation function V(.phi.') afterward. The set
angle .phi.' and its evaluation function value V(.phi.') are stored
in a storage part in the display 40.
[0060] The display 40 displays the evaluation function with the
abscissa representing .phi.' and the ordinate V(.phi.').
[0061] In the reception by the receiver Rr in steps (2) and (5),
temporal variations (i.e. phase fluctuations by multi-path
reflection) of the phase comparison reference signal Sr(K, f) is
suppressed by synthesizing the directional patterns of the antenna
elements A2, A5 and A8 and the directional patterns of the antenna
elements A3, A4, A6 and A7 such that the main lobes of the
synthetic directional patterns are set in the direction of arrival
of the direct wave and the nulls in the direction of arrival of the
reflected wave. FIG. 7A shows the synthetic directional pattern of
the antenna elements A2, A5 and A8, and FIG. 7B the synthetic
directional pattern of the antenna elements A3, A4, A6 and A7. In
either case, the direction of the main lobe BM is in the direction
of arrival of the direct wave (i.e. the direction of the antenna
element A5 as viewed from the center O of the circle of array of
the antenna elements), and the null is in the direction of arrival
of the reflected wave (the direction of the antenna element A3 as
viewed from the center O of the circle).
[0062] Steps (7) and (8) are to detect the phase difference between
phase comparison reference signals measured with the
above-mentioned two synthetic directional patterns, calculate one
of the phase comparison reference signals and obtain the measured
results of hologram observation based on the same phase
reference.
[0063] By performing steps (1) to (9) repeatedly while scanning in
the direction of the main lobe of the synthetic directional pattern
for obtaining the phase comparison reference signal, hologram
images of radio waves in plural directions of their arrival are
observed, by which it is possible to evaluate an interference
and/or disturbing wave and a multi-path reflected wave separately
of each other. That is, steps (1) to (9) are performed, for
example, after the direction of the main lobe held in the direction
of the antenna element A5 by simultaneous selection of the antenna
elements A2-A5-A8 and A3-A4-A6-A7, is switched to the direction of
the antenna element A6 by simultaneous selection of A3-A6-A9 and
A4-A5-A7-A8. Thereafter, steps (1) to (9) are similarly repeated
while switching the direction of the main lobe of the synthetic
directional pattern from one antenna element to another. A
plurality of hologram images thus obtained are observed, and radio
waves of varying relative levels are decided as interference and/or
disturbing waves and radio waves with no variations in their
relative levels are decided as a multi-path reflected waves.
[0064] Next, a description will be given of how to detect the
directions of arrival of a stable direct wave and an unstable
reflected wave in step 0 in FIG. 6.
[0065] One possible method is to find out a combination of antenna
elements receiving radio waves whose levels are close to the
maximum receiving level and temporally stable, by connecting all
the receiver select switches S1, S2 and S3 to the receiver Rr side
and arbitrarily combining the antenna elements through manipulation
of the antenna element select means Aser. That is, antenna elements
A.sub.n, A.sub.n+1 and A.sub.n+2 (where n=1) are simultaneously
connected to the receiver Rr, and the average signal level
.nu..sub.R(A.sub.n+A.sub.n+1+A.sub.n+2) from the receiver Rr at
that time is calculated. If the calculated value is not larger than
the maximum value .nu..sub.RMAX of the average signal level
obtained so far, then n is incremented by one, that is, the antenna
elements simultaneously connected to the receiver Rr are shifted
one by one, and if the calculated value is greater than the maximum
value .nu..sub.RMAX, the latter is updated with the former and n is
incremented by one. Then, the simultaneous connection of three
antenna elements to the receiver Rr, the detection of the average
received signal level, its comparison with the maximum value
.nu..sub.RMAX and the one-by-one shifting of the three
simultaneously selected antenna elements are repeated until n
reaches the maximum value (24 in the example of FIG. 2). The
direction of the antenna element A.sub.n+1 corresponding to the
value n+1 at the time the maximum value .nu..sub.RMAX is obtained
after the final processing is decided as the direction of arrival
of the direct wave.
[0066] Another method is to suitably select the antenna elements
for connection to the receiver Rr, make hologram observations and
selectively determine the direction of a stable radio wave of large
level based on the results of observations. This method involves
trials of combinations of antenna elements to be connected to the
receiver Rr and the evaluation of temporal variations in receiving
levels in plural observations that are carried out under the same
condition. In general, the measurable angular range by the
directional pattern of one antenna element is approximately
120.degree.. Hence, steps (1) to (9) are performed while changing
the direction of the main lobe of the antenna directivity for
obtaining the phase comparison reference signal through 120.degree.
at one time to make the measurement over the entire range of
360.degree., and steps (1) to (9) are performed at least three
times every 120.degree. to evaluate temporal variations of received
signals. And the direction of arrival of a stable radio wave is
determined as the direction of the direct wave.
[0067] In this way, the directions of arrival of the direct wave
and the unstable reflected wave are detected, and the antenna
elements are so selected as to obtain a synthetic directional
pattern whose main lobe is directed in the direction of arrival of
the direct wave and the null in the direction of the unstable
reflected wave. And stable hologram measurements are made possible
by performing steps (1) to (9) using the received signal of the
selectively combined antenna elements as the phase reference.
[0068] The select control/calculation/display part 14 in FIG. 3
controls the antenna selection and receiver selection for
performing steps (1) to (9), the antenna selection and receiver
selection for determining the directions of arrival of the direct
wave and the unstable reflected wave, make the correction in step
(9) for the data E(K, L) obtained, conducts the calculation in step
(9), and displays the calculated result using the set angle .phi.'
as a parameter.
[0069] The array antenna need not always be ring-shaped but it may
also be such a circumferentially layered array antenna assembly as
depicted in FIG. 8. In this case, steps (1) to (9) are performed
for the array antenna of each layer to obtain data E(.phi., Z)
(where Z represents the layer of the array antenna handled, the
data E(.phi., Z) is read out of the storage part 43 and is Fourier
transformed in the Fourier transform part 43 for Z. The
Fourier-transformed result .GAMMA.(.phi., .PSI.) (where .PSI. is
the elevation angle) is stored in the storage part 39. Then, for
each set angle .phi.' the transformed results .GAMMA.(.phi., .PSI.)
corresponding to--.pi./2 to .pi./2 are read out of the storage part
39, and the following discrete calculation is conducted setting
.theta.=.pi./2-.PSI. to obtain reconstructed hologram images.
V(.phi.',
.theta.)=.intg..sub.-.pi./2.sup..pi./2W(.phi.)exp(-j2.pi.r
sin.theta.cos.phi./.lambda.).GAMMA.(.phi.+.phi.',.theta.)d.phi.
[0070] This needs only to make the calculation for one zenith angle
.theta. for each set angle .phi.', hence permitting reduction of
computational complexity.
[0071] In the above, the antenna elements are selected prior to
selecting the receiver to which the selected antenna elements are
connected, but this order may be reversed. For example, as depicted
in FIG. 9, either one of the receivers Rr and Rm is selected for
the application thereto of the received signal from each of the
antenna elements A1 to A24 through one of receiver select switches
S1 to S24, then Rr-side and Rm side change-over contacts r and m of
the switches S1 to S24 are connected to the Wilkinson type power
combiners SHr and SHm, respectively. The power combiner SHr selects
the antenna elements in a manner to provide the reference synthetic
directional pattern, and applies their received signals to the
receiver Rr. The power combiner SHm selects the antenna elements
one after another and applies its received signal to the receiver
Rm. The process for the interference between the output from the
receiver Rr and the output from the receiver Rm in the interferer
11 and the subsequent processes are the same as described
previously with reference to FIG. 3.
[0072] The FIG. 3 embodiment has an advantage over the FIG. 9
embodiment that the number of switches used is smaller than in the
latter. In FIG. 3 the Wilkinson type power combiners SHr and SHm
may be omitted, in which case the switches S1, S2 and S3 are
connected at the contact r to the input of the receiver Rr and at
the contact m to the input of the receiver Rm. In other words, the
group select means can be dispensed with. In this instance,
however, there is a fear that a signal input into the receiver Rr,
for exampl, is reflected to the contact r of the switch S3
disconnected from the receiver Rr and then reflected by the contact
r back to the receiver Rr.
[0073] In FIG. 3, the number of antenna element groups is not
limited specifically to three. In both of FIGS. 3 and 9, the use of
three or more receivers and simultaneous processing for the
interference between the output from one reference fixed-reception
receiver and the outputs from the other scanning-reception
receivers could speed up the hologram observation.
[0074] According to the radio hologram observation apparatus and
method of the present invention, one or more of antenna elements of
the array antenna are connected to the fixed-reception receiver,
and its output is used as a reference received signal. The other
antenna elements are selectively connected to the
scanning-reception receiver one after another to provide equivalent
rotation of the antenna for the interference between the received
signal from each antenna element and the reference received signal.
The rotation of the antenna can is faster than in the case of its
mechanical driving for rotation, permitting reduction of the time
for hologram observations.
[0075] Stable measurements can be made by simultaneously selecting
two or more antenna elements to set the main lobe of their
synthetic directional pattern in direction of the direct wave.
[0076] Besides, by setting the null of the synthetic directional
pattern in the direction of arrival of the unstable reflected wave
or disturbing wave, it is possible to separate such unstable
reflected, interference and disturbing waves from the stable direct
wave, protecting the hologram observation from their influence.
[0077] Shown in FIG. 10 is an example of a dipole antenna that can
be used as each of the antenna elements A1 to A24. Reference
numeral 52 denotes a coaxial cable inserted through a hole made in
a metal reflector 51 centrally thereof with its outer and central
conductors 53 and 54 placed vertically to the reflector 51. The
heights of the outer and central conductors 53 and 54 from the
reflector surface are each set about a quarter wavelength. The
outer conductor 53 has a pair of diametrically opposed slits 55 and
56 extending down from its top to the reflector 51; namely, the
portion of the outer conductor 53 projecting upwardly of the
reflector 51 is divided into two outer conductor pieces 53a and
53b. Reference numeral 57a denotes an antenna element connected at
one end to the projecting end of the central conductor 54 and
connected to the one outer conductor pieces 53a and held in
parallel to the reflector 51. Aligned with the antenna element 57a
is an antenna element 57b connected at one end to the other outer
conductor piece 53b. The length of each of the antenna elements 57a
and 57b is approximately .lambda./4.
[0078] With this structure, the outer conductor 53 with the slits
55 and 56 equal to the .lambda./4 length constitutes a balun (i.e.,
a balanced-to-unbalanced transformer). A balance radiation element
of a dipole antenna 57 formed by the antenna elements 57a and 57b
and an unbalanced feeder line of the coaxial cable 52 are
balanced-to-unbalanced transform-connected, permitting therethrough
of the passage of an unbalanced current (a common mode current) to
the outside of the coaxial cable 52, thereby preventing unnecessary
radiation.
[0079] The antenna described above is produced by: making a hole in
the reflector 51; inserting the coaxial cable 52 with the slits 55
and 56 through the hole and soldering the outer conductor 53 and
the reflector 51; and soldering the antenna element 57a to the
central conductor 54 and the outer conductor piece 53a and the
antenna element 57b to the outer conductor piece 53b.
[0080] Because of such complex manufacturing steps involved in its
fabrication, the antenna of this example is not suitable for mass
production. Furthermore, the soldering leads to variations in
antenna characteristics, and during fabrication it is difficult to
compensate for characteristic differences resulting from variations
in properties of the materials used. To use this antenna as the
array antenna element, it needs additional working for providing
required element spacing, inevitably raising the manufacturing
costs.
[0081] A description will be given, with reference to FIGS. 11
through 13, of an example of an antenna suitable for use as the
antenna element of the apparatus depicted in FIG. 3. As shown in
FIG. 12B, a hollow, cylindrical feeding part 61 and first and
second antenna parts 62 and 63 are formed in one piece of a
synthetic resin material such as LCP (Liquid Crystal Polymer). The
first and second antenna parts 62 and 63 each have a length nearly
equal to a quarter of the wavelength X used. A reflector part 64,
which is approximately .lambda./4 away from the first and second
antenna parts 62 and 63 and is substantially parallel thereto, is
formed integrally with the feeding part 61. The feeding part 61 is
located substantially at the center of the reflector part 64. The
reflector part 64 may preferably be wide in area; for example, it
is provided in a rectangular form measuring, for example, about
.lambda.3/4 by 2.lambda., and is placed with its longer sides held
in parallel to the first and second antenna parts 62 and 63 (see
FIG. 11).
[0082] The first and second antenna parts 62 and 63 are given metal
plating to form first and second antenna elements 65 and 66. The
tubular feeding part 61 is coated over its interior surface with a
metal-plated layer to form a metal-plated through hole 68. At the
upper end face of the feeding part 61 the through hole 68 is
connected to the first antenna element 65 through a metal-plated
coupling part 69.
[0083] The feeding part 61 is coated over its exterior surface with
a metal-plated layer to form an outer conductor 71, which has a
pair of opposed slits 72 and 73 extending from the lower end face
of the feeding part 61 toward the reflector part 64. The lengths of
the slits 72 and 73 are shorter than the quarter wavelength, i.e.
.lambda./4.
[0084] The reflector part 64 is coated over its external surface
with a metal-plated reflector layer 74 and has a plurality of small
holes (eight in this example) 75 bored at equiangular intervals
about the feeding part 61. The interior surfaces of the small holes
75 are each covered with a metal-plated layer, forming a second
through hole 76 that is contiguous to the reflector layer 74.
[0085] The end portion of the feeding part 61 on the opposite side
from the first and second antenna parts 62 and 63 forms a connector
part 78, which is threaded around its outer peripheral surface and
is given metal plating. The inner diameter of the connector part
78, defined by a stepped portion 79 formed therein, is larger than
the inner diameter of the feeding part 61.
[0086] Furthermore, the illustrated antenna is configures so that a
plurality of such antennas can be combined into a ring-shaped array
antenna. To join the array antenna elements side by side, the
antenna of this example has coupling flanges 81 and 82 formed
integrally with two opposite longer marginal edges of the reflector
part 64 as depicted in FIGS. 11A and 12A. The flanges 81 and 82 are
each have a thickness about one-half of that of the reflector part
64. The flange 81 is flush with the one surface of he reflector
part 64, whereas the flange 82 is flush with the other surface of
the reflector part 64. In this example, the antenna is intended to
enable such a ring-shaped array antenna as depicted in FIG. 2 to be
formed by joining 24 antennas. The flanges 81 and 82 are formed
aslant in opposite directions at an angle .theta. nearly equal to
7.5.degree.. The flanges 81 and 82 are also given metal plating,
and they have through holes 83 for joining means.
[0087] With such a configuration as described above, a coaxial
feeder line which has a characteristic impedance of, example, 50
.OMEGA. is formed by the through hole 68 serving as a center
conductor and the outer conductor 71; the first and second antenna
elements 65 and 66 form a half-wavelength dipole antenna; the
reflector layer 74 forms a reflecting surface; and the slits 72 and
73 of the outer conductor 71, which are about .lambda./4 long, form
a balun (a balanced-to-unbalanced transformer). Thus, a dipole
antenna is obtained which suppresses an unbalanced current. Since
the through holes 76 formed by the small holes 75 are disposed
around the feeding part 61 in close relation thereto, the through
holes 76 serve as coaxial outer conductors in the reflector part
64, providing an excellent feeding part.
[0088] In the manufacture of this antenna, the feeding part 61, as
depicted in FIG. 13, a mold is used such that the first and second
antenna parts 62 and 63, the reflector part 64, the connector part
78, and the coupling flanges 81-82 are formed in one piece of a
synthetic resin material which is excellent in high-frequency
characteristic and highly heat-resistant. The synthetic resin
material used is, for example, LPC (Liquid Crystal Polymer), which
has properties such as .epsilon..sub.r=4, tan.delta.=1% or below
and heat resistance up to 250.degree.. With the view to facilitate
the molten material, the outer diameter of the feeding part 61 near
the reflector part 64 is larger than its outer diameter near the
first and second antenna elements 62 and 63, and the
cross-sectional areas of the first and second antenna elements 62
and 63 are gradually decreased with distance from the feeding part
61. In this instance, the marginal portions of the first and second
antenna elements 62 and 63 facing toward the reflector part 64 are
tapered and their marginal portions on the opposite side from the
reflector part 64 are parallel therewith. During the molding the
through hole 67 of the feeding part 61, the small holes 75 and 83
are also made at the same time.
[0089] Next, the molded structure is coated all over its surface
with a metal-plated layer. The metal-plated layer is provided by
depositing, for example, copper (Cu) to a thickness of around 10
.mu.m, then nickel (Ni) to a thickness of 5 .mu.m, and gold (Au) to
a thickness of 1 .mu.m or less. The gold coating is intended for
corrosion resistance. Such a composition of the metal-plated layer
provides a good affinity for the molding of the synthetic resin
material.
[0090] Following the metal plating, unnecessary portions of the
metal-plated layer are removed by an NC milling machine or the
like. As depicted in FIG. 11A, the metal-plated layer on the end
face of the feeding part 61 adjoining the first and second antenna
parts 62 and 63 is selectively removed at the marginal edge
diametrically opposite the first antenna part 62 across the through
hole 67 to form an exposed part 84, thereby providing the first and
second antenna elements 65 and 66. Moreover, the plated layer
deposited over the outer peripheral surface of the feeding part 61
is selectively removed to form the slits 72 and 73 which extend
from the exposed part 84 of the end face of the feeding part 61
toward the reflector part 64 and are diametrically opposite across
the through hole 67.
[0091] In this case, an S parameter S.sub.11 of this antenna is
measured by a network analyzer or the like, and the lengths of the
slits 72 and 73 are adjusted so that dip frequencies take desired
values. That is, the frequency characteristic of the parameter
S.sub.11 exhibits a dip at a resonance frequency f.sub.2 and at a
lower frequency f.sub.1 as depicted in FIG. 14. The frequency
f.sub.1 is an impedance matching point of the balun and the dipole
antenna by the slits 72 and 73, and varies with the lengths of the
slits 72 and 73. The more the frequency f.sub.1 is spaced apart
from the frequency f.sub.2, the wider the bandwidth of the antenna
becomes but the higher the voltage standing wave ratio (VSWR). As
the lengths of the slits 72 and 73 are made to approach .lambda./4,
the frequency f.sub.1 comes closer to f.sub.2. The lengths of the
slits 72 and 73 are adjusted such that the frequency f.sub.1 is,
for example, 80% of the frequency f.sub.2, though it varies with
the required value VSWR. Taking into account the specific inductive
capacity of the material for the feeding part 61, the lengths of
the slits 72 and 73 closer to .lambda.0/(4{square root}{square root
over (.epsilon..sub.r)}), the frequency f.sub.1 approaches
f.sub.2.multidot.(.lambda.0: wavelength in free space)
[0092] In FIGS. 11 and 12 there are shown sizes (in mm) of the
respective parts of a 2 GHz band antenna manufactured using LPC of
.epsilon..sub.r=4 and tan.delta.=1%. In the case of forming a
ring-shaped array antenna, the angle .theta. of each of the
coupling flanges 81 and 82 is increased or decreased, depending on
whether the number of antenna elements used is smaller or larger
than 24. In the case of a planar array antenna, the angle .theta.
is zero, that is, the flanges 81 and 82 are parallel to the
reflector part 64. The antenna can be made wide-band by making the
first and second antenna elements 61 and 62 bow-shaped as depicted
in FIG. 15. In the above, the reflector part 64 and the reflector
layer 74 may be omitted. The above-described dipole antenna and the
array antenna using such dipole antennas can be applied to other
apparatus as well as the radio hologram observation apparatus.
[0093] As described above, the dipole antenna of the present
invention is manufactured by molding the antenna-forming parts in
one piece, coating the molding with a metal-plated layer and
removing a selected area of the layer--this permits mass production
of antenna elements of close dimensional tolerances and hence of
desired characteristics. Accordingly, the dipole antenna needs no
additional working in the case of forming the array antenna. The
dipole antenna of the present invention can be manufactured at low
cost.
[0094] It is also easy to obtain desired characteristics by
adjusting the lengths of the slits 72 and 73 to compensate for
variations in the properties of the material used for the feeding
part 61.
[0095] It will be apparent that many modifications and variations
may be effected without departing from the scope of the novel
concepts of the present invention.
* * * * *