Note: Descriptions are shown in the official language in which they were submitted.
~ACKGROUND OF TE113 INVENTION
The present invention relates to a mlcrostrlp ant~nna
of two-frequency separate~feeding type for circularly
polarized waves which is employed for various radio
communications.
A microstrip antenna ls of wide applicatlon as an
antenna for varlous communica-tions, because lt has a planar
structure of a thickness sufficlently small as compared wlth
the wavelength used and ls lightweight. With a phased array
antenna using a plurality o~ such microstrip antennas it is
possible to electrically change a beam of radio wave by
controlling the phase shift amount of a phase shifter con-
nected to each antenna element. Such a phased array antenna
features its thin, small and lightwelght structure, and
hence is expected to be applied to mobile communication and
the like.
As is well-known in the art, the micro~trip antenna is
narrow-band. For example, assuming that a voltage standing
wave ratio o~ the antenna, i.e. a crikerlon upon which to
determine whether or not the antenna can be put to praatlcal
use, is 2 or below, the bandwidth of the microstrip antenna
whlch satisfles the ratlo is a9 ~mall as several percents
with respect to the center frequency, though it depends on
the characterlstic of a dielectric plate used. This means
that an ordinary microstrip antenna cannot be used for
communications ln which transmit and receive radio wa~Ps
higher than such a bandwidth as mentioned above, To solve
this problem, mlcrostrip antennas o~ various struotures have
been proposed so far.
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However, conventional art has defects such as compli-
cated structure and difficulty in fabrica~ion.
SUL~MARY OF THE INVENTION
Therefore, an object of the present invention is to
provide a microstrip ante~na of two-fre~uency separate~
feeding type for circularly polarized waves which is small in
size and easy to manufacture.
With a view to solviny the above-noted problems, the
microstrip antenna of the present invention features a
structure in which four radiation conductors are disposed on
a dielectric plate mounted on a conducting ground plane and
each radiation conductor has its marginal portion partly
short-circuited via a short-circuiting conductor to the
conducting ground plane and is supplied at its ~eeding point
with power via a feeder passing through the conducting
ground plane and the dielectric plate, and in which the four
radiation conductors are composed o~ two pairs of radiation
conductors of different sizes adjusted so that two desired
frequencies can simul-taneously be used for transmission and
for reception, respectively, the conductors of each pair
being arranged to generate a circularly polarized wave.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described in detail below
in comparison with prior art with reference to accompanying
drawings, in which:
Figs. lA and lB are a plan view and a sec-tional view
taken on the line A-A' therein, both illustrating an embodi-
ment of the present invention;
Figs. 2, 3A and 3B are plan views illustrating other
embodiments of the present invention;
Fig. 4A is a block diagram showiny transmitting-
receiviny equipment ln which a transmitting device and a
receiving device are connected to the microstrip antenna of
two-frequency separate-feeding type for circularly polarized
waves according to the present, shown in Fig. 1, 2, 3A, or
3B;
Fig. 4B ls a block diagram illustrating a phased array
antenna which is formed, as antenna elements, by the use of
the microstrip antenna of two-frequency separate-feeding
type for circularly polarized waves of the present invention
shown in Fig. 1, 2, 3A or 3B;
Figs. 5A and 5B are a plan view and a sectional view
taken on the line B-B' illustrating a conventional micro-
s-trip antenna for circularly polarized waves designed for
wide-band use;
Figs. 6A and 6B are a plan view and a seckional view
taken on the line C-C' for illustrating a conventional
microstrip antenna oE two-fre~uency separate feeding type
for circularly polarized ~aves;
Figs. 7A and 7B are a plan view and a sectional view
taken on the line D-D', showing a conventional one-point
feeding type microstrip antenna for circularly polarized
waves; and
Fig. 8 is a block diagram showing a phased array
antenna employing the conventional wide-band micros-trip
antenna for circularly polarized waves depicted in Fig. 3.
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D~TA~I.ED DESCRIPTIOM
To make cliEferences between prior art ancl the present
invention clear, examples of prior art will first be
described.
S Figs. 5A and 5B show in combina-tion an examples of the
structure of a conventional microstrip an-tenna intended for
enhanced bandwiclth, Fig. SA being a plan view and Fig. 5B a
sectional view taken on the line B-B' in Fig. 5A. Reference
numeral 51 indicakes a radiation conductor, 52 a passive
radiation conductor, 53 and 53' feeding points, 54 a
grounded conductor, 55 dielectric substrate, and 56 a
feeder. The feeding point 53 is connected to the feeder 56
feeding via a connector provided on the grounded conductor
54. With the structure of this example, an antenna which
resonates in the transmi-tting or receiving fre~uency band
can be obtained by adjustment of the sizes of the radiation
conductor 51 and the passive radiation conductor 52.
Fig. 8 is block diagram showing a conventional phasecl
array antenna using microstrip an-tennas exemplified in E'ig.
5. Reference numeral 81 indicates each an-tenna element, 82
a directional coupler for generating a circularly polarized
wave, 83 a phase shifter, 84 a power divider, 85 a diple~er,
86 a transmitter, 87 a receiver, and 88 a dummy load. By
changing the phase of a feed signal by the phase shifter
83 for each antenna element 81, the direction of the beam
can be controlled electrically.
Figs. 6A and 6B show in combination another example of
the conventional antenna structure which is simultaneously
operable for transmission and for reception, Fig. 6A being
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its plan view and Fig. 6B its sectional view takell on the
line C-C' in Fig. 6A. Reference numeral 61 indicates an
annular microstrip antenna ta radiation concluctor for
reception), and 62 a circular mlcrostrip antenna (a radi~
S ation conductor for transmission). These antennas are fed
from their back sides independently of each other through a
transmitting feeder 66 and a receiving Eeeder 68 to a
transmitting feeding point 63 and a receiving feeding point
63, respectively. With this structure, the annular micro-
strip antenna 61 and the microstrip antenna 62 resonate inreeeive and transmit frequeney bands, respectively. In this
example, reference numeral 64 is a conducting ground plane,
and 65 a dielectrie substra-te.
The antenna for cireularly polarized waves usually
employed in mobile communication can be implemented by
feeding at two points as mentioned above in connection with
Figs. 5A, 5B and 6A, 6B, and there has also been well known
a circular polarized antenna of one-poin-t feeding whlch has
only one feeding point as shown in Figs. 7A and 7B. In
Figs. 7A and 7B the function of an antenna for circularly
polarized waves which has only one feeding point 73 is
obtainable by the additional provision of protrusions 72 on
a radiation conductor 71. In this example, reference
numeral 74 is a conducting ground plane, 75 a dielectric
plate, and 76 a feeder.
In case of constructing a phased array antenna through
use of the above-descrihed prior art, the wide-band micro-
strip antenna or dual-frequency resonance type microstrip
antenna shown in Fiys. 5A and 5B poses a prob1em as the~ are
complex in clesign and construction.
In addition, since the feeding portion is co~mon to
transmission and reception and the phased of transmission
and recepti~n are controlled by -the same phase shifter 83
as shown in Fig. 8, the prior art possesses a shortcoming
that -transmission and received beams do not correspond to
each other owing to a difference in frequency therebetween,
and the diplexer 85 which mus-t be provided between the phase
shifters 83 and the transmi-tter 86 and the receiver 87 for
separating transmission and received signals makes the
feeding portion bulky. Reference numeral 81 indicates
antenna elements, 82 directional couplers, 84 a power
combiner/divider, 85 a diplexer, and 8~ a dummy load.
The antenna structure having an annular microstrip
antenna and a circular microstrip an-tenna disposed thereon,
shown in Figs. 6A and 6B, does not call for a diplexer or
circulator, because a feeding point for transmission 63 and
a receiving feeding point 67 are sufficiently isolated from
each other electrically. Howeverl this antenna struc-ture is
two-layer and hence is more complex in cons-truc-tion and
heavier than an antenna of a one-layer s-tructure, and the
manufacture of this antenna involves many steps and requires
high machining accuracy.
The circular polarized antenna of one-point feeding
depicted in Figs. 7A and 7B is not suitable as an antenna
for wide-band communications, because it is narrow-band
rather than the usual microstrip antenna and has Erequency
dependence of its axial ratio.
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The present invention i5 intended to solve the above-
mentioned problems of the prior art and thereEore -to provide
a microstrip antenna of two-Ereq~lellcy separate feediny type
which is small in size and easy to m~nufacture.
The present invention will now be described.
~Embodiment 1)
Figs. lA and lB illustrate in combination a first
embodiment of the present invention as being applied to a
microstrip antenna in which one side of each radiation
conductor is short~circuited. Fig. lA is a plan view of the
antenna and Fig. lB a sectional view taken on the line A-A'
in Fig. lA. As shown, four radia-tion conductors 111 through
114 are disposed on a dielectric plate 15 and are short-
circuited to a conducting ground plane 14 via shor-t-
circuiting conductors 121 through 124, respectively. Refer-
ence numerals 131 to 134 denote feeding points of the
radiation conductors 111 to 114, respectively, which are fed
with power ~rom its back side through feeclers ~a feeder 161
at a feeding point 131). The radiation conductors 111 and
112 are of the same size and have the sarne resonance fre-
quency tuned to a frequency of a transmitting wave, whereas
the radiation conductors 113 and 114 are of the same size
and have -the same resonance frequency tuned -to a frequency
of a receiving wave. Consequently, the radiation conductors
111 and 113 are different in size.
As regards transmission, signals fed in phase to the
radiation conductors 111 and 112 are thereby rendered into a
circularly polarized wave, which must be formed within the
half wavelength of the frequency used, as is well-known in
the art. The same is true o:E reception, because of reversi~
bility of the antenna and the .rece:iviny antenna is Eormed by
the radiation conductors 113 and 114 for receivin~ the
circularly polarized wave. The radiation conductors 111,
112 for transmission and the radiation conductors 113, 114
for reception are disposed in such a manner as not to
in-terfere with each other. To mee-t wi-th these requirements,
the radiation conductors 111, 11.2, 113 and 114 are disposed
as shown in Fig. 1, and for each radiati.on conduc-tor, a
plane passing through its feeding point and perpendicular to
the corresponding short-circuiting conductor (a plane A-A'
for the conductor 111, for instance) forms a rectangle or
square on the dielectric plate 15.
By limiting the sizes of the radiation conductors 111
through 114 to the bandwidths necessary for transmission and
recep-tion it is possible to prevent the coupling between
transmission and reception from constituting an obs-tacle to
communications. The feeding points 131 and 132 are each
connected from the back side of the conducting ground plane
14 to a transmitter via a feeder and a directiorlal coupler.
Since the radiation conductors 111 and 112 generate linearly
po]arized waves perpendicularly intersecting each other, a
transmitting circularly polarized wave can be generated by
feeding from a direc-tional coupler 421 through feeder 463
and 464 to feeding points as shown in Fig. 4A so that the
phases of feeding are displaced 90~ apar-t from each other.
Whether the polarized wave is right-handed or left~handed is
determined by the direction of connection oE the directional
coupler. For reception as well, a circularly polarized wave
is rece.ived via radiation concluctors 411 and 412, .eeeders
461 and 462 and a dlrectional coupler 420 on the same
principle as mentioned above to a receiver. A phased array
antenna with a plurality of such antennas arrayed as shown
in Fig. 4B has a wide-angle radiation characteristic,
dispenses with the diplexer and the circulator, and is free
from disagreement between transmission and reception beams.
In this case, reference numeral 42 is a directional coupler,
43 a phase shifter 43. A transmitter 47 is connected to
phase shifters 43 throuyh a power divider 44b~ For
reception, the outputs of phase shifters are app]ied to a
receiver 66 after combining by a power combiner 44a.
The one side-shorted microstrip antenna for use ln the
present invention has already been proposed (Haneishi, et
al., "On Radiation Characteristics of One Side Shorted
Microstrip Antenna," '83 National Convention of Institute o~
Electronics and Comm~nication Engineers of Japan, Pro-
ceedings No. 3, pp 7A3, the Institute of E]ectronics and
Communication Engineers of Japan, March 5, 1983). In this
antenna the radiation conductors used are as small as about
one-halE that an ordinary microstrip antennas, and conse-
quently, the microstrip antenna of the present invention can
be miniaturized.
(Embodiment 2)
Fig. 2 illustrates a second embodiment of ths present
invention, in which short-circuiting conductors 281 through
284 are provided between rectangular one side shorted
micros-trip radiation conductors 211 through 214 and a
conducting ground plane (a plane 24 not shown but provided
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at the back sLde of the dielectric plane similarly to the
conducting ground plane 14 in E'ig. lB), in addition to
shor-t-circuit:Lng conductors 221 through 224. ~eference
numerals 231 through 234 are feeding poin-ts feeding through
feeders not shown. The short-circuiting conductors 281
through 284 shown to be pin-t~pe but may also be replaced
by short-circui-ting pla-tes, solder, or electrolytic
plating. With the short-circuiting pins, a rnicrostrip
antenna of excellent impedance matching can easily be
implemented. When the influence of mutual coupling is
present, the axial ratio may sometimes be degraded, but the
provision of the short-circuiting pins permits correction oE
phase, and hence makes it possible to obtain a microstrip
antenna of an excellent axial ratio.
~Embodiment 3)
Fig. 3A illustrates another embodiment in which the
radiation conductors 111 -through 114 in Embodiment 1 are
partly cut away to prepare radiation conductors 311 through
314. The present invention is applicable as well -to such
radi.ation conductnrs. In this case, reference numerals 331
to 334 are feeding poin-ts feeding from its back side b~
feeders not shown; and 35 a dielectric plate.
(Embodiment 4)
Fig. 3B illustrates another embodiment in which short-
circuiting pins 381 through 384 are providecl in Embodiment
3. The present invention is equally applicable to such a
configuration.
As described above, according to the present invention,
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a small/ lightwelght and easy-to-manufacture microstrip
antenna which is capable of si.multaneously transmitting and
receiving circularly polari~ed waves oE -two frequencies can
be implemented by arranginy two pairs of one side shorted
microstrip antennas of different si~es, that is, a total of
four microstrip antennas, on the same plane.
By employing such an antenna as one element of a phased
array antenna, a small, two-frequency separate feeding type
antenna for circularly polari~ed waves, which has a wide-
angle radiation characteristic, can be implemented on thesame plane.
Incidentally, if the short-circuiting sides of the
microstrip antenna by electrolytic platin~ or the like, then
the antenna of the present invention could easily be fabri-
lS cated through use of a conventional printed-board manu-
facturing step.
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