CA2031872A1

CA2031872A1 - Mobile antenna system

Info

Publication number: CA2031872A1
Application number: CA002031872A
Authority: CA
Inventors: Kunitoshi Nishikawa; Kazuo Sato; Tomoaki Hirako; Mitoshi Fujimoto
Original assignee: Toyota Central R&D Labs Inc
Current assignee: Toyota Central R&D Labs Inc
Priority date: 1989-12-11
Filing date: 1990-12-10
Publication date: 1991-06-12
Also published as: AU635989B2; DE69020319D1; EP0432647B1; AU6788490A; DE69020319T2; US5166693A; EP0432647A3; EP0432647A2

Abstract

ABSTRACT OF THE DISCLOSURE

In mobile communications, it is required that the beam direction is maintained to track the desired direction as the mobile is moving. For such a purpose, the mobile includes an angular rate sensor mounted therein which detects the state of turn in the mobile and to control the beam direction of the antenna in accordance with the state of turn as well as the strength of radiowave received by a receiver in the mobile. Antenna elements are in the form of microstrip antenna and are arranged in plane on the same dielectric substrate. Feeding and drive circuit layers for controlling the transmission and reception at the antenna elements are stacked into a single layered unit. This enables the antenna system to be formed into a low-profile structure. The dielectric substrate of the microstrip antenna element is formed by stacking a plurality of dielectric substrate different in dielectric constant from one another.
It is thus intended that the band width of the antenna is increased and that the mutual coupling between the antenna elements is reduced to prevent the gain of the antenna from being lowered. Furthermore, the position of feed points in the antenna element are rotated against each adjacent antenna element. This can improve the axial ratio in the array antenna over a wide band width.

Description

2 ~ 3 1 & r~ ~

- MOBI LE ANTENNA SYSTEM

i3ACKGROUND OF THE INVENTION
Field of the Invention:
The present inventlon relates to an antenna system for use in mobiles ~uch as motorcars and other vehicles and particularly to such an antenna system that is suitable for tracking dependent upon the moving direction o the moblle.
Description of the Prior Art:
With rapid pro~re~s of electronic communication technlques, radiowave communication has been popular in various ~ields. Particularly, wlth miniaturization of electronic instruments such a~ transmitter-receivers and others, the spotlight of attention is now focuse~ upon mobile communication using a land mobile telephone or the like.
There is known a cellular mobile telephone sy~tem which includes a plurality of ground base statlons. ~ach of the base station~ controls the communication link between the base station and mobiles within one area. This system has been adopted in land moblle telephones and th~ e~ However, such a communication s~stem utilizing the ground base statlons can only be used in the limited area since the number of base stations cannot inflnitely be increased.
Another mobile communication system is also known which utilizes a communication satellite. The mobile ~atellite communication system is being studied into practical use in various applications since it does not have the aforementfoned limitation as in the mobile communication utili~ing the g~ound base stations and can do hi~h-quality services over a wide area of a nation scale.

~3~872 In the latter case, an antenna to be mounted on the mobile becomes one o~ very important factors. I~ the antenna cannot well operate on transmission and reception, a transmittsr receiver and associated electronic componen~s cannot well ~unction even though the~ are very high in performance.
As a mobile such as motorcar or other vehicle is mGving, the direction of the satellite will vary every moment.
Therefore, the beam direction of an antenna mounted on the mobile must be pointed to the satellite by use of any suitable tracking means.
A step track method ls popular a~ tracking methods. The step track method is adapted to maintain the beam direction to the satellite by slightly moviny the direction of the antenna at a suitable time interval so that the beam of antenna is pointed in the direction o~ a received signal.
In such mobiles as ships and aircrafts which ~o not Yary in direction very well and in which the blocking effect by any obstruction does not risa, the 6tep track metho~ is satisfactory on tracking the satellite.
However, land mobile~ are ~re~uently ~ teered and kurned with higher speeds than those of the ships and alrcrafts and radiowave from the satellite may be blocked by any obstruction such as building or the like. ~herefore, it is frequent that the step track method is not satisfactory in tracking~ Once radiowave is blocked by a utility pole or building, the mobile may miEs the satellite completely.
Even if radiowaves are being stably received b~ the mobile, the strength of received signal may vary more than neces~ary since the beam direction oE the antenna is always g 7 ~:

change~ slightly every moment to search the maximum strength of received signal.
The antenna must he as small and thln a~ po~sible since it should be mounted on the mobile. And also, the antenna must provide a low air resistance when the mobile i8 running.
Mechanically steered antenna cannot ~e miniatured since it includes a mechanical drive.
A phased arra~ antenna is known which can be electronically steered. Such a phased array antenna is suitable for use in radar system and mobile satellite communication. It is however difficult to mi~liature the entire phased array antenna. Because it requires eeding circuits including phase ~hifters, power dividers ~eedlng and others control circuits for ~he phase shifters, and so on, in order to contr~1 the atenna beam.
One of small antennas is a microstrip antenna which may be utilized as an antenn~ element in an array antenna.
However, the micro~trip antenna has a disadvant~ge that it has a narrow band width. In order to overcome such a problem, there is considered a stacked microstrip antenna to which a passive element is added to increase the band width.
To obtain the band width of 8~, the stacked micro~trip antenna requires its height e~ual to about 0.075 wavelength.
When the central frequency is 1600 MHz, it is required that the height of the antenna is about 14 mm. This is too high for the intended purpose. As the antenna element is higher, the mutual coupling is increased. As the result, it cannot perform its function sufficiently in the gain and the axial ratio.
SDK~ARY Ur ~l~ lNv~Nr 2 ~ ~ :L 8 rl 2 It is therefore an object of the pres~nt lnventlon to provide an antenna system which has the following features:
(1) The beam of an antenna can be properly controlled dependlng on the orientation of a moving mobile.
(2) The thickness of the antenna structure is so small that it can easily be mounted in the mobile.

(3) The mutual coupling beteen antenna elements is so small that it can sufficiently function as an array antenna.

(4) The good axlal ratio is obtained throughout the wide frequency range.
To thls end, the present invention provides a mobile antenna system which comprlses a phased array antenna havlng an antenna elements layer, a feeding network layer and a drive circuit layer, all of which are stacked one above another, said antenna elements layer including a plurality of radiating patch elements on a dielectric substrate, said feedin~ network layer including a ~eeding network conslsting of phase shiters and power dividers each of which is made with microstrip-line and connected to the respective one of said radiating patches, and sald drive circuit layer including drive ~ircuits or controlling the phase ln each of the phase shifter6; an angular rate sensor for detecting the turning directlon of a mobile; a receiver for detecting the strength of receive~ slgnals; and beam control means respon~ive to the results of detection in the angular rate sensor and the receiver for controlling the beam direction o ~aid antenna, whereby the beam of the array antenna can be 3teered by controlling the phase o~ each of said antenna elements depending on the orientaion of the moving mobile.
In one aspect of the present invention, the feeding ~31872 network lncludinq the phase shifters and power dividers and the drive circuit are arranged in th~ same face of the substrate which is in turn stacked together with ~lat antenna elements, permitting the entire thickne~s oE the antenna to be very thin in comparison with the conventional phased array antennas.
The on-vehicle tracking system of the present invention has such a construction as described above. The phase relative to each ~f the ant~nna elements in the array antenna is controlled by a phase control section such that a d~fferential phase between each adjacent antenna elements will be set at a predetermined value. Thus, the pattern of the array antenna can be controlled according to the antenna element spacing and the differential phase.
Such an array antenna is called "phased array antenna".
This will be briefly described below.
There is now considered herein, for example, an array antenna which comprises a plurallty o~ anteIIna elements Al to An e~ual to n in number, these el~ments being arranged in line at a space interval d, as shown in Figure 34. It is also assumed that all the Antenna elem0nts A, - An are isotropically radlatin~ elements. It is further presumed that an angle included between the array antenna arrangement and a normal line (angle of incidence) is ~ and that a plane wave reaches when the angle ~ is equal to ~ O.
As~uming that the leftmost element Al as viewed in Figure 34 is a reference element, the phase of a wave reaching each of the antenna elements A2 - A~ will advance by ~ ~ for each antenna element from the starting element A2 to the ending element An. Thus, ~ ~ is represented by:

1, 8 r~? 2.
~ ~ = 2~ (d/~ ) sin ~ O
where ~ is the wavelength o~ the incldenta:L plane wave.
If the phase in each of the antenna elements A2 - An is delayed by ~ ~ by the phase shi~ters B2 - ~n and thereafter they are combined together by a power combiner C, high frequency si~nals can be -taken out in phase from the respective a~tenna elements A, - ~". Therefore, the beam o~
the array antenna will be able to be scanned ln any direction ~ .
On transmission, the radiated power is focused in any direction ~ in the similar manner. I~ the antenna elements A
are arranged two-d~mensionally, the beam of the array antenna can he scanned in three dimensions.
The present invention is to control the beam o the antenna depending on the results of detectlon of the orientation of the mobile during turning and the received signal level from the recelver. When the mobile moves stralght, the beam dire~tion o~ the antenna will not be varied. Thus, the variations of recelvea ~ignal level can be efectively suppre~sed. On turning, the beam dlrectlon of the antenna is controlled to track the satellite well, depending on the result~ of detection in the aungular rate senæor and the received signal. When the radiowave i~ blocked by any obstruction on ground, the tracking can be effectively continued by using the angular rate sensor.
It will be apparent from the foregoing that the mobile antelma system according to the present invention can perorm the tracking very well slnce tracklng can be controlled depending on the state of the moving mobile.
Furthermore, the mobile antenna system can ef~ectively deal ~3~87~
with any challge o~ mo-tion oE the mobile since the present invention utilizes the phased arr~y antenna having the beam which can electronically be controlled.
Since the phased array antenrla section comprises the antennas, feeding networks and drive circuits which are layered one above ancther, it can be formed into a thinned structure which can be easily mounted on a small land mobile.
Microstrip antenna used as antenna elements in the array antenna comprises a ground plane, a drlver patch elemento disposed on a dielectric substrate opposite to the ground plane and a parasitic driven patch element arranged and spaced apart from the drlver patch element, the dielectric substrate being formed into a stack of two or more dielectric substrates having dif~erent dlelectric constants.
Thus, the microstrip antenna is characterized by that it is formed into a dielectric substrate located between the driver patch element an~ the ground plane, the dielectric substrate being formed by a stack of two or more dielectric materials having di~ferent dielectric constants.
In order to reduce mutual coupl1ng hetween antenna elements, it is requlred that the spacing be-tween the driven patch element and the ground plane is decreased. On the other hand, if it is wanted to widen the band width, the spacing between the driven patch element and the ground plane must be increased. However~ the matching to the impedance of the feed line cann~ be taken only by satisfying such conditions, Therefore, the band width with low VSWR does not become wide enough.
The inventors have studied such a problem ln rarious types of experiments to research the condition required to 7 ~

take the matchlng. It has been thu.s found that the band width of the antenna to be matched to the feed line .i9 changed hy varying the relative dielectric cons-tant & , between the dr~ver patch and the ground plane into the value & r ~ ~ ~
which can provide the maxi~um band width, as shown in Figure 35.
If tha relative dielectric constant is set to the value of r ~ A X ~ the w~de frequency band width can be provided as shown by solid line in Figure 22. If the resulting value &
rmnx iS equal to the value o r of a dielectric easily available (which, ~or example, is equal to 2.6 for Teflon:
3.6 ~or a dielectric material comprising bis(maleimide)~
triazine resin and glass abric; and 4.6 for glass epoxy)~
such a dielectric material can be used to realize a wide band antenna element.
It is frequent that the easily available dielectric does not have its relative dielectric constant equal ~o the value & rm~ -In accordance with t~1e present invention, thus, the microstrip antenna can have any specific inductive capacity & r substantially equal t~ the value of & rm 8~ by stacking a plurality o~ conventional dielectric materlals different in dielectric constant from cne to another into a suitable thickness.
For example, if a dielectric su~strate is formed by stacking three dielectric layers having a thickness tl, t2 and t3 and relataive dielectric constants & r 1 ~ r 2 and & r 3 repeatively, this substrate will have the entire value of relative dlelectrlc constant & r rep~esented by:
& r = (tl ~ tl ~ t,)/

2~3~72 ( tl / r ~ ~ t~/ ,z ~ t3 / r 3 ) ~
The required value ~ , can be equal to ~ r~ rl accordance with the pre~ent invention, the substrate of the driver patch element can haYe a widened ranye of the dielectric constant by stacking two or more dlelectric substrates different in relative dielectric constant from one to another and also properly ad~usting the thicknes~ of each substrate.
In such a manner, the microstrip antenna can have a frequency band width which is increased up to about 8~. At the same time, the spa~ing between the driven and driver patch elemente can be reduced in comparison with the prior art. Thus, if such microstrip antennas are u~ed as antenna elements in the array antenna, the mutual coupllng between the antenna element spacing can be redu~e~ and slmultaneously the array antenna itself can be miniaturized with hiyher function.
In accord~nce with the present in~ention, further, ~he array antenna is characterized b~ that each of th~ antenna elements has two ~eed points having dif~erent angles of 90 relative to the center and that said array antenna further comprises feed means for supplyiny ~owers with 90 phase difference to the two feed point of the antenna element to excite the circular polarization, said antenna elements being arranged into a triangle fashion and being rotate~ by 120 or feed positions different from each other by ~0 ~ .
In general, it is very difficult that only one of antennas has a good axial ratio throughout the wide frequency band.
An antenna is thus considexed herein whlch has a 8 r(~ 2 polarizatlon in the form of ellipsold as shown in ~i~ure 32.
It has been found that if two such antennas ~re arranged perpendicular to each other, that i~, if the feed points are arranged angularly rotated one another hy 90 to compensate for the strength together, a good axial ratio can be obtained as shown by broken line in Figure 33. It has been also confirmed that a good axial ratio is provided over a wide band width.
The a~ial ratio is further improved i~ the positions o~
the feed points are equally distributed in all the directions. It has been further con~irmed that the location of each adjacent antenna feed points at different positions reduces mutual couplin~ between antenna elements.
If the ~eed points in each ad~acent antenna elements in an array are differently positioned, the a~ial ratio in the entire array antenna can be improved throughout a wide frequency band. Even if each of antenna elements ha~
different feed po~ition, the antenna elements can be corrected out of phase at di~ferent feed positlons to provide a predetermined phase to each of the antenna element~.
The present invention ca~ provides a new and improved array antenna comprising a plurality of antenna element~
having different feed point positions, which can lmprove it~
ax1al ratio and e~ectivsly perform the transmission and reception over the wide frequency band.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a, schematic block diagram of one embodiment of an antenna system constructed in accordance with the present invention.

2 ~ 7 2 Figure 2 is a block diagram of a control selec~or section.
Figure 3 is a block d~agram o a turning control ~ection.
Figure 4 is a bloc~ ~iagram of a non-turning control section.
Figure 5 is a block diagram o~ a radlowave blocking control section.
Figure 6 is a flow chart illustrating the operation of the antenna system.
Figure 7 is a flow chart lllustrating the sa~ellite direction search (S2~ operation.
Figure 8 is a ~low chart illustrating the beam control (S30) operation when the radiowaves are blocked.
Fiyure 9 is a 10w chart illustrating the beam control (S40) operation when the mobile is movin~ straight.
Figure 10 is a flow chart illustrating the beam control (S5~) operation when the mobile ls turning.
Figure 11 is a perspective view of a phasQd array antenna in the first embodiment of the present invention.
Figure 12 is a perspective view of a phase shifter.
Figure 13 illustrates the operation o~ the phase shlfter.
Figure 14 is a perspective view of a power divider.
Figure 15 is a schematic cross-e~c~ion of the phased array antenna in the first embodiment.
Figure lG is a cross-sectional view of the connectlon between the phase shifter and a drive circuit in the first embodiment.
Fi~ure 17 illustrates the COnneCtiQn of the drive circuit.
Figure 18 is a schematic cross-sectional view of a phased array antenna in the second embodiment, Figure 19 is a schematic cross-section of a phased array 2~31~7~

antenna in the third embodiment.
Figure 20 is a perspective vlew of the schematic structure of a microstrip antenna relating to on~ embodiment of the present invention.
Figure ~1 is a cross-se~tional view o~ the embodiment shown in Figure 20.
Figure 22 is a graph showing variations o~ VSWR at the antenna ~eed point relative to requencies in the embodiment shown in Figures 20 and 21.
Figure 23 is a schematic top view of an array antenna to which the principle o~ the microstrip antenna shown in Figures 20 to 22 is applied.
Figure 24 is a graph showing variations of mutual coupling between antenna elements relative to fre~uencies when microstrip antenna elements accordlng to the embodiment shown in Figures 20 to 22 are arranged in a plane.
Figure ~5 illustrates the arrangement of antenna elements in the array a~tenna relating to the embodiment of the present invention.
Figure 26 illustrates the position ot feed points to the antenna elements i~ the ~ame embodiment.
F$gure 27 is a graph showi~g the a~ial ratio o~ the array antenna in the same em~odiment.
Figure 28 illustrates a phase shift clrcult for supplying power to the antenna elements.
Figure 29 illustrates a circuit ~or yenerating circular polarization.
Figure 30 illustrates the position o~ the ~eed points to antenna elements in another embodiment.
Figure 31 illustrates the arrangement o~ antenna elements 203~872 in still another embodime~t.
Figure 32 illustrates the polarization of an antenna element.
Figure 33 illustrates the polariz.ation of a comhination of antenna elements.
~ igure 34 illustrates -the principle of the phased array antenna.
Figure 35 is a graph showing the relationship between the relative dielectric constant and the band width.

DETAILED DESCRIPTION OF PREFERRED EMBO~IMENTS
Referring first to Figure 1, there is shown a mobile antenna system constructed in accordance with one embodiment of the present invention, whlch comprises an antenna 10 capable of being optionally controlled with respect to its beam direction. This antenna 10 may be in the ~orm of a phased array antenna, the beam dirsction of which can be electrically controlled by using a phase shlfter. More particularly, the antenna 10 may be a phased array antenna comprising a plurality of antenna element 10al through lOan, the number of which elements is equal to n in number.
Signals received by the antenna 10 are then ~upplied to a receiver }2. The receiver lZ performs the conventional signal processing operations such as detection, amplification and others, with the resultant signals being then fed to the conventional signal processing system. In this embodiment, however, the receiver 12 is adaptea to g~ve the strength of received signal (hereina~ter called "receiving level") to CPU
14.
In this embodiment, the t~rning detector section rJ1 2, comprises an angular rate sen~or 16 for detecting the orienta-tion angle of the mobile, tha resultant data being given to CPU 14. The angular rate sensor 16 ma~ be o~ any one of various types such as ~as rate g~ro, vibrating gyro, laser gyro, mechanical rate gyro and other~.
Although this embodiment will be de~cribed as to the angular rate sensor, any other angle sensor such as t~rrestrial maynetism sensor or the like may be used to perform the similar control.
In response to the receiving level from the receiver 12 and the angle data from the angular rate sen80r 16, the CPU
14 controls the beam o~ the antenna 10. The CPU 14 comprises five sections:
(a) Satellite Direction Search Secti~n Satellite direction search section 18 is adapted to search a direction of satellite by scanning the antenna beam receptiun mode into the ominidirection and finding the direction of the satellite in which the receiving level become~ maximum. When the antenna 10 is controlled by the satelllte direction search section 18, therefore, the satellite can be ~ound from an initial state without any information regarding to the satellite.
(b) Control Selector Section Control selector section 20 comprises three parts, that is, a receiving level reading part 20a, an angle reading part 20b and a control selecting part 20c, as seen from Figure 2. Dependin~ on the receiving level and the orientaion angle of the mobile, the control selecting part 20c selects optlmum one o~ three control parts, that is, a turning control part 22, a non-turning control part 24 and a signal blocking csntrol part 26. In such a manner, the antenna wlll be controlled.
(c) On-Turning Beam Control Section On-turning beam control section 22 comprises an angle reading part 22a, a receiving level reading part 22b, a turning direction judging part 22c, a left~hand turning beam control part 22d, a right-hand turning beam control part 22e and a phase shiEter control part 22f, as seen from Fi~ure 3. The on-turning beam control section 22 controls the beam of the antenna when the vehicle turns. More particularly, the beam of the antanna is moved to be directed to the satellite, depending on data relating to the turn direction o~ the mobile.
(d) On-Nonturnin~ Beam Control Section On~nonturning beam control section 24 comprises a receiving level reading part 24a, a beam control part 24b and a phase shi~ter control part 24c, as seen from Figure g. The on-nonturning beam control section 24 controls the antenna when ths vehicle is movin~ on gently curved and straiyht roa~s. IE the vehicle is moving straight or substanti~lly stralght, it is not basically required to c~ange the direction of beam. Thus, the on-nonturning beam control section 24 will only judge whether or not thereceiving level is equal to or higher than a predeterminedthreshold, while maintaining the direction of beam constant~
(e) On-Blocking Beam Control Section On-blocking beam control section 26 comprlses an angle readlng part 26a, a r~ceiving level readlng part 2~3:187~

2~bt a turning angle computiny part 26c, a beam controlling part 26d, a timer 26e and a phase shifter control part 26f, as seen from Figure 5. The on-blocking beam control section ~6 controls the antenna when radiowaves are completely blocked by buildings or the like. Since no signal is received ~y -the antenna in such a situation, the direction of beam in the antenna lO will be controlled by the information of the angular rate sensor 16. The direction of the satellite can be predicted from the in~ormation of the sensor 16. The beam of the antenna 10 is directed to the known direction of the satellite. However, this method may provide a wrony value in the turning angle because of accumulating angular errors. In order to avoid such a problem, the beam ls scanned in the omnidlrectlo~al direction to re-confirm the dtrectlon o~ the satellite after passage of a given time period.
The control operation of the antenna 10 in this embodiment will now be de~cribed with reference to Figure 6.
In the beginning of the operation, the satellite search section 18 first judges whether or not the direction of the satellite is unknown (Sl). Normally, the direction o~ the satellite will be searched since it is unknown (S~).
When the satellite direction is known on termination of the search (S2), the maximum receiving level and the direction of beam are stored.
When the search oE the satellite direction ~S2) is terminated or when the satellite direction has been known, the beam is pointed toward that satellite direction (S3).
Next, the control selecting section ~0 selects one of the 1 ~

2~3:1~7~

on-turni~g beam control, the on-nonturning beam con-trol and the on--blockiny beam confrol ~S5 ~ S10).
For this purpose, the recelving level reading part 20a reads a receiving level LEV of a sign~l which is received using the beam set at S3 (S4).
After obtaining a receiving leve LEV, switching level SL
and blocking level BL are determlned from the re~eiving level LEV (S5) at the control selecting part 20c.
The switching lavel SL is a reference level used when the direction o beam in the antenna 10 is to be switche~ in the other direction. When a signal is received ln a certain direction and if its receiving level LEV is lower than the switching level SL, that beam is switched to an adjacent beam. The blocklng level ~L is a level used when it is judged that the radiowave is blocked. If the receiving level LEV is lower than the blocking level TL, the tracking will be performed using on the output of the angular rate sensor 16 wbich has been rea~ into the angle reading part 20b. It should be determin~d that the ~witching level SL is the value lower than the ma~imum recei~ing level LEVMAX by a given a~ount and that the blocking level TL is substantially lower than the maximum recelving level LEVMAX.
When the switching and blocking levels (SL and BL) are determined through S4 and S5, these levels are used to control the direction of beam of the antenna 10.
If the receiving level LEV is larger than the switching level SL, this means that signal wi~h sufficient strength is received in the current direction o beam. It is thus not required to change the direction oE beam. When the receiving level LEV is larger than the value of SL, therefore, the l 7 ~31~72 reading o~ the receiving level LEV and the comparison be-tween the receiving and switchlng levels will be repeated.
1~ the receiving level LEV ls smaller than the value of SL, the directlon of beam may be changed. It is thus judged whether or not the receiving level LEV is smaller than the blocking level BL (S8).
If the receiving level LEV is smaller than the value of BL, it is judged that the radiowave fr~m the satellite is blocked. The on-blocking beam control is thus carried out (S30). Therea~ter, the process is returned to the receiving level reading step (S6).
If the receiving level LEV is laryer than the blocking level BL, it is judged that the radiowave is not blocked and that the antenna beam is in the different ~irection. The process rea~s the angle from the angular rate sensor 16 (S9).
From the comparison between the current and former angles, it is ~udg2d whether or not the mobile is turning (S10).
If it is judged that the moblle is not turnlng, the on-nonturning beam control is carried out (S~0). I~ the mobile is turning, the on-turning beam control is performed (S50). After these controls, the pxocess will return to the receiving level reading step (S6).
The descriptlon will now be made individually to the satellite search (S2), on-blocking beam control (S30), on-nonturniny beam control ($40) and on-turning beam control (S50).
Search of Satellite .. . . . .
The search of satellite (S2) will be described with reference to Figure 7.
The search of satellite direction is accomplished by the 2~3'1g~2 satellite direction search section 18 in the CPU 14. First o~
all, a value of LEVM~X which is representative of the maximum receiving level (S2~ set at zero. The dlrection of the current beam is then changed (SZ02). The process reads a receiving level LEV in the newly set direction oE beam (S203).
If the receiving level LEV is larger than the value of LEVMAX (S204), the value o~ LEVMAX is replaced to the value of LEY now sensed and the directio~ o beam at thi~ time is memorized (S205).
Untill the beam is scanned in the omnidirection, the process is repeated (S206). After the search of satellite direction has been completed, the beam is set toward the satellite ~S3).
On-Blocking Beam Control This control (S30) will be described with reference to Figure 8.
The on~blocking be~m control is accomplished by the radiowave blocking controlling section 20 in the CPU 14 This controlling section 20 computes a turning angle usin~
the information from the angular rate sensor 16, the resultant value being wsed to actuate the beam controlling part 26d such that the beam is maintained toward the satellite.
In the on-blocking beam control (S30), a value of TIMER
relatlng to time in the tim~r 26e is first set at zero S301 ~ .
Data from the angular rate sensor 16 is then read into the angular rate reading section 26 (S302), the data is used to determine the turning angle at the turning angl~ computing 2~31~72 part 2Gc (S303).
I f this value o kurning angle exceeds the anglea ~
between ad~acent two beams, the beam controlling part 26d replaces the current beam by the adjacent beam (S304, S305).
If the turning angle does not e~ceed said angle a ~ or when the beam is changed to the ad~acent beam depending on the direction of turn, a receiving level LEV in that beam direction is read in ~S306). This value o~ LEV is then compared with a switching level SL (S307).
If the value of LEV is larger than the value of SL, the beam in the current direction can perform its sufficient reception. Thus, this direction is malntained and the proce~s is returned to the reading step (S6) for reading the nex-t receiving level LEV.
If the value of LEV is smaller than the switching level SL, it is ~udged whether or not the value o TIMER is larger than a predetermined waiting time TIMELIMIT (5308~.
The process will be repeated from the angle reading step (S302) to the receiving level comparlng ~tep (S307) until this time reaches the waiting time TIMELIMIT.
Turning angle obtained ~rom the angular rat~ sensor may deviate from the actual turning angle due to ~he accumulation of any error of angular rate sensor. Thus, the waiting time TIMELIMIT should be set depending on the precision of a sensor used therein.
If the receiving level LEV dld not exceed the switching level SL within the a~orementioned time period, it is judged that the satellite is missed. The satellite seaxch section 18 is thus actuated to per$orm the satellite searching step as in S2 (S309). The proce~s is continued until the value of LEV~AX exceeds the switching value of S~ (S310). A~ the receiviny level exceeds the value of SL, the phase shiter control part 26f sets the phase shifter to change the beam in that direction. The process is returned to the receiving lèvel reading step (S6).
On-Nonturniy Beam Contr The process i~ moved ~o the on-nonturning beam control (S40) if at the step (S10), it is judged that the mobile is not in turning. The on-nonturning beam control ~S~0~ will be accomplished in accordance with such a procedure as shown in Figure 9.
Even when the mobile is moving on a straight road, the direction o~ movement in the mobile may be slightly changed.
In such a case, since the rece$ving level LEV may be lower than the switching level Sl and higher than the blocking level BL, the direction of b~am must be shifted. For such a purpose, the direction of beam is first chang~d to the left~hand ad~acent beam (S401). In this direction, a receiving level LLEV is th~n read in the receiving level reading part 24a ~S402). The beam controlling part 24b then compares the value of LLEV with the receiYing lev~l before such a changing (S403).
If the value of LLEV after beam changing is larger than the value o LEV before beam changing, it is judged that the beam is properly directed to the satellite. The process is then returned to the receiving level reading step IS6). If the value of LLEV is smaller than the value of receiv$ng level before the beam changing, it is judged that the beam is not properly directed to the satellite. The process is then performed such that the beam is changed to the ~3~g72 right-hand ad~acent beam relative to -the original direction.
A receiving level RLEV in this di~ection i8 then read in the receiving level reading part 24a (S405)~ Subsequently, the value of RLEV is compared with the previous receiving level LEV a-t the beam control par~ 24~ (5406).
If the value o RLEV is larger than the previous receivin~ level LEV, it is judged that the beam is properly directed to the satellite. The process is then returncd to the receiving level reading step (S6). If the value of RLEV is smaller than the previous receiving level LEV, it is judged that the beam is not properly directed to the satellite. Thus, the beam is returned to th~ original direction (S407). The process is repeated starting from the receiving level reading step (S6).
The beam changing operation is controlled by the phase shifter control part 24c.
On-Turnin~ Beam Control If it is judged that the mobile is now turning at the step (S10), the on-turning beam control (S50) is performed by the on-turning bea~ controlling part 14b. This will now be described with respect to Figure 10.
Judgement is ~ir~t made what direction the mobile is turned in (S501). This judgement is accomplished by the turning direction judging part 22c from the information of the anglular rate reading part 22a. I the mobile is turning rlghtward, the on-r$ght-turning beam contr~l part 22e actuates the phase shiftex part 22f so as to shift the ~eam in the antenna 10 to the left-hand adjacent beam (S502). In such a direction, a receiv1ng level LLEV is read in (S503) and then compared with the previous receiving level LEV

2~3~72 (S50~).
If th~ valu~ o~ LLEV is smaller tban the previous receiving level LEV, it is ~udyed that the b~am is not properly directed to the satellite. The beam is returned to its original direction (S505). The process is returned to the receiving level reading step (S6).
If the value of L~EV is larger than the previous receiving level LEV, the process is re-turned to the receiving level reading step (S6) while maintaining the beam direction.
If the turning direction ~udgin~ part 22c judges that the mobile is now turning l~ftward (S501), the on-left-turning beam control part 22d actuates the phase shiPter control part 22f so as to change the beam to the ri~ht~hand adjacent beam (S510). At this time, a receiving level RLEV is read in (S511) and then compared w~th the previous receiving level LEV (S512). If the value o~ RLEV is larger than the previous receiving level LEV, the procesæ i5 returned to the receiving level reading step (S6). It not so, the beam i~ returned to its original direction ~S513) whi].e the procedure is returned to the receiving level reading step (S6).
These steps S510 to S513 in the on-turning beam control (S50) are completely similar to the steps S404 to S407 in the on-nonturning beam control (S40). I~ it is ~udged at the step S501 that the mobile is turning leftward, therefore, the procedure may go to the step S404 in the on-nonturnin~ beam control (S40). As a result, the steps S~04 to S407 may be common to the steps S510 to S513.
The antenna system according to this embodiment can utilize data of the angle ~rom th~ angular rate sensor 14 to track the satellite and provide the tollowing advantages:

~1872 (a) Radlowaves ~rom satelli~e can be stably received since no changing oE beam is carried out in the case ~ stralght movement of the mobile.
~ b) The beam will not be changPd to any unnecessary direction since the angular rate sensor detects the directlon of mobile turning.
(c) Even when radiowaves are blocked, the state o~ the turning can be known by using the angular rate sensor. Since the control of beam is per~ormed depending on the sensed state of the turning, the satelllte can be continued to be substantially accuratel~ searched such that the reception will be properly re-started lmmediately after the strength of radiowave has been restored.
If the blocking of radiowave continues for a rslatively long ~ime p~riod, the omnidirectional scan is performed to re-search the satellite.
In such a manner, it can he reliably avoided that even if the satellite becomes visible, the restoration of reception is disturbed due to any error which may occur when the tracking is carried out only by the angular rate sensor.
Some examples of a phased array antenna which are preferable in the present invention will be described below.
Fi~st Example of Phased Array Antenna ... . . . .. . . . .
Figur~ 11 is a perspective view of the first example of the phased array antenna while Figure 15 is a cross-sectional view o~ this phased array antenna.
Referring first to Figure 11, the phased array antenna comprises an antenna element layer consisting of sixteen stacked microstrip antenna elements 114 which are arran~ed on the two dielectric substrates 112, 113 in the ~orm of S~ 8~:2 rectangular lattlce; and a fee~lng network layer inclu~ing phase shifters 122 an~ power dividers 124, the8e phase shifters and power dividers being arranged on the opposlte side of the dielectric substrate 120 at position~
correspon~ing to the antenna element 11~. As seen from Figure 15, the antenna element layer is closely connected to the feeding network layer throu~h ~ ground plane 116. Within an air gap 170 below the feeding network layer, there is formed a drive circuit layer which comprises a drive circult 134 and a control llne 132, these components beiny arranged on a circuit substrate 130 at a position opposed to each of the phase shifters 122. In such a manner, the antenna element, feeding network and drive circuit layers are stacked one above another in the order described herein.
Although the antenna element.~ 114 have been described as to the rectan~ular lattice arrangement, they may be arranged in any suitable configuration, for example, such as trian~ular l~ttice fashlon.
The antenna elements 114 on the two dielectric æubstrateY
112, 113 may be formed vn a copper film over the sub~trate by the use of any suitable means such as etching or the like.
In order to reduce the entire thickness of the antenna, it i~ particularly required that the feeding network i5 smaller and thinner in structure. The layout is also important.
In the first example, the phase shifters 122 and power dividers 124 on the ~eeding network layer are ma~e with microstriplines or the like which are formed on the dielectric substrate 120 over the whole surace thereof. Then, the antenna element layer may ~e closely connected to the feeding network layer through the common ground plane 116.
Radio-frequency signals may be supplied to the antenna through f~ed pin~ 126 each of whi~h connects each of the antenna elements 114 with the corresponding one of the phase shifters 122.
In this e~ample, one-point feeding is thus made ~o the antenna. ~y suitably selecting the conftguration of the antenna element 114 and ~he feeding point, the antenna may be excited of either liner polar1zation or circular polarization. A circular polarization may be excited by feediny ~0 phase different radio-frequency signals to two points having different angle of 90 relative to the center of the a~tenna element.
As shown in Fi~ure 12, each of the phase shifters 122 comprises microstripllnse 150, PIN diodes 151, bias lines 152 and connectors 136b adapted to connect with the drive circuit 134. Such a phase shiter i~ known as switch-lined phase shifter. Each oP the PIN diodes 151 ls switched by a bias cu~rent which ls supplied through the corresponding bias lina 152.
The operation of each switch-lined pha~e shifter wlll be described with re~ere~ce to Figure 13. This phase ~hi~ter is adapted to change the phase from one to another by performing the switching between microstriplines Ll and L2 different in length when bias current is applied to th~ PIN diodes 151.
The differential phase ~ at this time is represented by:
~ = 360x (Ll - L2)/~
where ~ ls a wavelength used.
As seen from Figure 12, this embodiment utilizes such an arrangement that differences between two line lengths are set 203~72 to be 45 , 90~ and 180 and that three switch-lined phase shifters 154, 155 and 15G are connected in tandem with one another to form three-bit phase shif-ters which are variable each ~5 through 360 a, The number of bits on one phase shifter depends on the granularit~ beam positions expected.
When the number o~ bit~ are increased, the granularlty of beam positions becomes small although the structure ~ecomes more complicated.
Although this embodiment has been described as to the switch-lined phase shifter, the present invention may be appl~ed to other type phase shifter, such as loaded-lined phase shifter and hybrid-coupled phase shifter.
Figure 14 shows a structure of power divider. The power divider 124 is made of microstripline which is formed on the dielectric substrate 120. The power divi~er 124 i~cludes an input/output terminal 160 through which a radio-frequency signal enters the power divider and finally distributed into 16 parts through 11 two-branch parts, thus being ~ed to the respective phase shifters 122. The input/output terminal 160 is conn~cted with a coaxial connector 161. The inner conductor o the coaxial connector 161 i8 connected to the power divider 124 while the outer conductor thereo~ is connected to the ground plane 116.
In operation, a radio-frequency sign~l inputted to the power dlvider 124 is dividQd into 16 parts each o which is inputted to the respective one o~ the phase shifters 122. At each o~ the phase shifter 122, the signal phase is varied depending on the directlon of beam and then supplied to the respective one of the radiating patches 114 through the corresponding feed pin 126. The ~ignal will be transmitted 2B3;:LgrlX~

as radiow~ve from the an~e~na elements.
Although the present invention has been d~scribed malnly as to transmission, it ma~ be similarly applied -to reception.
The circuit substrate 130 which ls the drive clrcuit la~er is disposed with the air gap 170 below the ~eding network layer. Again, the drive circuit layer comprises the drive circuit 134 ~or driving the PIN diode in the phasé
shifter 122 and the control line 132 for controlling the drive circuit ~34. It is required hers~n that ~he air gap 170 has a thickness equal to about 10 mm for preventing the property of the ~eeding netwvrk layer from degradlng due to proximit~ to the d~ive circuit la~er.
Each of the phase ~hi~ters 122 ls connected with the correspon~ing one of the drive circuits 134 through a connector 136a on the ~rive circuits 134 and another connector 136b on the phase shifter 122, as seen from Figure 16. Each of the drive circuits 134 is conne~ted to the control line 132 which is in turn connected with any external controller through a connector 139.
Each o~ the drlve c~rcuits 134 i~ ~lso connected with a controller 190, as shown in Figure 17. Command signals from the controller 190 are sent to the respective drive circuit 134 through the connector 13~. Each drive circuit 134 is connected with the corresponding one o the phas~ shifter with the six control lines corresponding to the ~5 bit 154, ~0 bit 155 and 180 bit 156.
As will be apparent from the foregoing, the present invention can provide a phased arr~y antenna which is constructed to be very thin by stacking necessary components (antenna elements, phase shifters, power dividers a~d drive circuits).
Second Example of Phased~ y~
F~gure 18 shows, in cro~s-section, the second example of the phased array antenna.
Although the first example is of such a structure that the feeding network layer is made of microstripline on the dielectric substrate 120 at one si~e, ~he second example includes a feeding network layer consistlng o phase shifters 122 and power dividers 124 which are formed in the dielectric substrate 120 by line conductors. The dielectric substrate 120 is closely interposed between two ground planes 116 and 140. ~he other parts are similar to those of the flrst example.
In the ~irst example, it is required that the air gap 170 has a thickness equal to about lO mm ~or preventing the property of the feeding network from degrading due to proximity to the drive circuit layer. Howe~er, the ~econd example, the feeding network will not be affected by the proximlty to the drive circuit layer. Thus, the air gap 170 between the feeding network layer and the drlve circuit layer is reduced. As a result, the length oE the connector 136 connecting the phase shifter 122 with the drive circui~ 134 can be decreased. This can further reduce the thickness of the phased array antenna in comparison with the fir~t example.
As in the ~lrst example, it is possible in the second example that the connector 136 is divided into two nested connector section~ 136a and 1~6b as shown in Figure 15. By nesting these connector section~, there~ore, the ~eeding network layer can easily be connected and disconnected with the drive circuit layer.

8 Y ~
Third Example o~ Phased ~rray ~ntenna Figure 19 shows, in cross-section, the -third example of the phased array antenna which is characteri~ed by that the parts mounting sur~ace of thP drive circuit layer is dispo~ed on the substra-te at the oppoæite side to the feeding network layer 120. More particularly, the underside of the circuit substrate 130 includes the driYe circuits 134 and the control lines 132. The drive circuits 134 are connected with the phase shifters 122 through pins 138.
As a result, the feeding network and drive circuit la~eræ
can be disposed closely to each other without any air ~ap therebetween. Thus, ~he entire thickness of the phase arra~
antenna can be further reduced. In this example, furthermore, the antenna can be strengthened for vibration since there is no air gap without need of connector or the like.
All the antenna~ in the first to third examples are very thin in thickness. Even if they are mounted on vehtcle's roof or the like/ their air resistance can be very small while the appearance of the vehicle will be least a~ected by the antennas.
Arrangement of Antenna Elements There will be described the structure of a microstrip antenna element which ls most preerable for using in the phased array antenna cons-tructed in accordin~ to the present invention.
Figure 20 is a perspective view of the en-tire construction of this embodiment while Figure 21 is a cross-sectional view o Figure 20. The antenna element comprises a driver and driven patch elements ~1~, 222 and a 7 ~

groundplane 212 wit~l 6tacked dielectrlc substrates. A driven patch element 222 is on a dielectric substrate 220 at a position spaced a~ay from the feed elemen~ oonductor 214 a predetermined distance. It is preerred that the gap between the driver patch element 214 and the dielectric sub~trate 220 is filled with any suitable means such as a foamed material having a small dielectric constant to maintain the entire str~ngth of the antenna.
This embodiment is characterized by that three dielectric layers 240, 242 and 244 are disposed between the ground plane 212 and the driver paatch element 214. By taking such a construction, the~e can be utilized an easily available dielectric substrates as each of the dlelectric layers while pro~idlng the desired dielectric constant u~ing three dielectric layers 240, ~42 and 244~ Although the illustrated dielectric between the driver patch element 214 and the ground plane 212 is of three-layer type, the number of layers to be stacked may be selected depending on the thickness, the relative d~electric constant and other Eactors.
This embodiment provides thr~e-layer type slnce it ca~
be manufactured more easily and changed the relative dielectric constant more broadly. It particularly determines a combination of relative di~lectric constant and thickness for providing a wide band antenna, b~ that the relative dielectric Gonstant and thickness (tl or t~) of each of the dielec~ric substrates 240 and 244 are in~ariable while the relative dielectric constan~ and thickness t2 of the dielectric substrate 242 is variable.
In this example, it is set that the central frequency operating the antenna ls ~O~ the wavelength ls ~ D ~ the ~03~8~2 radius Rl of the driver patch elem~nt 214 is nearly equal to 0.6 ~ 0; and the radius R2 o the driven patch element is nearly equal to 0.19~ 0.
~ n this embocliment, parameters required to increase the frequ~ncy band width of the antenna are experlmentally determined by settlng that the thickness t, or ta o each of the dielectri.cs substrates 240 and 244 is equal to 0~0085 ~ 0 and the relative dielectric constant ~ r iS equal to 3.6 (which values are obtalned, for example, from a dielectric substrate made o~ bis(maleimide)-triazine resin and glass fabric or a dielectric made o~ glass and thermo~etting polyphenyl o~ide) and also by varying the thickness and relative diele~trlc constant of the dielectric substrate 242.
As a result, it haq been found that the microstrip antenna of this struct~re can have a widened ~and width by staeking the dielectrics into such a confi~uration as shown in Fi~ure 20 in such a condition that the ~ r of the dielectric substrate 242 is equal to 2.6 (for example, Te~lon) and the thickness t2 thereof is equal to 0.011 ~ 0. At this time, it is taken that the relatlve dielectric constant & r oE tha dielectric substrate 220 i~ equal to 3.6; the thickness t4 thereo~ i~
equ~l to 0.0037 ~ 0 and also that the spacing g between the driver patch 214 and the dielectric substrate 222 is equal to 0.027 ~ 0.
Figure 22 shows VSWR (Voltage Standing Wavs Ratio) ~or the requency of such a microstrip antenna element. ~s seen from Figure 22, this embodiment has the band width of about 8~ which VSWR is smaller than the value 2.
Figure 24 shows the character~stic of a mutual coupling between antenna elements in the array antenna. As seen from 3 ~

~.1 g~

this figure, the mutual coupling is equal to ab~ut -30dB
within the fre~uency band ranged between 0~94Eo and 1. 06~o .
This means that the mutual coupllng between antenna elements in the antenna system o~ the present lnvention iS increased abou-t 10 dB larger than the prior art antenna systems.
In this example, lt wa~ taken that the center-to-cente~
spacing between ~ach ad~acent antenna elements i9 equal to 1/2 wavelength (~ o/2)~
The feed point to each of the antenna elements which are preferable for use in the phased.array antenna of the present invention will be described below.
Rotation of Feed Poi~t Position of ~rray Antenna This e~bodiment provides a circular polarized array antenna 300 which comprises 19 mlcrostrip antenna elements 310, as shown in Figure 25.
The antenna elements 310 are arranged into a triangle lattice ~ashion, and fed as radiation patches with a circular polarization.
The circular polarization is excited by applying radia-frequency signals with the 90 phase dif~erence to a radiating patch 316 at two feed polnts angularly ro~ated away from each other by 90 about the center thereof, through feed lines 3Z2.
For such a purpose, for e~ample, a Wilkinson circuit 330 may be utilized, as shown in Figure 29.
In this example, the Wilkinson circuit 330 is connected, at its feed end 333, with a feeding network. The Wilkinson circuit 330 includes two microstrip-line ends 330a and 330b having their lengths different from each other by 90~ , These connecting end~ 334a and 334b are connected wlth two 2~87~

feed points in the antenna element 310 such that the phase in the two feed points will be out of ph~6e by 90~ .
Such feeding may be si~ilarly made wlth the hybrid circuit or the like.
This embodlment is characterized by that the positions o~
the two feed points in each of the antenna elements is ro~ated by some degr~es ayainst the neighbor element~ More particularly, the array antenna of this embodlment has four different positions for the feed points whlch are different from one another by each 90 Q ~ as shown i~ Figure 26. The antenna elements 310a - 310d shown in Figure 25 correspond to those shown in Flgure 26 (a) - (d), respectively. The axial ratio can be improved by arranging the antenna elements 310a - 310d such that the position of two feed points in one o~ the antenna elements is different from that of any adjacent antenna element, as shown in Figure 25.
Figure 27 shows the axial ratio in ~hi~ embodiment. It is clear that the a~ial ratio i9 improved to be lower than 1.0 d~ within a wide frequency ~and. It is appear that the axial ratio of the array an-tenna ls highly improve~ as compared with the axial ratio of a single antenna element.
The antenna elements should be fed the radio-frequency signals with the phase difference corresponding to the rotation of the feed positions. For e~ample, in the case of the set of the four antenna elements as shown in Figure 26, the antenna elements should be fed the radio-requenc~
signals with 0 for the element 310d, 90 for the element 310c, 180 for the element 310b, 270 for the element as shown in Figure 28.

2Q3~72 Although the above example has been described about the set of four antenna elements having feed positions rotated by each 90 , the set of three antenna ~lements 310e - 310g can be also used.
More particularly, three antenna elements 310e - 310y having feed point positions di~erent from each other by 120 as shown in Figure 30 are arranged as shown in Figure 31.
Thus, the feed positions in each adjacent antenna elements 310 can be set to be different from each other. Similarly, this can improve the axial ratio in the entire antenna syste~.
If five or more feed point positions are arran~ed, the axial ratio can be correspondingly improved. However, it becomes di~ficult to regulate the position of feed points, and the phase shift circuits are more compl.icated. It is thus believed that it is not practical to utilize five or more Eeed point positions.

Claims

1. A mobile antenna system comprising:
a turn detecting section for detecting the state of turn in a mobile;
an antenna controllable with respect to its beam direction, a receiving section for taking a signal proportional to the strength of radiowave received by said antenna; and a beam diretion control section for changing the beam direction acording to the turning angle of the mobile detected by said turn detecting section and also the strength of the radiowave received by said receiving section.

2. A mobile antenna system as defined in claim 1 wherein said turn detecting section includes an angular rate sensor for sensing the turning angle of the mobile.

3. A mobile antenna system as defined in claim 1 wherein said beam direction control means comprises:
a satellite direction searching section for controlling the beam direction of said antenna over a broad range to obtain a higher strength in said received radiowave and to find the satellite direction: and a control selecting section for selecting one of control modes depending on said strength of received radiowave and said state of turn, said control modes selected by said control selecting section being at least three types:
(a) an on-nonturning control selected when it is judged that the mobile is moving straight and adapted to change the beam direction of the antenna slightly so as to detect the direction of the highest strength of received radiowave;
(b) an on-turning control selected when it is judged that the mobile is turning and adapted to change the beam direction of the antenna depending on the state of turn and also to select the direction of the highest strength of received radiowave, and (c) an on-blocking control selected when radiowave is blocked by buildings and trees and adapted to change the beam direction of the antenna depending on the state of turn.

4. A phased array antenna mounted on a mobile, comprising:
an antenna element layer including a plurality of radiating elements which are formed on a ground plane through a dielectric substrate with a ground plane:
a feeding network layer including a feeding network which consists of phase shifters and power dividers, these components being made of microstripline which are respectively connected with said plurality of radiating elements and disposed on a dielectric substrate; and a drive circuit layer including a drive circuit which is connected with said phase shifters in said feeding network-and adapted to supply a signal for controlling said phase shifters, said antenna element, feeding network and drive circuit layers being stacked one above another.

5. A phased array antenna as defined in claim 4 wherein each of the phase shifters in said feeding network layer made of a plurality of microstrip-lines different in length from one another, said microstrip-lines being selected to change the value of phase shift by switching means.

6. A phased array antenna as defined in claim 4 wherein said switching means operates to turn on and off PIN diodes which are formed on each of said microstrip-lines at the opposite ends.

7. A phased array antenna as defined in claim 4 wherein said phase shifters have three types of phase shift amounts corresponding to 45 ° , 90° and 180 ° .

8. A phased array antenna as defined in claim 4 wherein the power dividers in said feeding network layer are made of microstrip line.

9. A phased array antenna as defined in claim 4 wherein said antenna element lyaer and feeding network layer are shared by a common ground plane and wherein said antenna elements and feeding network layers are formed on said common ground plane at the opposite sides thereof.

10. A phased array antenna as defined in claim 4 wherein said feeding network layer is opposed to said drive circuit layer and wherein said feeding network and drive circuit layers are connected with each other through detachable connectors.

11. A phased array antenna as defined in claim 4 wherein the phase shifters and power dividers in said feeding network layer are formed by striplines in on the dielectric substrate between the ground plane on the side of the antenna layer and the ground plane on the side of the drive circuit layer.

12. A phased array antenna as defined in claim 4 wherein said drive circuit layer includes drive circuits formed on the substrate which is fixedly mounted on the ground plane on the side of the drive circuit layer.

13. A phased array antenna as defined in claim 4 wherein each of said radiating patch elements in said antenna layer includes two feed points with 90° difference in angle about the center thereof, the positions of two feed points rotated about the center thereof such that each of said radiating patch elements is excited in a circular polarization mode and wherein said radiating patch elements are arranged into a regular triangle lattice in three directions and have the set of three positions of feed points angularly different from one another by 120 degrees, the position of feed points in one of said radiating patch elements being different from that of any adjacent radiating patch element.

14. A phased array antenna as defined in claim 4 wherein each of said radiating patch elements in said antenna layer includes two feed points with 90° difference in angle about the center thereof, the position of two feed points rotated about the center thereof, such that each of said radiating patch elements is excited in a circular polarization mode and wherein said radiating patch elements are arranged into a regular triangle lattice in three directions and have the set of four positions of feed points angularly different from one another by 90 degrees, the position of feed points in one of said radiating patch elements being different from that of any adjacent radiating patch element.

15. A microstrip antenna element suitable for use in a mobile antenna system, comprising:
a ground plane;
a driver patch element disposed opposed to said ground plane through a dielectric substrate; and a driven patch element disposed spaced away from said driver patch element, said dielectric substrate being formed by stacking two or more dielectrics different in dielectric constant from one another.

16. A microstrip antenna element as defined in claim 15 wherein said dielectric stack is of three-layer structure.

17. A microstrip antenna element as defined in claim 16 wherein the two upper and lower layers in said three-layer dielectric stack are made of a dielectric substrate having the same dielectric constant and the intermediate layer is made of a dielectric substrate having a dielectric constant different from that of said upper and lower layers.