ANGULAR ERROR DETECTING DEVICE

Abstract: All components of arriving polarized waves are ob­ tained independent of the type and amount of polarization. A higher mode detector (2, 3) outputs two higher mode components which are in orthogonal relation. These two components are combined so as to maintain the orthogonal relation. A circuit is provided having a set of at least one 90° phase difference plate (4) and one 180° phase difference plate (5) which have rotatable phase lag surfaces and which are cascade-connected. The 90° phase difference plate (4) is provided on the side of the circuit combining the two higher order components. The output of the 180° phase difference plate (5) is divided into first and second orthogo­ nal polarization components. The first polarization com­ ponent is synchronously detected with a local oscillator (9) output synchronous with (Δy) reference signals to provide a first angular error output while the output of the second polarization component is synchronously detected with si­ gnals shifted 90° in phase from the local oscillator (9) output to thereby provide a second angular error output (Δx) or­ thogonal to the first angular error output.

Description: ANGULAR ERROR DETECTING DEVICE BACKGROUND OF THE'INVENTION The present invention relates to an angular error -# detecting device utilizing an antenna for receiving radio signals from a target and in which the directional angular error between the direction of the antenna,# and the direction of the target is detected. In the case where a polarized-wave from a target has a constant polarization such as polarization or linear polarization, a simple method has been known in the art to detect the directional angular error and a variety of angular error detecting devices-us-ing this technique have been put to practical use. However, recently it has been required to provide an angular error detecting device which operates satisfactorily even in the case where a target emits or reflects waves which have a nonconstant polarization such as'eliiptical polarization or which have a polarization inclination which changes with time. This device is intended for use in a system of compensating cross polarization due to rain, etc. in the propagation path. Fig. 1 shows an example of a conventional angular error detecting device of this type. In this device, a signal from a target is received by an antenna 1, and only a high order mode component excited in a circular waveguide is picked up by higher mode couplers 2 and 3. The higher mode couplers 2 and 3 are connected in an orthogonal relation. The couplers 2 and 3 are, for instance, a TE ol mode coupler and a TM 01 mode coupler, respectively. The polarization configuration and polarization plane of the fundamental mode component are converted by polarization converters 4 and 5. In this example, the converteYs--- 4 and S are a 900 phase difference plate (PDP) and a 1800 phase difference plate S, respectively. The signal subjected to polarization conversion is separated into two polarization components Exc and Eyc which are orthogonal to each other by a polarization coupler 6. -The component Exc is a main polarization component and the component E is an orthogonal polarization component. The component E is coupled to a phase locked loop (hereinafter referred to as "a PULL") at one input of a phase detector (hereinafter referred to as "a PSD") 7, a loop filter 8 and a voltage-controlled oscillator (hereinafter referred to as "a VCO") 9. The output of the VCO 9 is maintained different by 90 in phase from the component Exc On the other hand, the component Eyc is subjected to detection by a PSD 17 using the output of the VCO 9 as a reference. The output of the VCO 17 is applied through an amplifier 18 to an electric motor 19 to drive the aforementioned polarization converter S and to drive the polarization converter 4 through a gear box 20. The higher mode components from the higher mode couplers 2 and 3 are combined by an orthogonal polarization composer 33. The output of the composer 33 is applied through polarization converters 4 and 5 to a polarization coupler 36 where it is divided into two orthogonal components EXD and EYD. These components are subjected to synchronous detection by PSD's 37 and 48 using the output of the VCO 9 directly and the output of the VCO 9 applied through a 900 phase shifter 10 as references. The outputs of the PSK's 37 and 38 are applied to low-pass filters 38 and 48 so that only dc components are obtained. As a result, two angular error voltages QX and AY are provided. The above-described operation will be further described using mathematical expressions. Fig. 2 is a diagram showing relationships between a target; a tracking antenna with the angular error detecting device as described above and a polarized wave. In Fig. 2, reference character E designates the tracking antenna with the device and T the target. A coordinate system is used having as its origin the intersection of the central axis of the beam of the antenna and a plane including the target T. In Fig. 2, an angle ## between EO and ET is the angular error of the tracking antenna and a value @ is an angle corresponding to the orientation of the angular error and the inclination of the latter with respect to the X-axis. With respect to the configuration of arrived polarized waves as shown in Fig. 2, and "Emax" represent the major axis electric field and the minor axis electric field of elliptical polarized waves respectively, and "&gamma;" is the inclination of the direction of the electric field E with respect to the X-axis. max In the case where the tracking antenna is provided with the angular error detecting device as shown in Fig. 1 under the conditions as shown in Fig. 2, the electric fields EXA and and EYA at the input of the polarization converter 4 can be represented by the following expressions: EXA = Emax cos &gamma; - j Emin sin &gamma; (1) EYA = Emax sin &gamma; + j Emin cos &gamma; The values EXA and EYA are the X component electric field and the Y component electric field at the point where the values EXA and and EYA are determined after the X-Y coordinate in Fig. 2 is moved in the direction OE. The same is applicable to EXB, EYBX, EYC, EXD and EYD. If the angles of the polarization converters 4 and 5 are represented by &alpha; and ss, respectively, then EXC and EYG are: EXC =-Emax sin (&alpha; - 2ss) sin (&alpha; - &gamma;) +Emin cos (&alpha; - 2ss) sin (&alpha; - &gamma;) -jEmaX cos (&alpha; - 2ss) cos (&alpha; - &gamma;) +jEmen sin (&alpha; - 2ss) cos (&alpha; - &gamma;) (2) EYC =-EmaX cos (&alpha; - 2ss) sin (&alpha; - &gamma;) -Emin sin (&alpha; - 2ss) sin (&alpha; - &gamma;) -jEmax sin (&alpha; - 2ss) cos (&alpha; - &gamma;) +jEmaX cos (&alpha; - 2ss) cos (&alpha; - &gamma;) In the case where the device shown in Fig. 1 receives a linearly polarized wave, the relation a = 2ss should be established by the gear box. In this case, control for &alpha; = &gamma; is automatically carried out by the PSD 17, the amplifier 18 and the motor 19. In this operation, EXC = - j Emax (3) EYC = j Emin. The angular error signals outputted by the higher mode couplers 2 and 3 are combined by the orthogonal polarization composer 33 into EXB and EYB. These can be expressed as follows, when ae is small, EXB = k##{Emax cos (y- < ) - j Emin sin (Y (4) EYB - k¯0{Emax sin (y-f) - j Emin sin (&gamma;-#), where k is a proportional constant. The angles of the polarization converters 34 and 35 are the same as those of the polarization converters 4 and 5, i.e. &alpha; and ss. Therefore, under the conditions &alpha; = 2ss and a- y the outputs EXD and EYD of the polarization coupler 36 are: EXD = kA6#min sin# - j Emax cos#} (5) EYD = kµ{EmaX sin# - j Emin t Therefore, if only a component of the output EXD, which is in phase with the output EXC, is detected by PSD 37, the following expression (6) is obtained: EMI6.1 Similarly, if only a component of the output EYD which is orthogonal to EXC is detected by the PSD 47, then the following expression (7) is obtained: : EMI6.2 The values #X and #Y riven by the expressions (6) and (7) are components in the X direction and in the Y direction, respectively, of the angular error as, as is apparent from Fig. 2. In the case where the device as shown in Fig. 1 is used to receive circularly polarized waves, the polarization converters 4, 5, 34 and 35 are not driven and a is set to -Tr/4 and ss is set to zero. In this case, EMI6.3 Therefore, EMI6.4 Detecting EXD with the PSD 37 and the PSD 47 with EXC as a reference, EMI7.1 are obtained. In this case, the armature of a switch 41 in Fig. 1 is connected as shown, and in the case of a linearly polarized wave, the armature is set to the EYD side. As is apparent from the above description, in the system shown in Fig. 1, the angular error voltages X and Y are obtained by suitably switching the angular error detecting circuit according to the conditions of received polarized waves. However, the circuits in the device in Fig. l must be switched separately according to whether circuilarly polarized waves or linearly polarized waves are being received. That is, the device is disadvantageous in that, when polarization of the arriving waves alters quickly, not only the operation becomes intricate, but also it is difficult to maintian signal reception satisfactorily. In other words, the device suffers from a drawback in that all the components of arrived polarized waves cannot be obtained for Exc. For instance, if a counterclockwise circularly polarized wave arrives while the device is receiving a clockwise circular polarized wave, then EXC = 0 occurs (Emax = Emin in the expression (8)). In this case, the device may not be able to receive the signal. SUMMARY OF THE INVENTION The invention is intended to eliminate the abovedescribed difficulties accompanying a conventional angular error detecting device. More specifically, an object of the invention is to provide an angular error detecting device in which the polarization converters are suitably controlled for any arriving polarized wave, and the effects of angular error signal control are eliminated, whereby signal reception is maintained satisfactory and stable angular error voltages are provided. Specifically, the invention provides an angular error detecting device in which reference signals are obtained from fundamental mode components in a wave guide which passes a first of at least one 180 phase difference plate andat least one 90 phase difference plate, the phase lag surfaces of which are disposed so that a polarization loss of a unit adapted to receive waves from a target is minimized Angular error signals are obtained utilizing two higher mode components which are orthogonal one another, and the angular error signals are subjected to synchronous detection using a local oscillator output synchronous with the reference signals to thereby detect orthogonal angular errors. In accordance with one aspect of the invention, a circuit for obtaining the angular error signals includes at least higher mode detector means for obtaining the two higher mode components which are in orthogonal relation, a circuit for combining the two higher mode components, a circuit having a second set of at least one 90 phase difference plate and one 180 phase difference plate which have rotatable phase lag surfaces and are cascade-connected. The 90 phase difference plate in the second set is provided on the side of the circuit for combining the two higher order components. The phase lag surface of the 90 phase difference plate of the second set is disposed in an angular ratio of 2 : 1 with respect to the phase lag surface of the 180 phase differece plate of the first set while the phase lag surface of 180 phase difference plate of the second set is disposed in an angular ratio of 1 : 1 with respect to the phase lag surface of the 180 phase difference plate of the first set. The output of the 180 phase difference plate of the second set is divided into first and second polarization components which are orthogonal to each other. The first polarization component is subjected to synchronous detection with the local oscillator output which is synchronous with the reference signal to produce a first angular error output and the second polarization component is subjected to synchronous detection with a signal shifted in phase 90 with respect to the local oscillator output to thereby provide a second angular error output which is orthogonal to the first angular error output. In accordance with another aspect of the invention, a circuit for obtaining the error signals includes at least higher mode detector means for obtaining the two higher mode components which are in orthogonal relation, a circuit for combining the two higher mode components such that they are in orthogonal relation, and at least one second 180 phase difference plate. A phase lag surface of the second 180 phase difference plate is disposed in an angular ratio of 1 : 1 with respect to the phase lag surface of the first 180 phase difference plate. The output of the second 180 phase difference plate is divided into first and second polarizatinn components which are orthogonal to each other. The first polarization component is detected synchronously with the local oscillator signal output synchronous with the reference signals to provide a first angular output while the second polarization component is synchronously detected with a signal shifted 90 phase from the output of the local oscillator to provide a second angular error output which is orthogonal to the first angular error output. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing an example of a conventional angular error detecting device; Fig. 2 is an explanatory diagram showing the positional relationships between a target and an antenna provided with-such an angular error detecting device for a description of the operation of an angular error detecting device of the invention; Fig. 3 is a block diagram of a first preferred embodiment of an angular error detecting device of the invention; Fig. 4 and 5 are explanatory diagrams showing relations in polarization between reference signals for a description of the operation of the device of the invention; Fig. 6 and 7 are explanatory diagrams showing relations in polarization between error signals; Fig. 8 and 9 and 10 are block diagrams showing other preferred embodiments of angular error detecting devices according to the invention; and Fig. 11 and 12 are explanatory diagrams showing relations in polarization between error signals in the embodiment of Fig. 10. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first preferred embodiment of an angular error detecting device according to the invention will be described with reference to Fig. 3. Circuit elements having the same reference numerals as those in Fig. 1 have the same functions. The fundamental mode components are obtained at the terminal EXC To accomplish this, a PLL is formed and a signal having a phase difference of 90 is obtained as the output of the VCO 9 in synchronization with EXC In accordance with the invention, the outputs of PSD's 17 and 27 are applied through amplifiers 18 and 28 to electric motors 19 and 21 to control the rotations of the lagging surfaces (hereinafter referred to as "phase lag surfaces") of the 90 phase difference plate 4 and the 180 phase difference plate 5 in such a manner that the cross polarization terminal output EYC of the polarization coupler is minimized when a polarized wave arrives, whereby a reference signal EXC having a reduced polarization loss is obtained. The operating principle of the circuitry in Fig. 3 will be described. In order to simplify the above-described general expressions (2) for EXC and EYC, an assumption is made as follows: Emax = E cos 6 (12) Emin = E sin #. Then, Exc = E {-sin(&alpha;-&gamma;) sin( -2S -j cos(&alpha;-&gamma;) cos ( - 2ss;6)} (13) EYC = E(-sin(&alpha;-&gamma;) cosea-2ss-6) +j cos(&alpha;-&gamma;) sinfÅa-2ss+6)}. In the expressions (13), EYC is obtained with EXC as a reference. Then, the following expression (14) is obtained: EMI13.1 One of the conditions for the imaginary part of the expression (14) to become zero is for &alpha; = &gamma;. In Fig. 3, EYC is detected with the output of the VCO 9, which is different by 90 in phase from EXC in the PSD 17. With the polarization converter 4 driven by the motor so that the output is zeroed, then the condition is satisfied. With a y, the expression (14) can be rewritten as follows: EMI13.2 Therefore, if EYC is detected with the output of the VCO 9 which has a phase difference of 90 by the phase shifter 10, i.e. a signal in phase with EXC in the PSD 27, and the polarization converter S is driven by the motor 21 so that the detection output is zeroed, then the condition a-26+d = 0 which zeroes the expression (15) is obtained. When two conditions &alpha;=ss and a-2Bfd = 0 are met, then EXC = -j E, and the fundamental mode components of the arrived wave are all obtained at the terminal EXC It is evident that EYC,is zero. Thus, when an arbitrarily polarized wave arrives, all of the fundamental mode components are obtained at the terminal EXC, thus eliminating the drawbacks of the conventional system. On the other hand, if the -angles of the 900 phase difference plate 34 and the 1800 phase difference plate 35 in the angular error signal circuit are made equal to those of the 900 phase difference plate 4 and the 1800 phase difference plÅate 5 in the reference signal circuit, respectively, then it is difficult to obtain angular error signals with respect to a target in the case of an arbitrarily polarized wave. Therefore, the 900 phase difference plate 34 and the 1800 phase difference plate 35 are placed in a particular angular relation as described below so as to automatically track an arbitrarily polarized wave. The polarized wave in Fig. 2 is maintained unchanged even at th-e point a in Fig. 3. Fig. 4 shows an elliptically polarized wave at the point a which is decomposed into a circularly polarized wave of counterclockwise rotation 71 there- inafter referred to as "a CCW circularly polarized wave 71") and a circularly polarized wave of clockwise rotation 72 (hereinafter referred to as "a CW circularly polarized wave 72"). If in Fig. 4 the electric field of the CCW circularly polarized wave 71 is represented by E1a -and the electric field of the CW circularly polarized wave 72 is represented by E2a, ¯then at the angleyfrom the X-axis, E la E1 E2a = E2' (16) where E1 = (Emax + Emin)/2 E2 = (Emax + Emin)/2. (17) If the set angle (phase lag surface) a of the 90#o. phase difference plate 4 is: : (18) then the polarization state at the point b is such that the CCW circularly polarized wave 71 and the CW circularly polarized wave 72 are converted into a linearly polarized wave E lb as indicated at 73 and a linearly polarized wave E 2b as indicated at 74, respectively, EMI15.1 As the waves 73 and 74 are in phase, the composite wave 75 thereof is a linearly polarized wave. If the composite wave 75 is represented by E#b, then EMI16.1 The angle of inclination T from the X-axis is: T = y-- 45 +-p, (21) where EMI16.2 If the set angle ss of the 180 phase difference plate 5 is: EMI16.3 then the polarized wave at the point c will be a linearly polarized wave propagating along the X-axis as indicated at 76. Fig. 5 shows the polarization conditions of the CCbt circularly polarized wave 71 and the CW circularly polarized wave 72 at the point c. The waves 71 and 72 are converted into waves 77 and 78, respectively, and the composite wave 76 thereof is a linearly polarized¯wave propagating along the X-axis. If the composite wave 76 is represented by Ee, then EMI16.4 E# is an angular reference signal and is equal to Exc Higher mode components orthogonal to each other are detected by the high mode couplers 2 and 3, respectively, and are then subjected to orthogonal polarization composition in the orthogonal polarization composer 33, as a result of which a polarized 'wave is obtained which is decomposed into a CCW circularly polarized wave Eld as indicated at 81 in Fig. 6 and a CW circularly polarized wave E 2d as indicated at 82. That is, reference numerals 81 and 82 designate the polarized waves-at the point d. At an angle (y-+) from the X-axis, Eld = k AGE1 (25) E2d = k AGE2. If the set angle a of the 900 phase difference plate 34 is: a' = a + p, (26) then at the point e the waves 81 and 82 are converted into linearly polarized waves Ele and E2e as indicated at 83 and 84, respectively. The waves Ele and B2e have phases and amplitudes-- as indicated by the following expressions (27): EMI17.1 These waves are applied to the 1800 phase difference plate 35 set at an angle ss1. If ss' = ss then the polarization conditions at the point f are as shown in Fig. 7. In Fig. 7, reference numerals 87 and 88 designate waves which are obtained by subjecting the waves 83 and 84 to conversion by the 180 phase difference plate 35. If these waves 87 and 88 are represented by Elf and Ezf, then EMI18.1 If the 900 phase difference plate 50 is set at 90 , then at the point g, EMI18.2 Elg and E2g. represent linearly polarized waves which propagate on the X-axis and the Y-axis, respectively. Therefore, if wave separation is effected by inclining the polarization coupler 36 by 45 in such a manner as to satisfy the following expressions (32) and (33) EMI18.3 then EMI18.4 When the real part of the expression c34? of EX,D is detected-hy-the PSD 37 and is applied to the low-pass filter 38, then AX as indicated by -the following expression (36) can be obtained: EMI19.1 Similarly, with the real partofthe expression (35) of EY,D detected by the PSD 47 and applied to the low-pass filter 48, then AY as indicated by the following expression (37) is obtained: : EMI19.2 That is, the expression (36) describes a control signal indicating an amplitude proportional to cos f in the case of an antenna directional error direction f , while the expression (37) describes a control signal indicating an amplitude proportional to sin f . That is, the expressions (36) and (37) provide control signals indicating amplitudes proportional to X- and Ydirection errors,-respectively. In the expression (26), p is p = 2ss - y - 135 , (38) where a is indicated by the expression (18) and ss is indicated by the expressions (23) and (21). Therefore, the set angle a' of the 900 phase difference plate 34 is: a' = 2ss - 450 (39) Thus, by setting the angle of the 900 phase difference plate 34 at twice the angle of the 1800 phase difference plate 5 and by setting the 180 phase difference plate so as to have a rotation angle relation of 1 : 1 with the 1800 phase difference plate 5, the signals indicated by the expressions (36) and (37) are obtained. The stationary 90 phase difference plate 50 and the polarization coupler 36 in Fig. 3 act as a so-called circularly polarized wave generator forming an angle of 450 therebetween. Instead of this arrangement, an arrangement as shown in Fig. 8 may be employed to achieve the same object. In Fig. 8, reference numeral 36 designates a polarization coupler, 51 a 1800 hybrid a typlcai example of which is a magic T", and 52 a 900 phase shifter. If, in the above-described example shown in Fig. 3, the 900 phase difference plate 34 and the 1800 phase difference plate 35 in the angular error signal circuit are set at angles as described below, then the stationary 900 phase difference plate 50 can be eliminated. The stationary 900 phase difference plate 50 has a function of causing the polarization component 78 to lag by 90 . Therefore, if the 900 phase difference plate 34 in Fig. 3 is turned through an angle which is larger by 450 than the angle ndicated by the expression (26) or (39), i.e. &alpha; is &alpha; = 2ss, (40) then the components Eie and E2e at the point e are as follows: EMI21.1 If the 1800 phase difference plate 35 is set at an angle which meets the following expression: ss = ss + 22.50 , (42) then the components Elf and E2f at the point f are linearly polarized waves as indicated at 87 and 88 in Fig. 7 and have phases and amplitudes as indicated by the following expressions (43) and (44): : EMI21.2 With these signals subjected to wave separation by the polarization coupler 36 inclined 450 in such a manner as to satisfy the following expressions (45): EMI21.3 then EMI21.4 EMI22.1 That is, AX and AY can be obtained by processing the expressions (36) and (37) with a signal which is obtained by applying E (the expression (24)) to a (-s/43 phase shifting circuit. In the above-described embodiment, the polarization conversion circuits for processing anarbitrarilypolarized wave in the reference signal circuit are the 90 phase difference plate provided closer to the mode couplers and the 1800 phase difference plate provided after the 90 phase difference plate. Even if the 1800 phase difference plate is provided before the 90 phase difference plate as shown in Fig. 9, an arbitrarily polarized wave can be processed satisfactorily. The circuit of Fig. 9 is obtained by exchanging the positions of the 90 phase difference plate 4 and the 1800 phase difference plate 5 in Fig. 3. ln the circuit of Fig. 9, the conditions for minimizing the signal reception level of EYC are as follows: If the set angles of the 90 phase difference plate 4 and the 180 phase difference plate 5 are represented by &alpha;" and ss", respectively, then the conditions for minimizing EYC are: : &alpha;" = # + 45 (48) ss" = is + 90 . (49) From equations (49) and (23), ss ##ll, t50) Thus, the set angles of the 900 phase difference plate 34 and the .1800 phase difference plate 53 in the error circuit in Fig. 3 are determined solely by ss in any of the above-describedt embodiments. Therefore, it is evident that the set angles of the. plates 34 and 35 in Fig. 9 may be the same as those of the plates 34 and 35 in Fig. 3. Furthermore, it is also evident that even if the com ponents 50 and 36 in Fig. 9 are arranged as in Fig. 8,-or even if the element 50 is eliminated and the components 34 and 35 are set as defined by the expressions (40) and (42), the same function is obtained. In the above-described embodiments, each of the 900 phase difference plate 34 and the 1800 phase difference plate 35 in the angular error circuit may have a rotational ratio of 1 : 1 or 1 : 2 with resepct to the angle of rotation of the 1800 phase difference plate in the reference signal circuit. This control can be readily carried out with a mechanical device such as a gear train or an electrical apparatus using a synchro and a motor. Furthermore, in the abovç-described embodiments, the phase lag surfaces of the 900 phase difference plate and the 1800 phase difference plate are controlled by rotating them with motors. However, if phase difference plates using ferrite elements are employed, then the phase lag surfaces Scan be similarly controlled by electrical signals. As is apparent from the above description, according to the invention, the 900 phase difference plate in the angular error signal circuit is set to a rotational ratio of 1 : 2 with respect to the angle of rotation of the 1800 phase difference plate in the reference signal circuit, while the 1800 phase difference plate in the angular error signal circuit is set to provide a ratio of 1 : l with respect to the angle of rotation of the 180 phase difference plate in the reference signal circuit. Therefore, the angular error detecting devise of the invention can detect angular error signals with a high accuracy while effectively receiving and processing waves of any polari zation. Accordingly, the device of the invention is suitable as an angular error detecting device which automatically tracks a rocket or a satellite the radio waves from which. have large polarization variations. In addition, the device of the invention can be effectively employed for a high frequency bands where the polarization is liable to be affected, for instance, by rain during proparation. A further embodiment of the invention will be described with reference to Fig 10. In this embodiment, the position of the 90.0 phase difference plate 34 and the 1800 phase difference plate 35 are exchanged and the 900 phase difference plate 50 is omitted from the Fig. 3 embodiment;. In this case, if the set angle #' of the 180 phase difference plate 35 is: a' = ss + 22.5 , (51) then at the point e, circularly polarized waves 83 and 84 which are in phase with each other at an angle of-# + p from the X-axis are obtained through conversion. As the waves 83 and 84 have passed through the 180 phase difference plate, they are rotated in a direction opposite to that of those at the point d. That is, the wave 81 is converted into the wave 83 which is a CW circularly polarized wave, while the wave 82 is converted into the wave 84 which is a CCW circularly polarized wave, as shown graphically in Fig. 11. If the waves 83 and 84 are represented by E le and E2e'# then at the angle + p from the X-axis Ele = k /# E1 (52) P 2e = k IG P2 The waves 84 and 84 are applied to a 90 phase difference plate whose phase lag surface is at an angle a1 &alpha; ;' = 45 , (53) then at the point f the wave 83 is converted into a linearly polarized wave Elf as indicated at 87 in Fig. 12, and the wave 84 is converted into a linearly polarized wave E 2f as indicated at 88. These linearly polarized waves Elf and E2f propagate along with the X-axis and the Y-axis, respectively, and have phases and amplitudes as indicated by the following expressions: EMI26.1 If the polarization coupler 36 is inclined, for instance, by 450 to conduct wave separation in such a manner as to satisfy the following expressions, EMI26.2 In each of the expressions (56) and (57), the term e j4 is for a fixed phase of 45', and therefore it can be readily corrected. Thus, EMI27.1 When the real part of the expression (58) of EX'D is detected by the PSD 37 and is applied to the low-pass filter 38, then x as indicated by the following expression is obtained. EMI27.2 Similarly, when the real part of the expression (59) of EY'D is detected by the PSD 47 and is applied to the low-pass filter 48, then Y as indicated by the following expression is obtained. EMI27.3 That is, in the case of an antenna angular direction of f , the expression (60) describes a control singal indicating an amplitude proportional to cosf , while the expression (61) describes a control singal indicating an amplitude proportional to sin °.

Claims: CLAIMS: 1. An-angular error detecting device in which reference signals are obtained from fundamental mode components in a waveguide which have passed a first set of at least one 1800 phase difference plate and one 900 phase difference plate, t phase lag surfaces of which are disposed so that a polarization loss of a unit adapted to receive waves from a target is minimized, angular error signals are obtained utilizing two higher mode components which are in orthogonal relation, and said angular error signals are subjected to synchronous detection by a local oscillator output synchronous with said reference signals thereby to detect two orthogonal angular err6rs', the improvement wherein a circuit for obtaining said angular error signals comprises: : at least higher mode detector means for obtaining said two higher mode components which are in orthogonal relation; a circT,::it for combming said twO higher-mode components in such a manner that said two higher mode components are in orthogonal relation; ; a circuit having a second set of at least one 900 phase difference plate and one 1800 phase difference plate which have rotatable phase lag surfaces and are cascadeconnected, said 900 phase difference plate in said second set being provided on the side of said circuit for combining said twò higher order components, said phase lag surface of said 900 phase difference plate in said second set being disposed in an angular ratio of 2 : 1 with respect to said phase lag surface of said 180? phase difference plate in siad first set, and said phase lag surface of said 1800 phase difference plate in said second set being disposed in an angular ratio of 1 : 1 with respect to said phase lag surface of said 1800 phase difference plate in said first set; means for dividing an output of said 1800 phase difference plate in said second set into first and second polarization components which are orthogonal to each other; means for synchronously detecting said fiTst-polariza- tion component with said local oscillator output synchronous with said reference signals to provide a first angular error output; and means for synchronously detecting said second polarization component with a signal different by 900 in phase from that in providing said first angular error output so as to provide a second angular error output which is orthogonal to said first angular error output. 2. An angular error detecting device in which reference signals are obtained from fundamental mode components in a waveguide which have passed at least one first 1800 phase difference plate and one 900 phase difference plate, phase lag surfaces of which are disposed so that the polarization losses in reception of a unit adapted to receive a wave from a target is minimized, angular error signals are obtained by utilizing two higher. mode¯components which are in orthogonal relation, and said angular error signals are subjected to synchronous detection with said reference signals thereby to detect two orthogonal angular errors, the improvement wherein a circuit for obtaining sa-id r angular error signals comprises; ; at least higher mode detector means for obtaining said two higher mode components which are in orthogonal relation; a circuit for combining said two higher mode components in such a manner that said two higher mode components are in orthogonal relation; at least one second 1800 phase difference plate, a phase lag surface of said second 1800 phase difference plate being disposed in an angular ratio of 1 : 1 with respect to said phase lag surface of said first 1800 phase difference plate; means for dividing an output of said second 1800 phase difference plate into first and second polarization components whichare orthogonal to each other; means for synchronously detecting said first polarization component with said local oscillator output synchronous with said reference signals to provide a first angular error output; and means for synchonously detecting said second polarization component with a signal different by 900 in phase from that in providing said first angular error output so as to provide a second angular error output which ts orthogonal to said first angular error output. 3. An angular error detecting device characbetized and second higher mode couplers coupled in series with one another in an orthogonal relation; an adjustable 900 phase difference plate having an input coupled to an output of said second higher mode coupler; an adjustable 1800 phase difference plate having an input coupled to an output of said first 900 phase difference plate; a first polarization coupler receiving an output of said first 1800 phase difference plate for separating said output into a main polarization component and an orthogonal polarization component;afirst phase detector receiving on a first input said main polarization component; a loop filter receiving an output of said first phase detector; a voltage controlled oscillator receiving an output of said loop filters, an output of said voltage controlled oscillator being coupled to a second 'input of said first phase detector; a second phase detector receving on a first input said orthogonal polarization component and on a second input said output of said voltage controlled oscillator; an amplifier receiving an output of said second phase detector; a motor operated in response to an output of said amplifier to adjust said first 900 phase difference plate; a 900 phase shifter receiving said output of said voltage controlled oscillator; a third phase detector receiving on one input said orthogonal polarization component and on a second input an output of said 900 phase shifter; a second amplifier receiving an#output of said third phase detector; .a second motor operating in response to an output of said second amplifier for adjusting a position of said first 1800 phase difference plate, wherein said first 900 phase difference plate and said first 1800 phase difference plate are adjusted by said first and second motors, respectively, such that lagging surfaces of said first 900 phase difference plate and said 1800 phase difference plate are adjusted so that said orthogonal polarization component is maintained at a minimum value; an orthogonal polarization composer receiving as inputs higher mode components from said first and second higher mode couplers; a second 900 phase difference plate and a second 1800 phase difference plate coupled in series with one another; a second polarization coupler receiving an output from said series-coupled second 900 phase difference plate and said second 1800 phase difference plate, said second polarization coupler providing a wave separation of 45 ; a fourth phase detector receiving on one input said output of said 900 phase shifter and on a second input a first output of said polariza- tion coupler; a first low-pass filter receiving an output of said fourth phase detector for outputting an X-axis error signal; a fifth phase detector receiving on one input said output of said voltage controlled oscillator and on a- second input a second output of said second polarization coupler; and a second low-pass filter receiving an output of said fifth phase detector for outputting a Y-axis error signal. 4. The angular error detecting device of claim 3,characterized in that said second goo phase difference plate is arranged before said 1800 phase difference plate. 5. The angular error detecting device of claim 3, characterized in that said second 1800 phasedifferenceplate is arranged before said second 90 phase difference plate. 6. The angular error detecting device of any of claims 3-5 further characterized by a third 90 phase difference plate coupled between said series-connected second 90 phase differ ence plate and said 1800 phase difference plate, and said second polarization coupler. 7. The angular error detecting device of any of claims 3-5, characterized in that said second 9O phase difference plate is set at an angle &alpha;' = 2ss and said second 180 phase difference plate is set at an angle ss' = ss + 22.5 , where EMI33.1 wherein EmaX and Emin, respectively, represent a major axis electric field and a minor axis electric field of a received ellipticailypolarized wave and y is an inclination of a direction of said major axis electric field with respect to the X'-axis.

Inventors: YOSHIKAWA, YOSHIHIKO C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1981
Main classification: G01S3
IPC codes: H01Q21, G01S3