US3680108A - Self-steering array repeater - Google Patents

Abstract

A self-steering phased antenna array repeater system in which signals from a distant source at two spaced receptors are relatively shifted in phase and combined in a square law mixer. The output mixer current is a function of their phase difference and indicates the direction in which the signals arrive. This current is used to bring the phase of received signals together for combining and to introduce the same phase difference but of opposite sign for re-radiation by applying the current as the control for at least one injection locked oscillator which produces a phase shift according to the same function as the mixer output.

Description

United States Patent Osborne 5] July 25, 1972 [54] SELF-STEERING ARRAY REPEATER Primary Examiner-Benjamin A. Borchelt [72] Inventor: Thomas Lawrence Osborne, Holmdel, NJ. g'y 'gggg grzfii' s i g Jr [73] Assignee: Bell Telephone Laboratories, Incorporated,

Murray Hill, NJ. [57] ABSTRACT [22] Filed: June 9, 1970 A self-steering phased antenna array repeater system in which [211 App] 44 715 signals from a distant source at two spaced receptors are relatively shifted in phase and combined in a square law mixer. The output mixer current is a function of their phase dif- 1 "343/10o Tn, 343/ 1 A ference and indicates the direction in which the signals arrive. [51] luLCl. ..H01q3/26 This cum-em is used to bring the phase of received signals [58] Field of Search ..343/ 100 TD, 117 A together for combining and to introduce the same phase ference but of opposite sign for re-radiation by applying the [56] References cued current as the control for at least one injection locked oscilla- UNITED STATES PATENTS tor which produces a phase shift according to the same function as the mixer out ut. 3,394,374 7/1968 Weiss ..343/100 TD p l 1 Claims, 4 Drawing Figures E sin wt LIM.

AMP E sin out.

@E 207 E sin wt IE cos wt UTILIZING /E Sirllwflfi) L az gE g RF OUT Mggs l OSCILLATOR RECEIVED SQUARE SIGNALS LAW MIXER 22 l DETECTOR REMOTE INJECTION J I 28 29 LOCKED STATION OSCILLATOR 4 23 SOURCE 1 21 V27 RF IN TRAN FATTTED wt SIGNALS PATNIEDIIII 25 I972 3.680.108

SHEET 3 UF 3 FIG. 3

cIRcuLAToR- A0 Y DIPLEXER Esm wt m REcEIvER IF OUT V E sin w t I3 MODULATOR a4 34a.

TRANSMITTER d RECEIVER MODULATOR Bgci'I E Js cB LOCAL 05c.

I I 15 IN Al E5111 (DIF't Y Esin(wt+) i ISSSS'I A T EIR l4 5 I. ,25 24 9o (1) EsIn(oo t-) MIXER 2k DETECTOR INJECTION INJECTION TRANSMITTER LOCKED LOCKED MODULATOR OSCILLATOR OSCILLATOR Bl/ II RECEIVER 28/ \29 wS J E? LOCAL osc. ESm' l I An I I L BACKGROUND OF THE INVENTION This invention relates to self-steering array repeaters and more particularly to radio communication systems of the type employing an antenna array that automatically transmits radio waves in the direction in which waves are received from a remotely located source.

In the prior art, self-steering performance has been achieved by a series of mixing and filtering operations including a pilot signal which bears a phase characteristic indicating the direction of the remote source. Certain modifications of this system eliminate the pilot and rely entirely upon the carrier as it is received in adjacent antenna elements. These modifications, however, generally include the restriction that the retransmitted frequency be the same as the frequency of reception without extra frequency conversion steps. Other schemes use mechanically or electrically variable phase shifters to introduce the proper phases for combining and for retransmission. These phase shifting circuits are slow acting and the systems employing them are generally not capable of full diplex operation, i.e., continuous and simultaneous transmission and reception. Further, the phase shifters are a substantial source of radio frequency loss and when included in the receiving path become a source of loss not easily overcome by amplification. Further, specifically designed and relatively complicated control circuits are required to drive the phase shifters.

SUMMARY OF THE INVENTION In accordance with the invention a self-steering system is provided requiring no pilot signals, no phase shifters of the usual type, and capable of full diplex operation at different transmission frequencies. It has been recognized that if the signals from a distant source at two spaced receptors are shifted relative to each other by 90 and mixed in a square law detector, the output current will be a sine function of their phase difference and will indicate the direction in which the signals arrive at' the receptors. This current is then used to bring the phase of received signals together for combining and to introduce the same phase angle but of opposite sign to transmitted signals for reradiation toward the source. In accordance with a preferred embodiment, injection locked oscillators are used to produce the receiving and transmitting phase shifts and since these oscillators produce a phase shift according to the same sine function as the mixer output current, they are inherently compatible therewith.

Thus, an injection locked oscillator is included in the coupling paths between the antenna elements and the common output for received signals in all but one path, which is considered the reference path. Similar oscillators are included in each of the coupling paths other than the reference path between the common source for the transmitted signal and each radiating element of the antenna array. The injection locked oscillator may be included directly in the path as a special form of variable phase shifter or included indirectly in the path as the local oscillator supplying a particularly phased signal to a modulator interposed in the path.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating a self-steering antenna array repeater system in accordance with the invention;

FIG. 2 illustrates circuit details of the square law mixer-detector and the injection locked oscillators for the circuits shown as blocks in the system of FIG. 1;

FIG. 3 is a block diagram illustrating a self-steering array repeater in accordance with a second embodiment of the invention; and

FIG. 4 represents a modification of the polarity connections of FIG. 2 as required in the embodiment of FIG. 3.

DETAILED DESCRIPT ION It is known that when a radio signal impinges upon an antenna array, the portions of the wave intercepted by the elements of the array differ in phase by amounts dependent on the angle of incidence and the location of the elements in the array. These waves must be brought into a common phase before they can be combined in a common output. Furthermore, in order to transmit a radio wave of the same or nearly the same frequency from the array in the direction of the source of the impinging wave, reciprocity dictates that the phase difference between the individual signals radiated from the antenna elements must be equal in magnitude to and opposite in sense from the phase difference between the portions of the incoming wave intercepted by the antenna elements.

Referring now to FIG. I, a system of this type is illustrated by an array of equally spaced nondirective receiving and radiating antenna elements A,,, A, to A,,, all being fed oblique ly by radio waves 10 from remote station 11. Provided the radiating elements are identical, uniformly fed, and there is no interaction among them, it is known that the phase difference (1) between adjacent elements, the spacing d between them and the steering angle 0 determined by the direction of propagation are related as =(21r/)\) dsin 6 where A is the wavelength.

FIG. 1 illustrates the circuits connected to elements A and A,, it being understood that other elements A have circuits identical to A, as represented by the box 12. For convenience, operation of the invention will be explained in terms of only the signals received and transmitted on elements A,, and A,, it being understood that the same functions are duplicated separately between A and each of the other elements, such as A,,. Since the signal received and transmitted on element A is assumed to be the one with which the phase of the other signals is compared, it will be referred to as the reference signal and may be designated E sin wt, where w is the angular frequency of the carrier. It will further be convenient to designate the signal received on A, as the directed signal" indicating that it includes the phase term 5 representing direction or E sin(wt While the signal may carry intelligence in the form of frequency modulation, no term is included to represent this modulation in order to simplify the mathematics which follows.

Elements A and A, are connected to suitable diplexers, which may, for example, be circulators l3 and 14, respectively, which separate the received waves from those to be transmitted. The outputs from the second ports of circulators l3 and 14 are respectively applied to limiter-amplifiers l5 and 16 which insure that the signal amplitudes are relatively constant with time. The primary coupling path for receiving the directed signal can then be traced from the second or receiving port of circulator 14 to amplifier 16, through an injection locked oscillator 20, by which it will be brought into a common phase with the reference signal on bus 28, where it is combined with the reference signal from circulator 13 and amplifier 15 for delivery at R.F. OUT to a common apparatus 22 for utilizing the received signals. The primary coupling path for transmitting the directed signal can similarly be traced from R.F. IN and the common source 23 of the transmitted signals. Thus the signals to be transmitted are first divided into portions on bus 29 with one portion for each radiating element. One such of these portions is delivered to injection locked oscillator 21 by which it is shifted in phase relative to the reference signal and then coupled to the third or transmitting port of circulator 14. The path for the one portion comprising the reference signal extends from RR IN to the transmitting port of circulator 13.

The control path on the other hand includes a square-law mixer-detector 24 connected to receive a sample of both the reference signal and the directed signal. Thus, a sample of the reference signal is coupled through a fixed degree phase shifter 25 which converts its form to E sin(wl 90) or E cos wt. This phase shifted sample of the reference signal, which is now nearly in quadrature with the directed signal E sin(mt is then fed along with a sample of the directed signal to mixer-detector 24 which combines the two samples, squares them and delivers a rectified output direct current to buses 26 and 26a. The nature of mixer 24 and the equations which govern its operation will be given in detail hereinafter. For the present, however, assume that it derives a signal that is a given function of (i) such that current on buses 26 and 26a is a function of (b and is applied to control the operation of injection locked oscillators 20 and 21. The phase shifted reference signal from phase shifter 25 is also fed to identical circuits connected to other antenna elements A as shown by bus 27.

The nature ofinjection locked oscillators 20 and 21 and the equations which govern their operation will be given hereinafter. For the present, however, assume that both oscillators produce a change in the phase of the signal through its primary path that is proportional to the control current on bus 26 or 26a. Since this current is a function of 4:, the shift introduced by oscillator 20 can be made being that required to cancel the phase shift term in the directed signal so that it becomes E sin ml and may be combined in phase on bus 28 with the reference signal and with the outputs of other circuits 12. Similarly, the phase shift of oscillator 21 can be made being that required to convert the signal from R.F. IN to E sin(wl 4)) so that it will be directed upon radiation by element A toward station 11. Circuits l2 similarly introduce uniquely different phase shifts to the transmitted signals to be radiated by antenna elements A each in response to the difference in the phase of the directed signal received by that antenna element and the phase of the received reference signal on antenna element A Referring now to FIG. 2 the circuit details of typical embodiments for square-law mixer-detector 24 and for locking oscillators 20 and 21 are shown. In the form illustrated, detector 24 is a balanced mixer and includes a pair of square law diodes d and d These diodes may typically be Shottky barrier diodes or any ofa number of other general purpose rectifying diodes. Diodes d, and d are fed in push-pull by transformer 41 having the signal E sin(wt 4)) applied thereto and in parallel by transformer 42 having the signal E cos not applied thereto. Resistors 43 and 44 having a sum resistance R comprise the respective diode loads and capacitors 45 and 46 comprise radio frequency bypass filters.

Resistances 43 and 44 are each much smaller than the diode resistances so that the current in each resistor is essentially equal to its associated diode current. Since the diodes follow a square law, these diode currents are in turn proportional to the square of the voltages e, and 0. applied to the diodes. Thus. the net output voltage is the difference between the individual diode contributions and can be expressed Note further that h E cos wt E sin(w! +l and Substituting Equations (3) in Equation (2), expanding, and dropping all terms which cancel:

e=K,Rsinqb. it remains now to convert the voltage e into a current. Whilc numerous ways will occur to one skilled in the art, a preferred embodiment ofthe invention employs a single operational amplifier or do amplifier stage having a high input impedance and a low output impedance. Further, it is preferred that separate amplifiers 47 and 48 be provided to separately drive each of the injection locked oscillators 20 and 21. The output voltage s of each amplifier (this being the voltage on bus 26 or bus 26a of FIG. 1) can then be expressed as c K sin d:

where K is a constant including the gain of the amplifier.

Consider now the nature of injection locked oscillators 20 and 21 which are identical. Either may be an oscillator of any type having a free running frequency which can be controlled electrically and which is also capable of being synchronized or locked by a further signal applied to it having a frequency different from but within what is referred to as the locking range of the free running frequency. In accordance with a preferred embodiment of the invention, oscillator 21, which will be considered by way of illustration, may be one employing an IMPATT (impact Avalanche and Transit Time) diode 51 as described in the paper The lMPA'I'T Diode A Solid State Microwave Generator," 45 Bell Labs Record I44, May 1967 or in the copending application of B. C. DeLoach, Jr. et al., Ser. No. 883,898, filed Dec. 10, 1969, or in the copending application of B. Glance, Ser. No. 812,04l, filed Apr. l, 1969.

Capacitor 53 and choke inductance 54 represents the required decoupling circuit between bias sources and the radio frequency circuit. The injected signal input for locking is applied to the first port 56 of circulator 55 which couples it to the radio frequency circuit of diode 51 illustrated schematically by the dotted inductance 52 coupled to the diode and to the second port 57 of circulator 55. The output power is taken from the third port 58 of circulator 55.

IMPATF diode 51 when biased to the proper operating point by bias source 50 (in series with the voltage e from amplifier 48) has the relation AI Alb/K (7) between a change Aw in the natural resonant frequency w and the change AI in the bias current where K, is a constant diode parameter.

When the oscillator is synchronized byan injection signal E sin wt as supplied over input 56, the output 58 will comprise a signal having the same frequency to as the injection signal but displaced therefrom by a phase d which depends directly upon Aw according to the relation sin (Po 8 where Q is the external circuit 0 of the oscillator, G is the ratio of the output power to the injected power of the oscilla tor. Thus, changing the magnitude of the bias current through diode 51 has the effect of shifting the phase of the output signal relative to the injected signal.

Note, however, that this bias current includes a fixed component due to source 50 and an incremental component due to c The fixed current is proportional to the voltage from source 50 and is adjusted to set the natural resonant frequency w to equal that of the injection signal in the absence of an incremental current, i.e., when e is zero. The incremental current from Equation (6) is A, T Rt:

where R,, is the equivalent d.c. resistance of the diode bias circuit. Substituting Equations (7) and (9) in Equation (8) leads to sin tp" sin 1p. (Hi) It is then a simple matter to proportion all constants enclosed within the brackets of Equation (10) so that the bracketed portion equals unity. Thus, sin qb sin This means that the sine function current derived from mixer-detector 24 is exactly the function required to cause injection locked oscillator 58 to introduce the phase shift required as described with reference to FIG. 1. The sign of the introduced phase shift depends upon the particular kind of diode employed. Typically, as with IMPA'IT diodes, the phase shift will have the same sign as Ai meaning that the natural resonant frequency increases with bias. Thus, the connection as indicated by the polarity designations on amplifiers 47 and 48 are proper to obtain a negative or phase delay. Reversing these connections would produce a positive 45 as required in an embodiment to be described hereinafter. Oscillator 20 is identical to oscillator 21 and similarly shifts the injected signal by 1),, equal to Since the sine function current is ambiguous for angles greater than :90", the number of elements in the antenna array and the distance d between them should be selected according to Equation (1) so that need not exceed i90 for the required steering angle.

From the foregoing description of the broad features of the invention, it should be apparent that the invention involves substantial advantages over prior art systems. For example, no particular qualities, such as a pilot, are required of the signal from the remote station 11. Further, the invention is capable of full diplex operation. While illustrated for convenience as using the same frequency for transmission and reception, it is obvious that the injection locked oscillators 20 and 21 need not operate at the same frequency and that proper scaling thereof and of amplifiers 47 and 48 allows transmission and reception at frequencies removed from each other as required in practice.

The system of FIG. 1 has, however, certain limitations stemming from the fact that the locking or injected signal for the locked oscillators 20 and 21 comprises the intelligence bearing signal itself. Equation (8) and the factor G thereofindicate that the amplitude of the injected signal must be con stant for a given phase shift leading to the use of limiting amplifiers l and 16 and precluding the use of amplitude modulation on the carrier. Further, since injection locked oscillators 20 and 21 are interposed directly in the primary receiving and transmitting paths, they will have the effect of somewhat limiting the modulation index of a frequency or phase modulated carrier.

These limitations are eliminated in the embodiment shown in FIG. 3. Essentially, the improvement stems from the fact that the injection locked oscillators are isolated from the primary signal paths by modulators and their locking signals are derived independently from stable oscillators. This feature allows substantial flexibility in choice of both the receiving and transmitting frequencies and further allows the output and input frequencies to be at an IF frequency without a further frequency conversion stage.

For convenience, corresponding reference numerals have been used in FIG. 3 to designate components corresponding to those of FIG. 2. The principal difference will be seen to reside in the directed signal coupling paths wherein receiving modulator 30 is now interposed in the receiving path from element A, and a transmitting modulator 31 is interposed in the transmitting path thereto. These modulators are both of the form typically employed as the up and down converters in high frequency equipment. The signal corresponding to the usual local oscillator is, however, derived from the output of injection locked oscillators 32 and 33, respectively. As illustrated, each oscillator 32 and 33 has an output frequency that is different from the desired receiving and transmitting frequency by the required IF frequency. These transmitting and receiving frequencies may be selected independently of each other. This independence as well as frequency conversion to IF are, however, additional features and not necessary limitations of the system. If the transmitting and receiving frequencies are greatly different from each other, array scaling or separate antenna arrays may be required as described in an article Self- Steering Array Repeaters, by C. C. Cutler et al in The Bell System Technical Journal, September 1963, page 2,013.

The locking signals for injection locked oscillators 32 and 33 are respectively supplied by receiving and transmitting local oscillators 34 and 34a having fixed amplitudes and stable frequencies equal to the desired output frequency of the respective locked oscillator. The natural resonant frequency of each locked oscillator 32 and 33 is controlled by the voltage on buses 26 and 26a as described above (a function of the phase differential 4) of the signals received by element A and A,).

The reference signal coupling paths include receiving modulator 3S and transmitting modulator 36 in the paths to element A in order to convert to and from the IF frequency, if required, but not to introduce any change in phase. Modulators 35 and 36 are supplied by local oscillator power derived from the same sources 34 and 34a respectively, noted above which, however, are shown in order to simplify the drawing as separate sources.

Employing the signal notation developed in connection with FIGS. 1 and 2, E sin to! is received by element A and applied to modulator 35. E sin(wt is received by element A, and applied to modulator 30. Local oscillator 34 will have a frequency w where w a) is the IF frequency m The output from locked oscillator 32 will be E sin(w t (12 and mixed in modulator 30 with E sin(wt (1)), the difference product delivered to bus 28 will be E K sin [(19 w t+ d) (0 where K, is the conversion constant. Making d; equal to 4: the output of modulator 30 is E K sin (o t. The same conversion, but without phase change, takes place in modulator 35 becoming E sin m t so that the outputs from modulators 30 and 35 will be combined coherently on bus 28 with the outputs from similar circuits in box 38.

In the transmitting path it is necessary to introduce a phase shift to the directed signal that is opposite in sign to that introduced by the receiving path. Referring for the moment to FIG. 4, this reversal may be obtained in several ways including a reversal of the polarity connection of the voltage 2 to the operational amplifier 48a which drives the transmitting injection locked oscillator 33 so that signal from amplifier 48a is e,,, the reverse of e from amplifier 47 and from amplifier 48 of FIG. 2. Thus, E sin w,,.-t is received on IF IN and divided on bus 29. Transmitting local oscillator 34a will have a frequency (w to where 00 is the desired transmitting frequency. Thus, the frequency of the reference signal radiated by element A will be converted to the transmission frequency as E sin m without phase change by modulator 36. The output from locked oscillator 33 will be in the form E sin [(w w t 4)] and when mixed in modulator 31 with E sin (o t, the sum product radiated by element A, will be E K, sin(w -t as required for retransmission in the same direction as the signal received.

Separate injection locked oscillators 32 and 33 have been used for convenience of explanation and because their inclusion provides a preferred degree of frequency flexibility. However, it should be noted that receiver modulator 30 and transmitter modulator 31 may be fed by the same injection locked oscillator provided that the desired transmitting and receiving frequencies are not greatly different and provided that modulator 31 is adapted by known design to invert the phase of the carrier signal relative to the oscillator signal as compared to these phases in modulator 30.

In all cases it is to be understood that the above-described arrangements are merely illustrative of a small number of the many possible applications of the principles of the invention. Numerous and varied other arrangements in accordance with these principles may readily be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. High frequency directional apparatus comprising a plurality of antenna elements arranged in an array,

means for coupling each of said elements to a common apparatus for utilizing signals received obliquely by that element of given frequency and phase,

means for coupling each of said elements to a common source of signals of given frequency and phase to be radiated by that element, said coupling means for all but one of said elements having associated therewith an individual locked oscillator having a natural resonant frequency that is different from the frequency of the signal locking that oscillator whereby the phase of that signal being coupled is shifted from the given phase ofthat signal, and means for controlling said natural resonant frequency in response to the difference in the given phase of the received signal from that element being coupled and the phase of the received signal being coupled from said one element. 2. High frequency radio apparatus comprising at least two antenna elements arranged in an array,

means for shifting the phase of a portion of the signal received on one of said elements by 90 relative to a portion of the signal received on the other element, means for mixing said portions, means for dividing a signal to be transmitted into portions, means responsive to the difference product from said mixer for changing the phase of one of said divided portions relative to another, and means for radiating said phase changed divided portion and said other divided portion separately by said elements. 3. High frequency radio apparatus comprising at least two antenna elements arranged in an array,

means for shifting the phase of a portion of the signal received on one of said elements by 90 relative to a portion of the signal received on the other element, means for mixing said portions, means responsive to the difference product from said mixer for changing the phase of the remaining portion received on one of said elements, and means for combining said phase changed remaining portion and the remaining portion received on the other ofsaid elements. 4. High frequency radio apparatus comprising at least two antenna elements arranged in an array,

means for deriving a signal that is a given function of the phase angle between a portion of the signal received on one of said elements relative to a portion of the signal received on the other element including a square-law mixer and including means for applying said received portions to said mixer in quadrature, means for dividing a signal to be transmitted into portions, means responsive to said function for changing the phase of one ofsaid divided portions relative to another, and means for radiating said phase changed divided portion and said other divided portion separately by said elements. 5. High frequency radio apparatus comprising at least two antenna elements arranged in an array,

means for deriving a signal that is a given function of the phase angle between a portion of the signal received on one of said elements relative to a portion of the signal received on the other element,

means for dividing a signal to be transmitted into portions,

means responsive to said function for changing the phase of one of said divided portions relative to another comprising an injection locked oscillator and including means for controlling the natural resonant frequency of said oscillator in response to said function,

and means for radiating said phase changed divided portion and said other divided portion separately by said elements.

6. The apparatus of claim 5 wherein said injection locked oscillator has its locking signal input connected to receive said one divided portion and its output coupled to one of said radiating elements.

7. The apparatus of claim 5 including a high frequency mixing circuit interposed in the path of said one divided portion and wherein said injection locked oscillator supplies a signal to be mixed in said mixer with said divided portion,

8. The apparatus of claim 5 including a second mixing circuit and a second injection locked oscillator responsive to said function for changing the phase of the remaining portion received on one ofsaid elements, and

means for combining said phase changed remaining portion and the remaining portion received on the other of said elements.

9. High frequency radio apparatus comprising at least two antenna elements arranged in an array,

means for deriving a signal that is a given function of the phase angle between a portion of the signal received on one of said elements relative to a portion of the signal received on the other element, means responsive to said function for changing the phase of the remaining portion received on one of said elements,

means for combining said phase changed remaining portion and the remaining portion received on the other of said elements,

means for dividing a signal to be transmitted into portions,

means responsive to said function for changing the phase of one ofsaid divided portions relative to another,

and means for radiating said phase changed divided portions and said other divided portion separately by said elements.

10. The apparatus of claim 9 wherein said means for deriving includes a square-law mixer and means for applying said portions to said mixer in quadrature so that the output of said mixer is a sine function of said phase angle and wherein each ofsaid means for changing phase comprise an injection locked oscillator having a bias current for controlling the natural resonant frequency of said oscillator supplied by the output of said mixer.

11. The apparatus of claim 10 including a high frequency mixing circuit interposed in the path of one of said remaining portions and one of said divided portions and wherein said injection locked oscillator supplies a signal to be mixed in said mixer with said portions.

Claims (11)

1. High frequency directional apparatus comprising a plurality of antenna elements arranged in an array, means for coupling each of said elements to a common apparatus for utilizing signals received obliquely by that element of given frequency and phase, means for coupling each of said elements to a common source of signals of given frequency and phase to be radiated by that element, said coupling means for all but one of said elements having associated therewith an individual locked oscillator having a natural resonant frequency that is different from the frequency of the signal locking that oscillator whereby the phase of that signal being coupled is shifted from the given phase of that signal, and means for controlling said natural resonant frequency in response to the difference in the given phase of the received signal from that element being coupled and the phase of the received signal being coupled from said one element.

2. High frequency radio apparatus comprising at least two antenna elements arranged in an array, means for shifting the phase of a portion of the signal received on one of said elements by 90* relative to a portion of the signal received on the other element, means for mixing said portions, means for dividing a signal to be transmitted into portions, means respOnsive to the difference product from said mixer for changing the phase of one of said divided portions relative to another, and means for radiating said phase changed divided portion and said other divided portion separately by said elements.

3. High frequency radio apparatus comprising at least two antenna elements arranged in an array, means for shifting the phase of a portion of the signal received on one of said elements by 90* relative to a portion of the signal received on the other element, means for mixing said portions, means responsive to the difference product from said mixer for changing the phase of the remaining portion received on one of said elements, and means for combining said phase changed remaining portion and the remaining portion received on the other of said elements.

4. High frequency radio apparatus comprising at least two antenna elements arranged in an array, means for deriving a signal that is a given function of the phase angle between a portion of the signal received on one of said elements relative to a portion of the signal received on the other element including a square-law mixer and including means for applying said received portions to said mixer in quadrature, means for dividing a signal to be transmitted into portions, means responsive to said function for changing the phase of one of said divided portions relative to another, and means for radiating said phase changed divided portion and said other divided portion separately by said elements.

5. High frequency radio apparatus comprising at least two antenna elements arranged in an array, means for deriving a signal that is a given function of the phase angle between a portion of the signal received on one of said elements relative to a portion of the signal received on the other element, means for dividing a signal to be transmitted into portions, means responsive to said function for changing the phase of one of said divided portions relative to another comprising an injection locked oscillator and including means for controlling the natural resonant frequency of said oscillator in response to said function, and means for radiating said phase changed divided portion and said other divided portion separately by said elements.

6. The apparatus of claim 5 wherein said injection locked oscillator has its locking signal input connected to receive said one divided portion and its output coupled to one of said radiating elements.

7. The apparatus of claim 5 including a high frequency mixing circuit interposed in the path of said one divided portion and wherein said injection locked oscillator supplies a signal to be mixed in said mixer with said divided portion.

8. The apparatus of claim 5 including a second mixing circuit and a second injection locked oscillator responsive to said function for changing the phase of the remaining portion received on one of said elements, and means for combining said phase changed remaining portion and the remaining portion received on the other of said elements.

9. High frequency radio apparatus comprising at least two antenna elements arranged in an array, means for deriving a signal that is a given function of the phase angle between a portion of the signal received on one of said elements relative to a portion of the signal received on the other element, means responsive to said function for changing the phase of the remaining portion received on one of said elements, means for combining said phase changed remaining portion and the remaining portion received on the other of said elements, means for dividing a signal to be transmitted into portions, means responsive to said function for changing the phase of one of said divided portions relative to another, and means for radiating said phase changed divided portions and said other divided portion separately by said elements.

10. The apparatus of claim 9 wherein said means for derIving includes a square-law mixer and means for applying said portions to said mixer in quadrature so that the output of said mixer is a sine function of said phase angle and wherein each of said means for changing phase comprise an injection locked oscillator having a bias current for controlling the natural resonant frequency of said oscillator supplied by the output of said mixer.

11. The apparatus of claim 10 including a high frequency mixing circuit interposed in the path of one of said remaining portions and one of said divided portions and wherein said injection locked oscillator supplies a signal to be mixed in said mixer with said portions.

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