US3140490A

US3140490A - Communication system with automatic antenna beam steering

Info

Publication number: US3140490A
Application number: US169696A
Authority: US
Inventors: Sichak William; Raymond O Schildknecht
Original assignee: SICHAK ASSOCIATES
Current assignee: SICHAK ASSOCIATES
Priority date: 1961-11-30
Filing date: 1961-11-30
Publication date: 1964-07-07
Anticipated expiration: 1981-07-07

Description

July 7, 1964 W. SICHAK ETAL Filed Nov. 30, 1961 2 Sheets-Sheet 1 T RANSMITTER COMBINER RECEIVER 9 osc PHASE SHIFT A ING SIGNAL A CONTROL FILTER FIG I REC PHASE SHIFT COMBlNER PHASE SHIFT CONTROL I MODULATING SIGNAL FILTER 2 I, 4 I, 9 1/ 9- MULTI PHASE 1 MOD COUPLER SHIFT MODULATING I SIGNAL FILTER PHASE 2 W SHIFT CONTROL INVENTORS FIG 5 g a W W y 7, 1964 w. SICHAK ETAL 3,140,490

COMMUNICATION SYSTEM WITH AUTOMATIC ANTENNA BEAM STEERING Filed Nov. 30, 1961 2 Sheets-Sheet 2 PHASE MODULATED RESULTANT S|ONAL REFERENCE SIGNAL FIG.2

REcEIvER 22 l I 24 l 27 l I AM PHASE AMP E MOD SHIFT COMB DEMOD 08c CONTROL FREQ A DEMOD 26' 28 FIG. 3

I REEZE IVER I 30 32 I I FREQ PHASE FREQ 34 9' M D SHIFT COMB DEMOD I I 35 oSc w A CONTROL DEMOD INVENTORS FIG. 4 WILLIAM SICHAK RAYMOND O. SCHILDKNECHT 3,140,490 COMNIUNICATION YSTEM WITH AUTOMATIC ANTENNA BEAM STEEG William Sichalr, Nutley, and Raymond 0. Schildlmecht,

Clifton, N.J., assignors to Sichak Associates, Nutley,

N .J a corporation of New Jersey Filed Nov. 30, 1961, Ser. No. 169,696 9 Claims. (Cl. 343-100) This invention relates to an improved antenna beam steering method and apparatus in which a beam possessing directive characteristics is automatically moved or steered to face the source of a signal emanating from an unknown direction.

It is often desirable to utilize antennas or an antenna array having directive characteristics instead of one whose pattern is omni-directional since such antennas are capable of providing induced received signals of greater amplitude and because such received signals have a greater signal to noise ratio; that is, the received signal has a relatively higher informational content and lower noise content. Particularly when signals are to be received which have been transmitted from a very great distance and are subject to high fading loss and noise contamination, it is obvious that it is desirable to receive the maximum signal strength possible with the least amount of noise.

When it is necessary or desirable to use antennas having directive characteristics in a communication system in which a station must receive signals from or transmit signals to a distant station whose location is unknown, the beam should face such distant station for maximum effectiveness. The directional antenna beam must, therefore, be rotated if it does not initially face the distant station.v This rotation may be accomplished mechanically by physically rotating the antenna or by suitable electrical circuit means.

Further, in order to avoid missing a signal from an unknown location, the antenna beam must be rotated rapidly and stopped rapidly. It is not desirable to use a multiplicity of directional antenna arrays or antennas pointed at different directions because the cost is very high and the system is cumbersome.

An object of this invention. therefore, is to provide an antenna system having directional characteristics, which system is quickly responsive to a received but unknown signal to automatically steer the antenna beam to face the direction from which the unknown signal emanates.

A further object of this invention is to provide an antenna system in which the directional pattern may be rotated quickly by electrical means to point to and remain fixed at the direction fromwhich the unknown signal emanates.

A still further object of this invention is to provide an antenna system whose directional pattern is controlled by the amount of phase shift in antenna circuit which phase shift is automatically adjusted in accordance with the direction from which the unknown signal emanates.

Still another object of this invention is to provide an antenna system having a plurality of individual antennas forming a directional array, the directional pattern of which is controlled by the amount of phase shift in each of the antenna circuits and in which an external source of electrical oscillations is used to modulate the received signals, which modulation may thereafter be utilized to determine whether there is any phase shift or phase difference between the received signals and which determination may thereafter be used to inject a selected amount of phase shift in predetermined antenna circuits.

The foregoing objects may be accomplished in accordance with this invention, by providing an antenna system comprising a plurality of individual antennas which collectively produce a directive antenna pattern. Each of the antennas may have connected in their respective receiving circuits a means which will produce a variable amount of phase shift. The signals induced in respective antennas, forming the antenna outputs, may then be combined to determine whether each of the circuits contains the proper amount of phase shift which in turn determines whether the directive pattern of the antennas is pointed in the right direction, i.e., the direction from which an unknown signal emanates.

In order to make this comparison, the induced output sigal from one antenna is modulated with a constant frequency signal. This modulated signal is combined with an induced output signal from a second antenna and the modulating component of this combined signal is extracted and compared with the original modulating signal. If the induced outputs are out of phase by a phase angle 0, a resulting signal may be obtained by suitable demodulation, the magnitude of which will depend upon angle 0. This signal is utilized to inject an amount of phase shift in the first antenna circuit to reduce the phase angle and bring it to 0.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.

H6. 1 is a schematic diagram in block form of the automatic beam steering apparatus and method of this invention;

FIG. 2 is a vector diagram illustrating the manner by which the output signals induced in a pair of respective antennas are combined to produce a resulting signal;

FIG. 3 is a schematic diagram in block form of one embodiment of the automatic beam steering method and apparatus of FIG. 1, in which one of the induced output antenna signals is amplitude modulated;

H6. 4 is a schematic diagram in block form similar to FIG. 3 of the receiver and demodulator shown in FIG. 1, Where the type of modulation employed is frequency modulation;

FIG. 5 is an alternative embodiment of the automatic beam steering apparatus and method shown in FIG. 1 as adapted to receive a plurality of signals of various frequencies in a plurality of antennas.

Referring now to the drawings, there is shown at FIG. 1 an antenna system having two antennas indicated by the letter R (reference antenna) and numeral 1. Antenna R may be omnidirectional as may be antenna 1. If omnidirectional antennas are used, the directional characteristic of the array is introduced by phase shift means located in the circuit branch coupled to antenna 1. The antenna elements may be arranged in any desired manner, and a regular spacing, while desirable, is not necessary.

Each of the antenna elements is connected by a respective transmission line, the antenna 1 being connected to a modulator 2, which in turn is connected to a phase shift means 4, the output of which is applied to combining circuit means 5, the function of which is to add together the signals conducted through the antenna branch circuits.

The signal induced in antenna R is applied directly by suitable transmission lines to combining means 5.

Modulator 2 may modulate the signal from antenna 1 in any manner, such as for example by amplitude modulation, frequency modulation or phase modulation. However, for the purposes of the immediate discussion, the specific mode of modulation utilized need not be considered. The modulating frequency produced by oscillator A is applied to modulator 2 to produce a small amount of modulation on the received signal. This modulated signal is then applied to phase shift means 4. Except for the embodiment employing multicouplers, the

3 order of connection of the modulator 2 and phase shift means may be reversed. The modulating frequency produced by oscillator A can be above or below the normal output frequency band as received by antenna 1. The phase shift means 4 is capable of injecting the required amount of phase shift in a manner desicribed hereafter, which amount is normally below 360. ,As shown, the output from the phase shift means 4 is applied to combining means 5 along with the reference signal received from antenna R.

In the ideal case, the directive antenna beam will be directed along a path which is perpendicular to a line drawn between the locations of the two antennas. At this location, the amount of phase shift introduced by phase shift means 4 would normally be zero degrees. However, when a signal emanates from a direction which is not perpendicular to this line between the two antennas, the received signal is not received simultaneously at both antennas and the difference in time between the time that the first or nearest antenna receives the unknown signal and the second antenna is equal to a fractional wave length. This difference in time may be actually more than one wave length, but it will also have a fractional component such as one and three quarter wave lengths, and for practical purposes it is only the fractional wave length that produces the amount of phase shift between the received signals.

As shown in the vector diagram of FIG. 2, the reference signal may be considered as being on the horizontal axis while the modulated signal received from the output of the phase shift means 4 is initially at an angle 0. Angle represents the phase angle between the received signals because of the difference between the time in which the unknown signal is received at antenna R and antenna 1. At this time, it is assumed that the phase shift means does not introduce any phase shift.

Referring back to FIG. 1, the type of modulation produced at modulator 2 can be of any kind, depending upon the type of receiver employed. As shown, the resultant signal is applied to receiver 7. The output from receiver 7 may be utilized and applied to a modulating signal-filter 9, the output of which is applied to a phase shift control means 10.

If desirable, the same system may be used for transmission in which case receiver 7 will be disconnected from the circuit and a transmitter 11 connected at the output of combiner which in this case actually becomes the input combiner 5. An N-way hybrid coupler or impedance matching transformer will act satisfactorily as the combiner 5.

The output of modulating signal filter means or detector 9 is of the same frequency as the modulating signal produced at oscillator A, the magnitude of which will depend upon the phase difference 0 between the signals received from antennas R and 1.

The output of oscillator A is applied to modulator 2 and phase shift control means 10, the output of which controls and varies the amount of phase shift introduced by phase shift means 4. Phase shift control 10 may be so designed that it receives signals from oscillator A and filter means 9, and if there is any phase difference between these two signals, an output control function will be generated which will act to vary the amount of phase shift introduced by phase shifts means 4.

For example, phase shift control means 10 may be a reversible motor in which the output from oscillator A is applied to one phase winding, and the output from filter 9 is applied to the other phase winding. of the received signals are in phase, the reversible motor will not be caused to rotate. If there is a difference, the rotation of such motor may be used to vary an impedance element in the phase shift means 4 to produce the necessary amount of phase shift. Phase shift control 10 will continue to operate to change the amount of phase shift until the two applied signals are in phase.

Amplitude Demodulation In describing the operation of this system, it will be assumed that modulator 2 is a phase modulator (although a frequency modulator may be used alternatively) and that the modulating signal from oscillator A modulates the signal received from antenna 1 so as to vary the phase thereof in accordance with the modulating signal; as shown in FIG. 2, the reference signal and the phase modulated signal will be combined or added together in the combining means 5 to produce a resultant, which resultant will have amplitude modulation, the magnitude of which will depend upon the angle 6 between the signals initially received by antennas R and 1.

At this point it'is desirable to assume that no phase shift has been introduced by' phase shift means 4. The combined signal is applied to receiver'7 where it is demodulated and applied to the remainder of the circuit. Further, part of the signal applied to receiver 7 is applied to a modulating signal filter means 9 which is tuned to the frequency of oscillator A. The filter means 9 is an amplitude demodulator resigned to detect the phase modulation of the output from combining means 5. When 0 is not zero, the signal produced at filter means 9 will have an amplitude depending upon 0. When the received signals are in phase, there will be no output from the modulating detector and hence no phase shift is introduced. For example, if the phase shift control is a twophase reversible A.C. motor, no rotation of the motor will occur either when the two signals applied to the two stator windings are in phase, or when oneof the two signals is absent or zero. The two phase reversible motor may be caused to operate as a result of the signal received from filter means 9 alone in which case part of the modulating signalneed not be applied to either of the stator windings and other means may be utilized to obtain the in-phase condition. When this is done, the signal from filter means 9 may be divided into two paths one of which has a different impedance fromthe other and the divided signal is applied to the respective windings of the stator. If howevervfilter means 9 produced a signal indicating that there has been a phase shift, the two signals when applied to phase shift control element 10, the reversible motor will produce the necessary correction and vary the amount of phase shift produced by phase shift means 4.

This performance is similar to that obtained with a mechanically rotatable directional antenna. As the distant station producing the unknown signal moves, the change in phase of the received signal will immediately be sensed and an additional phase shift control will be applied to phase shift means 4 to shift the directional pattern produced by antennas R and 1. If it is necessary to transmit in this direction, the receiver is simply disconnected from the circuit and the transmitter is applied at the same point to which the receiver was connected leaving the introduced phase shift angle intact.

This system can operate effectively even when the signal received by one antenna element is so low that the If both normal receiver output is unusable. For example, consider a system Whose bandwidth is 4 kc. The band width of a control amplifier in receiver 7 can be 10 c.p.s. or less. Thus the noise power in the control circuits is 4,000/10, or less by a factor of 400 than the noise power in the normal output of the receiver and therefore proper operation is easily obtained.

Frequency Modulation As shown in the embodiment of FIG. 4, the signal i from oscillator A is applied to a frequency modulator 30 which modulates the received signal from antenna 1. The modulated signal is applied to phase shift means 31 and then to combining means 32 to which the signal from reference antenna R is also applied. The output from combining means 32 has an amplitude modulated component being that of the signal f from oscillator A. The

signal from combining means 32 will be applied to frequency demodulator 34 and also applied to an amplitude demodulator 35 which serves to detect the frequency modulating signal f This component f will have a magnitude depending upon the phase difference between the received signals from antenna R and antenna 1. This signal is applied to control means 33' to vary the phase shift introduced by phase shift means 31 in a manner which has been heretofore described.

It should be obvious that other types of demodulation may be used to one of the received signals and that the phase shift between the received signals may be detected and utilized by suitable circuitry added after the combining circuit.

Frequency Demodulation Referring now to the embodiment in FIG. 3, it is shown that the type of modulation applied to the received signal from antenna 1 is amplitude modulation, the modulating signal being applied from oscillator A at a frequency which may be stated as f The received signal from 1 is amplitude modulated at 22 and then applied to phase shift means 4, after which it and the reference signal received from antenna R are combined incombining means 25 and applied to receiver 26. The output from combiner 25 will be a frequency modulated signal in accordance with the frequency of oscillator A, the magnitude of which will dependupon the phase difference 0 between the signals received from antennas R and 1.

This signal may then be applied throughsuitable amplitude demodulating circuitry 27 and applied for further use. The signal from combiner 25 is also to be applied to a frequency demodulator 28 .which will detect the frequency component f of the entire combined signal. The signal at the output of frequency demodulator 28, may then be applied to an appropriate control circuit 26' to which the signal f from oscillator A is, applied and the control means 26' will operate to vary the amount of phase shift introduced into the circuitas. previously ,described.

Multiple Signal Reception The foregoing principles and circuits may be generalized further by referring to the schematic drawing, FIG. 5. In this case more than two antennas are shown and have been indicated as R, 1 and 1". Each of the antennas further may receive a plurality of signals f f etc. In each of the circuits a suitable unit known as a multicoupler or a directional filter serves to segregate the various signal components. The multi-coupler is essential when more, than onefrequency is used to obtain more than one communication channel. In this case the combining circuit 5 must necessarily be an N-way hybrid or impedance matching transformer which can serve to combine the signals of the same respective frequencies.

The output from receiver 7 is applied to filter means 9', 9" each of which may be tuned amplifiers. There are N-l such amplifiers, that is there are the same number of amplifiers less one as there are antennas.

The outputs from filter means 9, 9" are applied respectively to phase control circuits 10. and 10" respectively which in turn respectively determine and vary the amount of phase shift introduced into each circuit, in a manner heretofore described.

Having described the principles of our invention in connection with the specific apparatus heretofore disclosed, it is to be understood that this description has been set forth by way of example and not as a limitation to the claims and accordingly we wish to be limited to the subject matter as expressed in our claims as follows.

We claim:

1. An automatic antenna steering system comprising a plurality of spaced apart antennas,

a modulator,

phase shift means connected to the output of said modulator,

means to couple the output from one of the antennas to the input of said modulator,

means to combine received antenna signals additively,

means coupling the output from one of said antennas to said combining means,

means coupling the output of said phase shift means to said combiner, an oscillator producing a fixed frequency substantially different from the frequency at the received signals, the output of said oscillator being applied to said modulator, phase shift control means to control the amount of phase shift produced by said phase shift means, the output of said oscillator also being connected to said phase shift control means, receiving means coupled to said combiner, demodulating means coupled to said receiver to detect the component of modulation produced by said oscillator,

the output of said demodulator means also being connected to said phase shift control means,

said phase shift control means being adapted to compare the signal received from said oscillator and said demodulator and to control said phase shift means in accordance with the phase shift between said compared frequencies,

whereby the amount of phase shift introduced will determine the directive patterns of the antenna array. a

2. The combination defined in claim 1, in which a transmitter may be connected to said antenna circuits,

said transmitter being connected to said circuit at a point beyond the phase shift network and means to disconnect said receiver from said circuit.

3. A method of automatically rotating a directive beam produced from an antenna array and automatically fixing it to the direction from which an unknown signal emanates comprising the steps' of receiving said signal by a first antenna,

receiving said same signal by a second antenna, modulating the signal received from said first antenna at a predetermined frequency by a first mode of modulation, I combining the modulated signal with the signal received from said second antenna whereby said combined signal will have a modulation component dependent upon the modulating signal and whereby said modulating component will have a phase shift as compared with the modulating signal equal to the phase shift between the signals received at the respective antennas,

demodulating said combinedsignals by a second mode of modulation to detect the strength of said modulating signal,

and comparing the modulating signal and the said demodulated signal and thereafter controlling the amount of phase shift applied to said received signal in accordance with the compared signals, whereby said directive beam is rotated in a manner to eliminate the phase shift between received signals. 4. An automatic antenna steering system comprising a plurality of spaced apart antennas,

an amplitude modulator,

phase shift means connected to the output of said modulator,

means to combine received antenna signals additively,

means coupling the output from one of said antennas to said combining means,

means coupling the output of said phase shift means to said combiner,

an oscillator producing a fixed frequency substantially different from the frequency of the received signals,

the output of said oscillator being applied to said modulator,

phase shift control means to control the amount of phase shift produced by said phase shift means, the output of said oscillator also being connected to said phase shift controlmeans,

receiving means coupled to said combiner,

frequency demodulating means coupled to said receiver,

said phase shift control means being adapted to compare the signal received .from said oscillator and said demodulator and to control said phase shift means in accordance with the phase shift between said compared frequencies,

whereby the amount, of phase shift introduced will determine the directive patterns of the antenna array.

5. An automatic antenna steering system comprising a plurality of spaced apart antennas,

an amplitude modulator,

phase shift means connected to the output of said modulator,

means tocombine received antenna signals additively,

means coupling the output from one of said antennas to said combining means,

means coupling the output of said phase shift means to said combiner,

an oscillator producing a fixed frequency substantially different from the frequency of the received signals, the output of said oscillator being applied to said modulator,

phase shift control meansto control the amount of phase shift produced by said phase shift means, receiving means coupled to said combiner,

frequency demodulating means coupled to said receiver,

the output of said demodulator means controlling said phase shift control means.

6. A method of automatically rotating adirective beam produced from an antenna array and automatically fixing it to the direction from which an unknown signal emanates comprising the steps of receiving said signal by afirst antenna,

receiving said same signal by a second antenna,

amplitude modulating the signal received from said first antenna at a predetermined frequency and thereafter shifting the phrase of said modulated signal,

combining the phase shifted modulated signal with the signal received from said second antenna whereby said combined signal will have a frequency modulatedcomponent dependent upon said modulating signaland whereby said modulating component will have an amplitude depending upon the phase shift between the signals received atthe respective antennas,

frequency demodulating said combined signals to detect the modulating signal,

thereafter controlling the amount of phase shift applied to said received signal in accordance with the demodulated signal,

whereby said directive beam is rotated in a manner to eliminate the phase shift between received signals.

7. An automatic antenna steering system comprising a plurality of spaced apart antennas,

a frequency modulator,

phase shift means connectedztothe output of said modul-ator,

means to' combine. induced antenna signals additively,

means coupling the output from one of said antennas to said combining means,

means coupling the output of said' phase shift means to said combiner,

phase shift control means to control the amount of phase shift produced by said phase shift means, the output of saidoscillator also being connected to said phase shift control means,

receiving means coupled to said combiner,

amplitude demodulating means coupled to said receiver to: detect thecomponent of modulation produced by said oscillator,

the output of'sai d' demodulator means also being connected to said phase shift control means, said phase shift control means being adapted to compare the signal received from said oscillator and said demodulator and to control said' phase shift means, whereby the amount of phase shiftintroduced will determine the directive patterns of the antenna array.

8. The automatic antenna steering system of claim 7 in'which said phase shift control means includes a two phase servo motor having two stator windings,

and in which the said oscillator and demodulator apply their outputs to the respective stator windings. 9. A method of automatically rotating a directive beam produced from an-antenna array and automatically fixing it to the direction from which an unknown signal emanates comprising the steps of receiving said signal by a first antenna,

receiving said same signalby a second: antenna, frequency modulating the signal received from said first anten'naat a predetermined frequency and thereafter shifting the phase of said modulated signal,

combining the phase shifted modulatedsignal with the signal received from said second antenna,

amplitudedemodulating' said combined signals,

and comprising the modulating signal and the" said demodulated signal to control the amount of phase shift applied to said received signal,

whereby said directive" b'earn is rotated in a manner to eliminate thephase shift between received signals.

UNITED STATES PATENT OFFICE CE TIFIGATE 0F CG ECTIQN Patent N09 3, 140,490 July- 7 Y 1964 William Sicha'k et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 51 for "comprising read comparing Signed and sealed this 17th day of November 1964,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attcsting Officer 7 Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nov 3 140,490 Ju1y- 7 1964 William Sicha'k et al.

I It isv hereby certified that error-appears in the above numbered paterit requiring correction and that the said Letters Patentshould read as corrected below.

Column 8 line .51 for "comprising" read comparing Signed and sealed this 17th day of November 1964.,

(SEAL) Attest:

ERNEST W; SWIDER EDWARD J. BRENNER Attcsting Officer 7 Commissioner of Patents

Claims

3. A METHOD OF AUTOMATICALLY ROTATING A DIRECTIVE BEAM PRODUCED FROM AN ANTENNA ARRAY AND AUTOMATICALLY FIXING IT TO THE DIRECTION FROM WHICH AN UNKNOWN SIGNAL EMANATES COMPRISING THE STEPS OF RECEIVING SAID SIGNAL BY A FIRST ANTENNA, RECEIVING SAID SAME SIGNAL BY A SECOND ANTENNA, MODULATING THE SIGNAL RECEIVED FROM SAID FIRST ANTENNA AT A PREDETERMINED FREQUENCY BY A FIRST MODE OF MODULATION, COMBINING THE MODULATED SIGNAL WITH THE SIGNAL RECEIVED FROM SAID SECOND ANTENNA WHEREBY SAID COMBINED SIGNAL WILL HAVE A MODULATION COMPONENT DEPENDENT UPON THE MODULATING SIGNAL AND WHEREBY SAID MODULATING COMPONENT WILL HAVE A PHASE SHIFT AS COMPARED WITH THE MODULATING SIGNAL EQUAL TO THE PHASE SHIFT BETWEEN THE SIGNALS RECEIVED AT THE RESPECTIVE ANTENNAS, DEMODULATING SAID COMBINED SIGNALS BY A SECOND MODE OF MODULATION TO DETECT THE STRENGTH OF SAID MODULATING SIGNAL, AND COMPARING THE MODULATING SIGNAL AND THE SAID DEMODULATED SIGNAL AND THEREAFTER CONTROLLING THE AMOUNT OF PHASE SHIFT APPLIED TO SAID RECEIVED SIGNAL IN ACCORDANCE WITH THE COMPARED SIGNALS, WHEREBY SAID DIRECTIVE BEAM IS ROTATED IN A MANNER TO ELIMINATE THE PHASE SHIFT BETWEEN RECEIVED SIGNALS.