Direction finding techniques employing electronic phase modulation

• US 3,872,477 A
• Filed: 07/19/1972
• Issued: 03/18/1975
• Est. Priority Date: 07/19/1972
• Status: Expired due to Term

• Current Assignee: John P. King
• Original Assignee: John P. King
• Inventors: King, John P.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Blum, T. M.
• Application Number:
  US05/273,151
• Time in Patent Office: 972 Days
• Field of Search: 343/113R,120
• US Class Current: 342/433
• CPC Class Codes: G01S 3/14 Systems for determining direction or deviation from predetermined direction aerial arrangements for changing or varying the orientation or the shape of the directional pattern H01Q3/00; combinations of different interacting aerial units for giving a desired directional characteristic H01Q21/29; aerials or aerial systems providing at least two radiation patterns H01Q25/00
• CPC Class Codes: G01S 3/48 the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured

Abstract

Radio frequency signals received by two antennas positioned a fixed distance apart are combined into a composite electrical signal that is modulated according to the phase difference between the signals developed at each of the two antennas. A technique of forming a composite signal that is phase modulated by switching between the two antenna signals at an audio rate is disclosed. Alternatively, a phase modulated composite signal is formed by balance modulating at a constant frequency the signal from one antenna, shifting its phase, and adding the modulated signal to the signal from the other antenna. A radio receiver demodulates the composite signal and forms an audio tone whose magnitude and sense is proportional to the bearing angle of a particular radio signal of interest with respect to the two antennas.

Claims

1. A method of determining a bearing signal of an electromagnetic energy wavefront relative to two receiving antennas, comprising the steps of:

modulating an electrical signal from one of said antennas with a modulating signal of constant frequency in order to generate a pair of sidebands with carrier suppressed, adding the modulated signal to an electrical signal from the other of said antennas to form a composite signal, and generating an error signal proportional to the degree of phase or amplitude modulation of said composite signal and thereby also proportional to the bearing angle of said electromagnetic energy wavefront, said error signal generation including the steps of;

applying the composite signal to an antenna input of a frequency modulation responsive radio receiver, thereby detecting the degree of phase modulation of said composite signal, and utilizing an audio output of said receiver for indicating the bearing angle.

2. A method of determining a bearing signal of an electromagnetic energy wavefront relative to two receiving antennas, comprising the steps of:

modulating an electrical signal from one of said antennas with a modulating signal of constant frequency in order to generate a pair of sidebands with carrier suppressed, adding the modulated signal to an electrical signal from the other of said antennas to form a composite signal, generating an error signal proportional to the degree of phase or amplitude modulation of said composite signal And thereby also proportional to the bearing angle of said electromagnetic energy wavefront, and utilizing said error signal to automatically adjust in response to the error signal relative time delays in the paths of the electrical signals from the two antennas which minimizes siad error signal and thus which minimized the degree of phase modulation of the composite signal, whereby the difference in time delay interposed in the paths of the electrical signals from the two antennas is equal to a desired difference in time of arrival of the electromagnetic energy wavefront at said two antennas.

3. A system of developing a signal proportional to the phase difference between first and second electrical signals developed by two antennas that are positioned a fixed distance apart, comprising:

means receiving said first signal for amplifying said first signal, a constant frequency oscillator within the audio range, modulating means receiving said second signal and an output of said constant frequency oscillator for developing a double sideband suppressed carrier signal at an output, means for adding the amplified first signal and the modulating means output signal to form a composite signal that may be applied to a radio receiver antenna terminal, and means adapted to receive an audio output of the radio receiver for developing an error signal whose magnitude is proportional to the phase difference between said first and second electrical signals.

4. A system according to claim 3 wherein a phase shifting network is disposed between said modulating means and said adding means.

5. A system according to claim 3 wherein said constant frequency oscillator is a squarewave oscillator having a frequency within the range of about 300-2500 Hz.

6. A system according to claim 3 which includes a F.M. radio receiver having antenna terminals receiving the composite signal and an audio output connected to said error signal developing means, whereby the degree of phase modulation of the composite signal is detected and presented at the audio output of said receiver.

7. A system according to claim 3 which includes an A.M. radio receiver having antenna terminals receiving said composite signal and an audio output connected to said error signal developing means, whereby the degree of amplitude modulation of said composite signal is detected by the receiver and presented at its audio output.

8. A system according to claim 3 which additionally comprises a beam forming network connected to receive signals from the two antennas at its input and to develop said first and second signals at its output, said first and second signals being different combinations of the signals from both of the two antennas.

9. A system according to claim 6 wherein said modulating means output signal is applied to the adding means without any significant phase shifting of said modulating means output signal.

10. A system according to claim 7 which additionally comprises phase shifting means disposed between said modulating means output and said adding means for shifting the modulating means output signal substantially ninety degrees before being added to the amplified first signal.

11. A system according to claim 8 wherein said beam forming network is a hybrid pi network.

12. A method of determining a bearing signal of an electromagnetic energy wavefront relative to two receiving antennas, comprising the steps of:

modulating an electrical signal from one of said antennas with a modulating signal of constant frequency in order to generate a pair of sidebands with carrier suppressed, adding the modulated signal to an electrical signal from the other of said antennas to form a composite signal, and generating an error signal proportional to the degree of phase or amplitude modulation of said composite signal and thereby also proportional to the bearing angle of said electromagnetic energy wavefront, said error signal generaTion including the steps of;

applying the composite signal of an antenna input of an amplitude modulation responsive radio receiver, thereby detecting the degree of amplitude modulation of said composite signal, and utilizing an audio output of said receiver for indicating the bearing angle.

13. A system for determining a bearing angle of an electromagnetic wavefront relative to two antennas, comprising:

means including a beam forming network for receiving signals from said two antennas and for producing first and second output signals that are different combinations of the signals from both of said two antennas, an oscillator, a modulating means receiving said first network output signal and an output of said oscillator for developing a double sideband suppressed carrier signal at an output, means receiving said modulating means output and said second network output signal for summing into a composite signal, whereby said composite signal is both phase and amplitude modulated in degrees proportional to said wavefront bearing angle to be determined.

14. A system according to claim 13 wherein said beam forming network includes a hybrid pi network.

15. A system for determining a bearing angle of an electromagnetic wavefront relative to an observer, comprising:

first and second antennas, an audio frequency oscillator, modulating means receiving a signal from one of said antennas and an output of said audio frequency oscillator for developing a double sideband suppressed carrier signal at an output thereof, means receiving the modulating means output and a signal derived from the other of said antennas for summing the received signals together to form a composite signal, whereby said composite signal is both phase and amplitude modulated to a degree proportional to said wavefront bearing angle to be determined, an amplitude modulation responsive receiver having an antenna terminal connected to receive said composite signal, whereby an audio output of said receiver contains a signal proportional to the bearing angle of interest, and a phase shifting network disposed between said modulating means output and said summing means for shifting the phase of said modulating means output signal substantially ninety degrees before it is applied to said summing means.

16. A system for determining a bearing angle of an electromagnetic wavefront relative to an observer, comprising:

first and second antennas, an audio frequency oscillator, modulating means receiving a signal from one of said antennas and an output of said audio frequency oscillator for developing a double sideband suppressed carrier signal at an output thereof, means receiving the modulating means output and a signal derived from the other of said antennas for summing the received signals together to form a composite signal, whereby said composite signal is both phase and amplitude modulated to a degree proportional to said wavefront bearing angle to be determined, and a frequency modulation responsive receiver with an antenna terminal connected to receive said composite signal, whereby an audio output of said receiver contains a signal proportional to the bearing angle of interest.

17. The system according to claim 16 wherein there is substantially zero relative phase shift of the modulating means output signal before it is applied to said summing means.

18. A system for determining a bearing angle of an electromagnetic wavefront relative to an observer, comprising:

first and second antennas, an audio frequency oscillator, modulating means receiving a signal from one of said antennas and an output of said audio frequency oscillator for developing a double sideband suppressed carrier signal at an output thereof, means receiving the modulating means output and a signal derived from the other of said antennas for summing the received signals together to form a composite signal, whereby said composIte signal is both phase and amplitude modulated to a degree proportional to said wavefront bearing angle to be determined, a radio receiver having an antenna terminal that is connected to receive said composite signal, and a demodulator connected to an audio output of said receiver, said demodulator being driven from said audio frequency oscillator, whereby said demodulator forms a direct current output level proportional to the wavefront bearing angle of interest.

19. The system according to claim 18 which additionally comprises:

means in the path of said antenna signals for adjusting the relative phase therebetween in response to an input signal, and means receiving the direct current output error signal of said demodulating means for driving said relative phase control means in a manner to minimize said error signal.

20. A system for determining a bearing angle of an electromagnetic energy wavefront relative to an observer, comprising:

first and second antennas positioned a fixed distance apart, said antennas being responsive to said electromagnetic radiation to form electrical signals proportional thereto at their outputs, a beam forming network receiving the signals from said first and second antennas, said beam forming network being characterized by having first and second output signals that are different combinations of the signals from both of said first and second antennas, a modulator circuit receiving directly said first network output signal, said modulator characterized by developing at an output thereof a double sideband suppressed carrier signal, means receiving said modulator output without any significant phase shift and receiving said second network output signal for summing into a composite signal, and means receiving said composite signal for generating a signal proportional in level to the amount of phase modulation present in said composite signal, whereby said signal level is proportional to the bearing angle of an electromagnetic wavefront relative to said first and second antennas.

21. The system according to claim 20 where said phase modulation detector includes an FM receiver with its antenna terminal connected to receive said composite signal, thereby generating at an audio output thereof said signal level proportional to the bearing angle, said system additionally comprising means receiving the FM receiver audio output for indicating the bearing angle of said electromagnetic energy wavefront.

22. The system according to claim 21 wherein said modulator circuit includes an audio oscillator connected to modulate said first network output signal and wherein said bearing angle indicating means includes a demodulator connected to receive the audio output of said FM receiver, said demodulator being driven from said audio oscillator, whereby said demodulator forms a direct current output level proportional to the wavefront bearing angle of interest.

23. The system according to claim 20 which additionally comprises an amplifier connected to receive said second network output signal for forming an amplified version thereof, said amplified version being applied to said summing means.