RF signal direction finding apparatus

• US 4,978,963 A
• Filed: 03/26/1990
• Issued: 12/18/1990
• Est. Priority Date: 10/31/1988
• Status: Expired due to Fees

• Current Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Thorpe, J. Carlton
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US07/498,469
• Time in Patent Office: 267 Days
• Field of Search: 342/375, 342/433, 342/435, 342/442
• US Class Current: 342/433
• 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

Angle of arrival of a pulsed RF signal, such as that emitted by a radar transmitter, is determined by use of a detection circuit that contains a single RF receiver. The RF signal direction of arrival determining system contains a switching means to automatically alternately switch the outputs from two physically spaced receiving antennas to the input of the RF tuner. In turn the tuner'"'"'s output is coupled to a power divider. The output of this power divider is branched, one output being coupled through a first IF amplifier to one of the two inputs of a phase detector and the second output being coupled through a second circuit, containing a delay line and an IF amplifier serially arranged, to the second input of the phase detector. The phase detector displays the phase difference between the two signals.

Claims

1. An RF direction finding system for determining angle of arrival of RF pulse signals, said pulse signals being within a predetermined range of pulse durations and within a predetermined range of pulse repetition rates, comprising:

at least two physically spaced receiving antennas;

RF tuner means for converting received RF signals applied at an input to an intermediate frequency signal at an output;

antenna switching means for alternately periodically coupling each of said antenna means to said tuner means input for essentially equal predetermined dwell intervals to pass the RF signal in the phase received at the respective antennas to said tuner;

said antenna switching means having an output coupled to said tuner means input and a pair of inputs connected to respective ones of said antennas;

power divider means;

said power divider means containing an input and two outputs;

said power divider means input being connected to the output of said tuner means for dividing the inputted intermediate frequency signal between two power divider means outputs;

phase detector means;

first branch circuit means for coupling one output of said power divider to a first input of said phase detector means, said first branch circuit means including IF amplifier means;

second branch circuit means, including signal delay means and IF amplifier means serially connected, coupled in circuit between said second output of said power divider and a second input of said phase detector;

said signal delay means for delaying the application of signals applied at an input to an output by a predetermined delay interval;

said antenna switching means being operative to switch between antennas within a predetermined switching interval, and at a predetermined switching rate;

said switching interval being substantially less than said predetermined dwell interval and substantially less than said delay interval;

said dwell interval being no greater than one half of said pulse width or duration;

whereby IF signals representative of RF signal received at the first antenna and of the same signal as received at the second antenna overlaps in time at the input of said phase detector means.

3. The invention as defined in claim 1 wherein said predetermined delay interval of said signal delay means is equal to the sum of the dwell interval of said switching means and one half of the switching time of said switching means.

2. The method of determining the angle of arrival of an RF signal propagating in space including the steps of:

sampling the signal as received at each of two spaced locations to provide a serial signal stream containing alternate samples of said RF signal displaced in time;

branching said stream into two channels, a first channel and a second channel;

delaying the passage of said RF signal stream through said first channel to delay arrival of the signals for a predetermined interval; and

comparing the outputs of the two channels and determining the phase difference between the signals from the two channels.

4. An RF direction finding system for determining angle of arrival of RF pulse signals, said pulse signals being within a predetermined range of pulse durations and within a predetermined range of pulse repetition rates, said system containing at least two physically spaced receiving antennas and RF signal processing means for processing RF signals, comprising in combination:

switching means for periodically coupling each of said antennas to said RF signal processing means for alternately consecutively applying a signal representative of a RF pulse received at each said antenna concurrently to each of a first and second signal transmission channels;

said switching means maintaining each antenna coupled to said processing means for a predetermined dwell interval and having a transition interval, substantially smaller than said dwell interval, in which said switching means couples neither antenna to said processing means;

said first transmission channel including delay means for delaying an inputted signal for a predetermined interval;

said second transmission channel being substantially identical to said first transmission channel in all respects excluding said delay means;

whereby the signal outputted from said second channel is displaced in time from the same signal outputted from said first channel;

phase measuring means coupled to the outputs of both channels for displaying the difference in phase between said channel outputs.

5. The invention as defined in claim 4 wherein said predetermined delay time interval equals the sum of one half of the duration of the RF pulse and the transition switching time of said switching means.

6. An RF direction finding system for determining the angle of arrival of an RF pulse signal, said direction finding system containing at least two antennas for receiving propagating RF pulse signal with said antennas being spaced physically from one another, whereby said angle of arrival is represented by difference in electrical phase in the RF signal as received at the different antennas, and RF signal processing means for processing RF signals;

the improvement wherein said RF signal processing means comprises;

first means for periodically alternately coupling to each of said antennas to define a composite signal representative of an RF pulse received at each said antenna and for applying said composite signal concurrently to each of a first and second signal transmission channel;

said first transmission channel including delay means for delaying an inputted signal for a predetermined interval;

whereby the signal outputted from said second signal transmission channel is displaced in time from the same signal outputted from said first signal transmission channel; and

phase measuring means coupled to the outputs of said first and second signal transmission channels for determining the difference in phase between signals outputted from said first and second signal transmission channels.

7. The invention as defined in claim 6 wherein said first means includes switching means for coupling to said antennas for a predetermined dwell interval, and wherein said switching means has a transition interval between said dwell intervals in which said switching means couples neither antenna, said transition interval being substantially smaller than said dwell intervals.

8. The invention as defined in claim 7 wherein said RF pulse signal is within a predetermined range of pulse durations;

wherein said dwell interval is less than said pulse duration; and

wherein said predetermined interval provided by said delay means equals the sum of one half of the duration of the RF pulse and the transition switching time of said switching means.

9. The invention as defined in claim 8 wherein said switching means comprises:

RF switching means having two inputs and an output;

RF tuner means for deriving an IF signal from inputted RF signals;

said output of said switching means being coupled to said RF tuner means for supplying RF signals thereto;

power divider means having an input and two outputs for dividing signals applied at an input to said two outputs;

said input of said power divider means being coupled to said RF tuner means and said two outputs of said power divider means being coupled to said first and second signal transmission channels, respectively.

10. The invention as defined in claim 9 wherein said first transmission channel includes IF amplifier means;

and wherein said second transmission channel includes IF amplifier means.

11. The invention as defined in claim 10 wherein said phase measuring means comprises further:

phase detector means, said phase detector means being coupled to said outputs of said first and second signal transmission channels and providing two outputs; and

oscilloscope means coupled to said phase detector means for displaying the relative electrical phase indicium outputted from said phase detector means.

12. The invention as defined in claim 11 wherein said second transmission channel is substantially identical to said first transmission channel in all respects, exclusive of said delay means.

13. The invention as defined in claim 6 wherein said second transmission channel is substantially identical to said first transmission channel in all respects, exclusive of said delay means.

14. The invention as defined in claim 6 wherein said first means comprises:

RF switching means having two inputs and an output;

RF tuner means for deriving an signal from inputted RF signals;

said output of said switching means being coupled to said RF tuner means for supplying RF signals thereto;

power divider means having an input and two outputs for dividing signals applied at an input to said two outputs;

said input of said power divider means being coupled to said RF tuner means and said two outputs of said power divider means being coupled to said first and second signal transmission channels, respectively.

15. The invention as defined in claim 14 wherein said phase measuring means comprises further:

phase detector means, said phase detector means being coupled to said outputs of said first and second signal transmission channels and providing two outputs; and

oscilloscope means coupled to said phase detector means for displaying the relative electrical phase indicium outputted from said phase detector means.

16. The invention as defined in claim 6 wherein said RF pulse signal is within a predetermined range of pulse durations;

wherein said dwell interval is no greater than one half of said pulse duration; and

wherein said predetermined interval provided by said delay means equals the sum of one half of the duration of the RF pulse and the transition switching time of said switching means.

17. In an RF system containing RF transmitter means for transmitting RF pulses and RF receiver means for receiving RF pulses and direction finding means included with said receiver means for determining the angle of arrival at said receiver means of an RF pulse signal from said RF transmitter means, said RF receiver means containing at least two antennas for receiving propagating RF with said receiving antennas being spaced physically apart from one another, and RF signal processing means for processing RF signals received by said RF receiver means, the improvement in which said RF signal processing means includes in combination:

first means for periodically alternately coupling to each of said antennas in circuit to define a composite signal representative of RF pulses received at each said antenna and for applying said composite signal to each of a first and second signal transmission channels;

said first transmission channel including delay means for delaying an inputted signal for a predetermined interval;

whereby the signal outputted from said second signal transmission channel is displaced in time from the same signal outputted from said first signal transmission channel; and

phase measuring means coupled to the outputs of said first and second signal transmission channels for determining the difference in phase between signals outputted from said first and second signal transmission channels.

18. The invention as defined in claim 17 wherein said first means includes switching means for coupling to each antenna for a predetermined dwell interval;

and wherein said switching means has a transition interval between said dwell intervals in which said switching means couples to neither antenna, said transition interval being substantially smaller than said dwell intervals.

19. The invention as defined in claim 18 wherein said RF pulse signal is within a predetermined range of pulse durations;

wherein said dwell interval is less than said pulse duration; and

wherein said predetermined interval provided by said delay means equals the sum of one half of the duration of the RF pulse and the transition switching time of said switching means.

20. The invention as defined in claim 19 wherein said second transmission channel is substantially identical to said first transmission channel in all respects, exclusive of said delay means.

21. The invention as defined in claim 19 wherein said first means comprises:

RF switching means having two inputs and an output;

RF tuner means for deriving an IF signal from inputted RF signals;

said output of said switching means being coupled to said RF tuner means for supplying RF signals thereto;

power divider means having an input and two outputs for dividing signals applied at an input to said two outputs;

said input of said power divider means being coupled to said RF tuner means and said two outputs of said power divider means being coupled to said first and second signal transmission channels, respectively.

22. The invention as defined in claim 18 wherein said RF pulse signal is within a predetermined range of pulse durations;

wherein said dwell interval is no larger than one half of said pulse duration; and

wherein said predetermined interval provided by said delay means equals the sum of one half of the duration of the RF pulse and the transition switching time of said switching means.

23. Apparatus for determining the angle of arrival of an RF signal emitted by a remote transmitter, comprising:

receiving means responsive to reception of said RF signal at two spaced locations for forming a composite signal, containing a signal sample representative of the RF signal received at one location alternating seriatum with a signal sample representative of the RF signal from the other location;

signal transmission means responsive to said composite signal for outputting said composite signal at first and second outputs;

said signal transmission means including delay means for delaying said composite signal output at said first output to cause a signal sample received at said one location and contained within said composite signal in said first channel to overlap in time with a signal sample received at said other location and contained within said composite signal in said second channel; and

phase indicating means responsive said outputs from said signal transmission means for providing a representation of electrical phase difference between aid channel outputs;

whereby said angle of arrival of said RF signal is obtained.