Phase conjugation method and apparatus for an active retrodirective antenna array

• US 4,148,031 A
• Filed: 03/16/1977
• Issued: 04/03/1979
• Est. Priority Date: 03/16/1977
• Status: Expired due to Term

• Current Assignee: James C. Fletcher, Ralph C. Chernoff, Robert C. Tausworthe
• Original Assignee: James C. Fletcher, Ralph C. Chernoff, Robert C. Tausworthe
• Inventors: Chernoff, Ralph C., Fletcher, James C., Tausworthe, Robert C.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US05/777,983
• Time in Patent Office: 748 Days
• Field of Search: 343/100 SA, 343/754, 343/854, 343/100 TD
• US Class Current: 342/370
• CPC Class Codes: H01Q 3/2647 Retrodirective arrays

Abstract

An active retrodirective antenna array wherein a reference array element is used to generate a phase reference which is replicated at succeeding elements of the array. Each element of the array is associated with a phase regeneration circuit and the phase conjugation circuitry of an adjacent element. In one implementation, the phase reference circuit operates on the input signal at the reference element, a voltage controlled oscillator (VCO) output signal and the input pilot signal at the next array element received from a transmission line. By proper filtering and mixing, a phase component may be produced to which the VCO may be locked to produce the phase conjugate of the pilot signal at the next array element plus a transmission line delay. The same phase conjugation process occurs at the next element where the proper phase reference is regenerated by mixing samples of the input pilot and transmitted signal. In another implementation, particularly suited for large arrays in space, two different input pilot frequencies are employed. Their difference is the phase reference of the system, and a local oscillator is used in obtaining this difference, which is in the IF range. The two pilot frequencies are selected in accordance with particular criteria to insure proper phase addition and elimination of local oscillator components. Appropriate mixing and filtering is performed to achieve phase conjugation and phase reference replication.

Claims

1. In an active retrodirective antenna array for directing a transmitted beam in the direction of an incident pilot signal, the combination comprising:

as least first and second antenna element means;

a first transmission line means exhibiting transmission line delay interconnecting said first and second antenna element means;

said first antenna element means including means receiving a transmitted signal from said second antenna element means across said transmission line means and operative on said transmitted signal and the incident pilot signal at said first antenna element means for generating a phase reference and the phase conjugate of the pilot signal inputted to said second antenna element means plus a transmission line delay.

2. The antenna array of claim 1 further including:

a third antenna element means;

a second transmission line means connecting said second antenna element means to said third antenna element means and further including means in said second antenna element means for regenerating said phase reference and for producing the phase conjugate of the pilot signal inputted to said third antenna element means plus a transmission line delay.

3. The antenna array of claim 2 wherein said means for generating a phase reference and the phase conjugate comprises:

a voltage-controlled oscillator; and

means for operating on components of the input pilot signal at said second antenna element means, the input pilot signal to said first antenna element means, and the output of said voltage-controlled oscillator to produce a control signal such that when said voltage-controlled oscillator is in lock with said control signal, said voltage-controlled oscillator'"'"'s output is the phase conjugate of the input pilot signal at said second element means plus a transmission line delay.

4. The antenna array of claim 3 wherein said means for operating includes:

means for multiplying the phase of the input pilot signal received by said first element, thereby producing a multiplied signal; and

means for mixing and filtering the output of said voltage-controlled oscillator, the transmitted signal, and the multiplied signal to produce said control signal.

5. The antenna array of claim 4 wherein said mixing and filtering means comprises:

first mixer means for mixing said voltage-controlled oscillator output and said transmitted signal;

means for selecting the upper sideband phase component from the output of said first mixer means;

second mixer means for mixing said upper sideband phase component and said multiplied signal; and

means for selecting the upper sideband component of said second mixer means for supply to said voltage-controlled oscillator.

6. The antenna array of claim 4 wherein the input pilot signal phase received by said first element means is multiplied by twice a transponding ratio and wherein said transmitted signal is multiplied by the transponding ratio before said mixing and filtering.

7. The antenna array of claim 6 wherein said first transmission line means returns the output of said voltage-controlled oscillator to said second element means, thereby producing an output signal and further including means for amplifying the said output signal.

8. The antenna array of claim 7 wherein said output signal and transmitted signal pass between a first multiplexing means interfacing with said first transmission line means, wherein said output signal is fed from said second multiplexing means to said means for amplifying, said means for amplifying then being connected to output to said first multiplexing means and wherein said output and transmitted signal are tapped near said first multiplexing means for supplying to said means for regenerating said phase reference and for producing the phase conjugate.

9. The antenna array of claim 3 wherein said means for regenerating said phase reference and producing the phase conjugate includes:

means for sampling the pilot signal at said second element means.

means for sampling the transmitted signal at said second element means; and

means for mixing the samples of said pilot and transmitted signals to regenerate said reference.

10. The antenna array of claim 1 wherein said input pilot signal at each array element includes first and second phase components having first and second frequencies, respectively, and wherein said means for generating a phase reference and the phase conjugate comprises:

means for producing the difference of said first and second phase components of the pilot signal at said first antenna element means; and

means for mixing said difference with phase components derived at said second antenna element means and transmitted across said first transmission line means to produce the phase conjugate of the input pilot signal received by said second element.

11. The antenna array of claim 10 wherein said difference producing means includes a local oscillator producing a local oscillator frequency, and wherein said local oscillator frequency is between but not exactly half-way between said first and second frequencies.

12. The antenna array of claim 11 wherein the difference of said first and second frequencies is in the IF range.

13. The antenna array of claim 11 wherein said difference producing means further includes:

means for mixing the local oscillator phase component and said first and second phase components;

means for filtering out of said mixing means a first receiver phase component equal to said first component minus said local oscillator phase component, and a second receiver component equal to said local oscillator phase component minus said second phase component; and

means for producing said difference from said first and second receiver component frequencies.

14. The antenna array of claim 1 wherein each of said antenna element means receives a pilot signal containing first and second phase components having first and second frequencies respectively and has circuitry associated therewith comprising:

receiver means for mixing a local oscillator phase component with the first and second phase components received by the respective antenna element to produce first and second receiver phase components.

15. The antenna array of claim 14 wherein said first antenna element means has circuitry associated therewith comprising:

means for producing the difference of the first and second phase components at said first antenna element means; and

first phase conjugation means for producing the phase conjugate of the input signal received by a second of said antenna element means from said difference and the first and second receiver phase components transmitted from said second antenna element means.

16. The antenna array of claim 15 wherein said second antenna element means has circuitry associated therewith comprising:

means for regenerating said difference from the first and second receiver phase components at said second element means and the phase conjugate of the input pilot signal at said second element means; and

second phase conjugation means for producing the phase conjugate of the input pilot signal received by a third of said antenna element means from the regenerated difference supplied by said regenerating means and from the first and second receiver phase components received from said third element means.

17. The antenna array of claim 16 wherein said difference producing means comprises:

means for mixing said first and second phase components and filtering out said difference.

18. The antenna array of claim 16 wherein said first phase conjugation means comprises:

means for mixing said difference with said first and second phase components and filtering out third and fourth phase components; and

means for mixing said third and fourth phase components and filtering out the phase conjugate of the input pilot signal at said second element means.

19. The antenna array of claim 16 wherein said second phase conjugation means comprises:

means for mixing said difference with the first and second phase components produced by the receiver means at said third element means and filtering out third and fourth components; and

means for mixing said third and fourth components and filtering out the phase conjugate of the input pilot signal received by said third element means.

20. The antenna array of claim 16 wherein said regenerating means comprises:

means for dividing the phase conjugate signal received from said first phase conjugating means to produce a divided signal;

means for mixing said divided signal with the receiver phase components produced by the receiving means of said second element means and filtering out third and fourth phase components;

means for mixing said third and fourth phase components; and

means for dividing the output of said means for mixing said third and fourth phase components to produce said difference.

21. The antenna array of claim 16 wherein said regenerating means comprises:

means for mixing said divided signal with the first receiver phase component produced by the receiver means at said second element means and filtering out a third phase component;

means for mixing said third phase component with the second receiver phase component produced by the receiver means at said second element means and filtering out a fourth phase component; and

means for dividing said fourth phase component to produce said difference.

22. A method of phasing an active retrodirective antenna element array comprising the steps of:

generating a phase reference from the pilot signal received at a first of said elements;

transmitting the pilot signal received by a second of said elements to said first element;

producing the phase conjugate of the pilot signal received by said second element at said first element from said phase reference and the pilot signal transmitted from said second element;

transmitting said phase conjugate back to said second element;

regenerating said phase reference at said second element from the pilot and transmitted signals at said second element; and

producing the phase conjugate for the third element at said second element from the regenerated phase reference and the input pilot signal transmitted from said third element.

23. In an active retrodirective antenna array for directing a transmitted beam in the direction of an incident pilot signal, the combination comprising:

a plurality of antenna elements;

means for generating a phase reference and the phase conjugate of the pilot signal inputted to a second of said antenna elements, said means including;

a voltage-controlled oscillator; and

means for operating on components of the input pilot signal at said second antenna element, the input pilot signal to said first antenna element, and the output of said voltage-controlled oscillator to produce a control signal such that when said voltage-controlled oscillator is in lock with said control signal, said voltage-controlled oscillator'"'"'s output includes the phase conjugate of the input pilot signal at said second element.

24. In an active retrodirective antenna array for directing a transmitted beam in the direction of an incident pilot signal containing first and second phase components and having first and second frequencies respectively, the combination comprising:

a plurality of antenna elements; and

means associated with a first of said antenna elements for generating a phase reference and the phase conjugate of the pilot signal inputted to a second of said antenna elements, said means including receiver means for mixing a local oscillator phase component with the first and second phase components received by the respective antenna elements to produce first and second receiver phase components.