Adaptive antenna array and method of operating same

• US 4,173,759 A
• Filed: 11/06/1978
• Issued: 11/06/1979
• Est. Priority Date: 11/06/1978
• Status: Expired due to Term

• Current Assignee: Cubic Corporation
• Original Assignee: Cubic Corporation
• Inventors: Bakhru, Keshoolal
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US05/957,733
• Time in Patent Office: 365 Days
• Field of Search: 343/100 LE, 343/100 BL, 343/371
• US Class Current: 342/382
• CPC Class Codes: H01Q 3/2617 Array of identical elements
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming

Abstract

In the disclosed invention, electronic signals containing both information signals and interference signals in one frequency band are received from an array of N antenna elements. These signals are multiplied by the respective complex weights u_k +jv_k where k varies from 1 through N. Each of the product terms thus formed is then summed and demodulated. The demodulated sum signal is bandpass filtered to form a signal S_S which is representative of the sum of the demodulated information signals. Simultaneously, the demodulated sum signal is bandreject filtered to obtain a signal I_S +N_S which is representative of the interference signals. Utilizing signals S_S and I_S +N_S, the complex weights are modified such that the time rate of change of u_k and v_k respectively is proportional to the time rate of change of T_e with respect to u_k and v_k where T_e is the ratio of power in signals S_S and I_S +N_S.

Claims

1. A method of maximizing the ratio of information signal power to interference plus noise power in an array of N antenna elements including the steps of:

generating at each of said antenna elements composite electrical signals R_K =S_KA +I_KA +N_KA where 1≦

K≦

N, S_KA is a modulated information signal in a first frequency band, I_KA is at least one interference signal in said first frequency band, and N_KA is noise produced in said antenna elements;

multiplying each of said signals R_K by respective complex weights u_k +jv_k to form product terms;

summing all of said product terms to thereby form a signal R_S ;

demodulating said R_S signal;

bandpass filtering said demodulated R_S signal to obtain a signal S_S of a second bandwidth that is substantially less than said first bandwidth and which is representative of the sum of the demodulated S_KA signals;

bandreject filtering said demodulated R_S signal to obtain a signal I_S +N_S lying outside of said second bandwidth which is representative of the sum of said interference signals I_KA and said noise N_KA ;

determining terms P_se and P_I which respectively indicate the power in said signals S_S and I_S +N_S and;

modifying said complex weights u_k +jv_k such that the time rate of change u_k is proportional to the rate of change of T_e with respect to u_k, and such that the time rate of change of v_k is proportional to the rate of change T_e with respect to v_k, where T_e is representative of the ratio of P_se to P_I.

2. A method according to claim 1 and further including the steps of:

changing the phase of each of said R_K signals by 90°

to obtain respective signals R_KC ;

demodulating said R_K and R_KC signals;

bandpass filtering said demodulated R_K and R_KC signals to obtain signals S_K and S_KC respectively of said second bandwidth and which are representative of the individually demodulated S_KA signals;

bandreject filtering said demodulated R_K and R_KC signals to obtain signals I_K +N_K and I_KC +N_KC respectively lying outside said second bandwidth and which are representative of said individual interference signals I_KA and said noise N_KA ;

performing time average correlations on signals S_S and S_K ;

S_S and S_KC ;

I_S +N_S and I_N +N_K ;

I_S +N_S and I_KC +N_KC ; and

using said time average correlations to modify said complex weights u_k +jv_k.

3. A method according to claim 2 wherein said complex weights are modified according to the expressions ##EQU1## where the overbar indicates time average correlation of the signals below, and where C and C₂ are predetermined loop gains.

4. A method according to claim 2 wherein said complex weights are modified according to the expressions ##EQU2## where the overbar indicates time average correlation of the signals below, and where C₁ and C₂ are predetermined loop gains.

5. A method according to claim 2 wherein said steps for forming terms R_K, R_KC, S_K, S_KC, I_K +N_K, and I_KC +N_KC are performed sequentially for various values of K, 1≦

K≦

N.

6. A method according to claim 2 wherein said steps of forming terms R_K, R_KC, S_K, I_K +N_K, and I_KC +N_KC are performed in parallel where 1≦

K≦

N.

7. A method according to claim 4 wherein said predetermined loop gains are constant.

8. A method according to claim 4 wherein said predetermined loop gains are time variable.

9. An adaptive antenna array for maximizing the ratio of information signal power to interference plus noise power comprised of:

a plurality of N antenna elements for generating composite electrical signals R_K =S_KA +I_KA +N_KA where 1≦

K≦

N, S_KA is a modulated information signal in a first frequency band, I_KA is at least one interference signal in said first frequency band, and N_KA is noise produced in said antenna elements;

multiplication means for multiplying each of said signals R_K by respective complex weights u_k +jv_k to form product terms;

adder means for summing all of said product terms to thereby form a signal R_S ;

demodulation means for demodulating said R_S signal;

bandpass filter means for filtering said demodulated R_S signal to obtain a signal S_S of a second bandwidth that is substantially less than said first bandwidth and which is representative of the sum of the demodulated S_KA signals;

bandreject filter means for filtering said demodulated R_S signal to obtain a signal I_S +N_S lying outside of said second bandwidth which is representative of the sum of said interference signal I_KA and said noise N_KA ;

means for generating signals P_se and P_I which respectively indicate the power in said signals S_S and I_S +N_S and;

means for modifying said complex weights u_k +jv_k such that the time rate of change u_k is proportional to the rate of change of T_e with respect to u_k, and such that the time rate of change of v_k is proportional to the rate of change T_e with respect to v_k, where T_e is representative of the ratio of P_se to P_I.

10. An adaptive antenna array according to claim 9 and further including,

means for changing the phase of each of said R_K signals by 90°

to obtain respective R_KC signals;

means for demodulating said R_K and R_KC signals;

means for bandpass filtering said demodulated R_K and R_KC signals to obtain signals S_K and S_KC respectively of said second bandwidth and which are representative of the individually demodulated S_KA signals;

means for bandreject filtering said demodulated R_K and R_KC signals to obtain signals I_K +N_K and I_KC +N_KC respectively lying outside said second bandwidth and which are representative of said individual interference signals I_KA and said noise N_KA ;

means for performing time average correlations on signals S_S and S_K ;

S_S and S_KC ;

I_S +N_S and I_N +N_K ;

I_S +N_S and I_KC +N_KC ; and

means for combining said time average correlations to modify said complex weights u_k +jv_k.

11. An adaptive antenna array according to claim 10 wherein said means for combining including means for modifying said complex weights according to the expressions ##EQU3## where the overbar indicates time average correlation of the signals below, and where C, and C₂ are loop gains.

12. An adaptive antenna array according to claim 10 wherein said means for combining includes means for modifying said complex weights according to the expressions ##EQU4## where the overbar indicates time average correlation of the signals below, and where C₁ and C₂ are loop gains.

13. An adaptive antenna array according to claim 10 and further including switching means between said antenna elements and a single set of said means for demodulating means for bandpass filtering means for bandreject filtering, and means for time average correlating to enable terms R_K, R_KC, S_K, S_KC, I_K +N_K and I_KC +N_KC to be sequentially formed for various values of K, 1≦

K≦

N.