Tuning amplitude slope matched filter architecture

• US 20100136925A1
• Filed: 12/03/2008
• Published: 06/03/2010
• Est. Priority Date: 12/03/2008
• Status: Active Grant

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: Lackey, Raymond J.
• Granted Patent: US 8,032,103 B2
• Time in Patent Office: Days
• US Class Current: 455/77
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H

Abstract

A tuning control system and associated method is provided for continuously and automatically tuning a lobed amplitude slope matching filter (ASMF) to a band center of an interfering signal to provide improved rejection of an interfering signal coupled from a transmission antenna into a local receive antenna in the presence of local multi-path, thereby Providing improved adaptive control loop performance. The tuning control system is provided as an element of an adaptive control loop.

Claims

1. A method for continuously and automatically frequency tuning a lobed amplitude slope matching filter (ASMF) to an inserted signal to allow tracking of the inserted signal to match a dynamically changing amplitude slope of a second signal for improved interference cancellation system performance, the method comprising:

a) forming a broadband RF lobed filter having a single quiescent null within a frequency band of interest;

b) dynamically adjusting a delay time (T) for tuning the single quiescent null of the formed broadband RF lobed filter to effectively block an interfering signal to be tracked;

c) forming a more narrowband RF lobed filter;

d) skewing the narrowband RF lobed filter to implement a corrective amplitude slope of the inserted signal, thereby improving the performance in the improved interference cancellation system; and

e) repeating steps (a)-(d).

2. The method of claim 1, wherein said step (c) of forming a more narrowband RF lobed filter is formed in dependence upon the tuning of the broadband RF lobed filter.

3. The method of claim 1, wherein the more narrowband RF lobed filter is orthogonal to the broadband RF lobed filter in its quiescent state.

4. The method of claim 1, wherein said step (d) of skewing the narrowband RF filter lobe is performed under the control of an external amplitude slope control signal.

5. The method of claim 1, wherein said narrowband RF lobed filter is comprised of a plurality of lobes within a single lobe of the formed broadband RF filter but orthogonal to it.

6. The method according to claim 5, wherein one of said plurality of lobes is peaked on the inserted signal to be tracked.

7. The method according to claim 5, wherein said one of said plurality of lobes peaked on the inserted signal to be tracked is a quiescent lobe of an amplitude sloped matching filter (ASMF) function.

8. The method of claim 6, wherein said one of said plurality of lobes peaked on the interfering signal to be tracked is centered at a null of the broadband RF lobed filter.

9. The method according to claim 1, wherein the step (b) of dynamically adjusting a delay time (T) for tuning the single quiescent null of the formed broadband RF lobed filter further comprises:

skewing the broadband RF filter quiescent null in a frequency direction to effectively reject the inserted signal to be tracked.

10. The method according to claim 1, wherein the broadband RF lobed filter has a null-to-null bandwidth substantially twice the desired tuning bandwidth.

11. The method according to claim 1, wherein the step (b) of dynamically adjusting a delay time is performed via a control process.

12. The method according to claim 11, wherein the control process comprises:

a) measuring an RF energy output from the broadband RF filter;

b) applying a delta increment to the delay time (T);

c) re-measuring the RF energy output from the broadband RF filter;

d) comparing the measured and the re-measured values of RF energy; and

e) determining if the applied delta increment to the delay time (T) improves the tuning as measured by an energy output from the broadband RF filter;

f) if improved, updating the delay time (T) by adding a positive delta increment as T=T+Δ

T; and

g) if unimproved, updating the delta delay time (Δ

T) by changing sign of delta delay time increment as Δ

T=−

Δ

T.

13. The method of claim 1, wherein increasing a control voltage causes the delay T to be increased resulting in a narrowing of the filter lobes.

14. The method of claim 13, wherein narrowing the filter lobes results in a downward frequency shift of the individual lobes and nulls of the more narrowband RF lobed filter.

15. The method of claim 1, wherein decreasing a control voltage causes the delay T to be decreased resulting in a widening of the filter lobes of the more narrowband RF lobed filter.

16. The method of claim 15, wherein widening the filter lobes results in an upward frequency shift of the individual lobes and nulls of the lobed filters.

17. An interference cancellation system, comprising:

a) an adaptively tuned sloped control (ATSC) module (200) for providing a tuning procedure directed to an ASMF control function to the band of interference and for externally controlling the ASMF control function subsequent to said tuning, said adaptively tuned sloped control (ATSC) module 200 comprising;

an inline variable lobe filter structure (VLFS) (201) for providing controlled variable time delay for generating a broadband RF tuning filter formed by a delay T and a slope control filter lobe formed by a first delay (T) (205) and a second delay (2nT) (208) yield a total time delay of (2n+1)T centered in the null of the tuning filter and skewed by an external slope control signal;

an offline time delay tuning control (TDTC) element (202) for receiving signal samples output from the inline variable lobe filter structure (VLFS) 201 to control a first variable time delay element (T) 205 of the inline variable lobe filter structure (VLFS) 201 to provide said controlled variable time delay to generate said broadband RF tuning filter and to further control a second variable time delay element (2nT) 208 of the inline variable lobe filter structure (VLFS) 201 to provide said controlled variable time delay to generate said slope control filter lobe; and

b) adaptive control loop (6) for adjusting a complex weighting of a delayed coupled signal to maximally cancel a propagated received signal (30).

18. The interference cancellation system of claim 17, wherein the inline variable lobe filter structure (VLFS) (201) comprises:

a) said first variable time delay element (T) (205) for providing broadband tuning of an imaginary tuning filter lobe; and

b) a second variable time delay line (2nT) (208), added to first variable time delay element (205), for providing more narrowband tuning of the imaginary tuning filter lobe relative to said first variable time delay element (T) (205);

wherein said narrowband tuning filter is skewed by an external slope control signal.

19. The interference cancellation system of claim 18, wherein the second variable time delay line (2nT) 208 is an integer multiple of said first time delay line (T) (205).

20. The interference cancellation system of claim 17, wherein the adaptive control loop (6) comprises:

a reference port (9) for receiving the antenna signal (30);

an auxiliary port (8) for receiving a delayed and matched coupled signal (57);

a complex correlator (66) for generating error correlation signal (72) an integrator (67) to smooth transients on the error correlation signal (72) to form the adaptive weight control signals(73);

a complex phase and amplitude weighting device (68) having a first input and a second input, said first input receiving said delayed and matched coupled signal (57), said second input receiving a complex adaptive weight control signal (73) to weight the delayed and matched coupled signal (57) to produce a weighted delayed coupled signal (65);

forming the weighted delayed signal as a mirrored image of the transmitted reference signal; and

a summing junction (70) having a first and second input, said first input for receiving said weighted delayed coupled signal (65) output from said complex phase and amplitude weighting device (68), said second input for receiving a antenna reference signal (71) to yield a protected output (58).

21. The interference cancellation system of claim 20, wherein said antenna signal (30) comprises at least a transmission signal (40) transmitted from a first antenna (2) and received at a second antenna (4), wherein said transmission signal, contained in antenna signal (30) is propagated through an uncontrolled path between said first (2) antenna and said second (4) antenna.

22. The interference cancellation system of claim 20, wherein said forming the weighted delayed coupled signal (65) as a mirrored image of the transmitted reference signal indicates that it is equal in amplitude and 180°

out of phase with the received portion of the transmitted signal 40 in the antenna reference signal (71).

23. The interference cancellation system of claim 20, wherein said reference signal (30) includes at least one other signal.

24. The interference cancellation system of claim 23, wherein the at least one other signal is a desired signal anticipated by a protected receiver (25).