Digital modular adaptive antenna and method

• US 6,823,174 B1
• Filed: 10/11/1999
• Issued: 11/23/2004
• Est. Priority Date: 10/11/1999
• Status: Expired due to Term

• Current Assignee: Axiom Microdevices Incorporated (Skyworks Solutions Incorporated)
• Original Assignee: Ditrans IP, Inc.
• Inventors: Masenten, Wesley K., Dell-Imagine, Robert A.
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): SOBUTKA, PHILIP
• Application Number:
  US09/415,699
• Time in Patent Office: 1,870 Days
• Field of Search: 455/562.1, 455/63.1, 455/63.4, 455/25, 455/137-139, 455/272.3, 455/276.1, 455/303, 342/16-18, 342/19, 342/379, 342/381, 342/384, 342/368-371, 342/372, 375/346, 375/347, 375/296, 375/297
• US Class Current: 455/63.4
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling

Abstract

An adaptive antenna is implemented using a plurality of modular array element modules. Each array element module comprises an antenna element of the adaptive antenna. Each antenna element is coupled to a weighting circuit is also coupled to a previous weighting circuit within a previous array element module in a concatenated manner. Each weighting circuit is configured to apply a complex weight to the antenna samples and add the result to the output of the previous weighting circuit. Each antenna element is also coupled to a cross-correlation measurement circuit configured to cross-correlate antenna samples with adaptation error samples to provide cross-correlation measurement samples to a controller which determines a weight applied by the weighting circuit.

Claims

1. A method of adapting an antenna beam to current operating conditions comprising:

determining a maximum gain value of a sidelobe region of an adaptive antenna pattern and a corresponding angle at which said maximum gain value is achieved;

determining a min-max gradient of said adaptive antenna pattern at said corresponding angle;

determining a next value of a first partial weighting value according to a current value of said first weighting value, a first predetermined step size, a first predetermined decay constant and said min-max gradient, wherein said next value of said first partial weighting value tends to limit said maximum gain value within said sidelobe region;

determining a null-steering gradient of an adaptation error based upon a set of cross-correlation measurement samples reflecting said current operating conditions;

determining a next value of a second partial weighting value according to a current value of said second partial weighting value, a second predetermined step size, a second predetermined decay constant and said null-steering gradient, wherein said next value of said second partial weighting value tends to steer a null in the direction of an interfering signal received through said sidelobe region; and

updating a beamforming weight based upon said next value of said first partial weighting value and said next value of said second partial weighting value.

2. The method of claim 1, wherein said next value of said first partial weighting value to maintain a relatively uniform gain within said sidelobe region.

3. The method of claim 1, wherein determining said maximum gain value of said adaptive antenna pattern comprises calculating said adaptive antenna pattern open loop.

4. The method of claim 1, wherein calculating said adaptive antenna pattern open loop is executed according to:

${\underset{\_}{E}}_k<br><br>\left({\mathrm{\theta <br><br>}}_k,{\mathrm{\Phi <br><br>}}_k\right)=\underset{m-1}{\overset{M}{\sum <br><br>}}<br><br>{\underset{\_}{W}}_{k,m}<br><br>\left(i\right)<br><br>{\mathrm{<br><br>}}^{j<br><br>\left[m<br><br>\left(\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}\right)·<br><br>d<br><br>\left(\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\theta <br><br>}}_k-\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Phi <br><br>}}_k\right)\right]}$

wherein;

E_k(θ

_k, Φ

_k) represents a gain value of said adaptive antenna pattern at an evaluation angle, θ

_k;

d is the distance between antenna elements of an antenna array producing said antenna beam in meters;

λ

is the wave length of a receive signal in meters.

Φ

_k is the center angle of a main beam of said adaptive antenna pattern with respect to boresight; and

θ

_k is said evaluation angle at which said gain value is evaluated.

5. The method of claim 4, wherein determining said min-max gradient is executed according to:

${\underset{\_}{\mathrm{\Gamma <br><br>}}}_m<br><br>\left(i-1,{\mathrm{\theta <br><br>}}_{k-\mathrm{Max}},{\mathrm{\Phi <br><br>}}_k\right)=<br><br>{\underset{\_}{E}}_k<br><br>\left({\mathrm{\theta <br><br>}}_{k-\mathrm{Max}},{\mathrm{\Phi <br><br>}}_k\right)<br><br><br><br>{\mathrm{<br><br>}}^{j<br><br>\left[m·<br><br>\left(\frac{2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\pi <br><br>}}{\mathrm{\lambda <br><br>}}\right)·<br><br>d<br><br>\left(\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\theta <br><br>}}_{k-\mathrm{Max}}-\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Phi <br><br>}}_k\right)\right]}$

wherein;

Γ

_m(I−

1, θ

_k-Max) is said min-max gradient;

θ

_k-Max is approximately said corresponding angle; and

E_k(θ

_k-Max, Φ

_k) is said maximum gain value of said adaptive antenna pattern at said corresponding angle, θ

_k-Max.

6. The method of claim 5, wherein said determining said next value of said first partial weighting value is executed according to:

7. The method of claim 1, wherein determining said null-steering gradient of said adaptation error comprises measuring a level of current energy received through said antenna beam and mathematically applying a transfer characteristic of a phantom auxiliary beam.

8. The method of claim 1, wherein determining said null-steering gradient of said adaptation error is executed according to:

${\underset{\_}{\mathrm{\Lambda <br><br>}}}_{k,q}<br><br>\left(i\right)=\underset{m=q}{\overset{P+q}{\sum <br><br>}}<br><br>{\underset{\_}{D}}_{k,m}<br><br>{\underset{\_}{C}}_{k,m}<br><br>\left(i\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{for}<br><br>\text{\hspace{1em}<br><br>}<br><br>q=1<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{to}<br><br>\text{\hspace{1em}<br><br>}<br><br>Q$

wherein;

Λ

_k,q(i) is said null-steering gradient of said adaptation error for a q^th phantom auxiliary beam for said antenna beam (k);

C_k,m(i) is a cross-correlation measurement sample set of signal energy received each array element, m, of an antenna array cross-correlated with energy in a compensated output of said antenna beam;

D_k,p(i) is a complex weight which determines a contribution of a p^th array element to said q^th phantom auxiliary beam for said antenna beam;

Q is a total number of said phantom auxiliary beams; and

.

P is a total number of array elements used to create each of said phantom auxiliary beams, q.

9. An apparatus which produces an antenna beam which adapts to current operating conditions comprising:

means for determining a maximum gain value of a sidelobe region of an adaptive antenna pattern and a corresponding angle at which said maximum gain value is achieved;

means for determining a min-max gradient of said adaptive antenna pattern at said corresponding angle;

means for determining a next value of a first partial weighting value according to a current value of said first weighting value, a first predetermined step size, a first predetermined decay constant and said min-max gradient, wherein said next value of said first partial weighting value tends to limit said maximum gain value within said sidelobe region;

means for determining a null-steering gradient of an adaptation error based upon a set of cross-correlation measurement samples reflecting said current operating conditions;

means for determining a next value of a second partial weighting value according to a current value of said second partial weighting value, a second predetermined step size, a second predetermined decay constant and said null-steering gradient, wherein said next value of said second partial weighting value tends to steer a null in the direction of an interfering signal received through said sidelobe region; and

means for updating a beamforming weight based upon said next value of said first partial weighting value and said next value of said second partial weighting value.

10. An adaptive antenna system comprising:

a plurality of array element modules, each of which comprises

an antenna element having an output

a programmable delay element having an input coupled to said output of said antenna element and configured to produce a delayed output

a weighting circuit having an antenna sample input coupled to said delayed output of said programmable delay element and having a composite signal input and a composite signal output, wherein said weighting circuit is coupled to a previous weighting circuit within a previous array element module in a concatenated manner such that said composite signal output from said previous weighting circuit is coupled to said composite signal input of said weighting circuit and wherein said weighting circuit is configured to apply a complex weight to samples received from said antenna sample input to produce weighted antenna samples, add said weighted antenna samples to samples received from said composite signal input and to provide a resultant signal to said composite signal output

a second delay element having an input coupled to said output of said antenna element and having a delayed output

a cross-correlation measurement circuit having an antenna sample input coupled to said delayed output of said second delay element and having an adaptive error input and a cross-correlation measurement output, wherein said cross-correlation measurement circuit is configured to cross-correlate samples received from said antenna sample input with samples received from said adaptive error input to provide cross-correlation measurement samples to said cross-correlation measurement output; and

an adaptation controller having a controller input coupled to said cross-correlation measurement output of said cross-correlation measurement circuit within each of said plurality of array element modules and a weighting output, said adaptation controller configured to determine said complex weight to provide said weighting circuit within each of said plurality of array element modules based upon said cross-correlation samples at said controller input and to provide said complex weight at said weighting output.

11. The adaptive antenna system of claim 10, wherein said cross-correlation measurement circuit further has a delayed adaptive error output configured to provide a delayed version of said samples received from said adaptive error input, wherein said cross-correlation measurement circuit is coupled to a previous cross-correlation measurement circuit within said previous array element module in a concatenated manner such that said delayed adaptive error output from said previous cross-correlation measurement circuit is coupled to said adaptive error input of said cross-correlation measurement circuit.

12. The adaptive antenna system of claim 11, wherein said composite signal output of a last weighting circuit within a last one of said plurality of array element modules is coupled to said adaptive error input of a first cross-correlation measurement circuit within a first one of said plurality of array element modules.

13. The adaptive antenna system of claim 10, wherein each of said plurality of array element modules comprises a plurality of said weighting circuits and a plurality of said cross-correlation measurement circuits, each pair of which corresponds to one of K antenna beams.

14. The adaptive antenna system of claim 10, wherein said adaptation controller is configured to determine said complex weight using a min-max adaptation algorithm which tends to limit a maximum gain value within a sidelobe region said antenna beam and a null steering adaptation algorithm which tends to steer a null in the direction of an interfering signal received through said sidelobe region.