Compact antenna system for polarization sensitive null steering and direction-finding

• US 20070293150A1
• Filed: 06/17/2005
• Published: 12/20/2007
• Est. Priority Date: 06/18/2004
• Status: Active Grant

• Current Assignee: Toyon Research Corporation
• Original Assignee: Toyon Research Corporation
• Inventors: VanBlaricum, Michael, Werner, Benjamin, Agate, Craig, Wiatt, Michael, Richen, Andrew, Larry, Thomas, Ezal, Kenan
• Granted Patent: US 7,577,464 B2
• Time in Patent Office: Days
• US Class Current: 455/25
• CPC Class Codes: G01S 3/32 derived from different combinations of signals from separate antennas, e.g. comparing sum with difference
• CPC Class Codes: H01Q 1/243 with built-in antennas
• CPC Class Codes: H01Q 21/29 Combinations of different interacting antenna units for giving a desired directional characteristic H01Q25/00 takes precedence

Abstract

A compact, non-phased-array, electronically reconfigurable antenna (ERA) system with at least two operational modes has a first operational objective that is polarization-sensitive null steering (PSNS) and a second operational objective that is direction-finding (DF). The system can rapidly switch between two operational states. In the first state, the system behaves like a polarization filter (PF) and operates as a controlled reception pattern antenna (CRPA), while in the second state the system behaves as an angle-of-arrival (AOA) sensor and operates as a fixed reception pattern antenna (FRPA). The system may include a spiral-mode antenna with both feed and load ports; a mode-forming network; an electronics package; and feedback control electronics. Radio frequency (RF) interference rejection and RF direction-finding may be performed as well as reduction and/or elimination of multiple jamming signals that are intentionally or unintentionally directed at a Global Positioning System (GPS). The determination of direction and location of the source of jamming signals may also be achieved.

Claims

1. An antenna system for use in interference suppression and direction finding, said system comprising:

an antenna element having at least two fundamental modes that can be used to derive angle-of-arrival estimates for received signals;

a plurality of load circuits embedded either in the radiation aperture of the antenna element or behind a ground plane of said antenna element, said load circuits having impedance characteristics that are either (a) predetermined and fixed or (b) variable by changing the values of electrical control signals applied to active components within the load circuits; and

a controller configured to select for use a subset of said load circuits to effect operation in at least one of said fundamental modes and which updates control settings of selected load circuits having variable impedance and belonging to said subset, if any.

2. The antenna system of claim 1, wherein the controller is configured to dynamically select the said subset and to adapt control settings of the selected load circuits having variable impedance and belonging to said subset, if any, and, thereby to adapt impedance characteristics of the antenna element to produce front-end control of the received signals.

3. The antenna system of claim 1, wherein said fundamental modes can be used to effect operational states that include:

(a) direction finding, (b) interference suppression, and (c) combined direction finding and interference suppression.

4. The antenna system of claim 1, wherein the load circuits are configured to cause the antenna system to be resilient to detuning while at the same time enabling substantial adaptation of impedance characteristics of the variable load circuits to achieve improved performance optimization for each fundamental mode of the antenna system.

5. The antenna system of claim 1, wherein angle-of-arrival estimates of received signals are generated with improved accuracy based on estimated or measured dynamics of the antenna system.

6. The antenna system of claim 1, further comprising:

(a) means for measuring received signal angle-of-arrival by converting measured signals of at least two fundamental modes or patterns of said antenna element into angle-of-arrival measurements for the received signals;

(b) means for maintaining a track by creating new tracks for the received signals with angle-of-arrival measurements that are statistically inconsistent with the angle-of-arrival estimates of previously existing tracks, and by eliminating said existing tracks with no new statistically consistent angle-of-arrival measurements;

(c) means for tracking and updating said existing tracks to provide estimates of the dynamics for a point-of-origin of each of said received signals based on the angle-of-arrival measurements of the received signals and measured or estimated dynamics of said antenna system; and

(d) means for estimating a received signal angle-of-arrival by computing an angle-of-arrival estimate for said existing tracks based on relative dynamics of said antenna system and the point-of-origin of each of said received signals.

7. The antenna system of claim 1, wherein the largest dimension of the radiating aperture of said antenna element is no greater than about three-quarters wavelength at the lowest frequency of its operational band.

8. A controlled antenna system for use in interference suppression and direction finding, said system comprising:

a loaded antenna element having at least two fundamental modes that can be used to derive angle-of-arrival estimates for received signals, wherein the largest dimension of the radiating aperture of the antenna element is no greater than about three-quarters wavelength at the lowest frequency of its operational band;

a plurality of control circuits embedded either in the radiation aperture of the antenna element or behind a ground plane of said antenna element, said control circuits having impedance characteristics that are either (a) predetermined and fixed or (b) variable by changing values of electrical control signals applied to active components within the control circuits;

wherein said control circuits are divided into at least two subsets, with impedance characteristics of each of said subsets being dependent on whether the subset is used for (a) direction finding, (b) interference suppression, or (c) combined direction finding and interference suppression;

means for activating any selected one of said subsets of control circuits by effectively electrically connecting the selected subset to said antenna element while effectively disconnecting control circuits not belonging to said subset from said antenna element; and

a dynamic feedback controller which is configured to dynamically select a subset of said control circuits for activation, and which regularly updates control settings of selected control circuits having variable impedance and belonging to said active subset, if any.

9. The antenna system of claim 8, wherein said controller receives a sequence of bias estimate values and uses these to set updated voltage biases that are applied to active components in the control circuits belonging to said active subset, if any.

10. The antenna system of claim 8, wherein controller outputs are determined to obtain a maximum, minimum or a predetermined value for one or more antenna system metrics.

11. A method for controlling a single element antenna system for use in interference suppression and direction finding having at least two fundamental modes and having a plurality of load circuits embedded either in the radiation aperture of the antenna element or behind a ground plane of said antenna element, said load circuits having impedance characteristics that are either (a) predetermined and fixed or (b) variable by changing the values of electrical control signals applied to active components within the load circuits, said method comprising:

converting antenna outputs for said at least two fundamental modes of said antenna element into angle-of-arrival estimates for received signals;

selecting a subset of said load circuits and regularly updating control settings of selected load circuits having variable impedance and belonging to said subset, if any; and

connecting said selected subset of load circuits electrically to the antenna element while disconnecting load circuits not belonging to said subset from said antenna element.

12. The method of claim 11, wherein the selecting and controlling steps adapt control settings of load circuits having variable impedance and belonging to said subset and thereby adapts impedance characteristics of the antenna element so as produce front-end control of received signals.

13. The method of claim 11, wherein said load circuits are divided into at least two subsets and wherein the selection of a subset of load circuits depends on an operational state of the antenna system including:

(a) direction finding, (b) interference suppression, or (c) combined direction finding and interference suppression.

14. The method of claim 11, wherein the load circuits cause the antenna system to be resilient to detuning while at the same time enabling substantial adaptation of impedance characteristics of variable load circuits to achieve improved performance optimization for each said fundamental mode of the antenna system.

15. The method of claim 11, wherein accuracy of the angle-of-arrival estimates of the received signals is improved by using estimated or measured dynamics of the antenna system.

16. The method of claim 11, further comprising:

converting measured signals for at least two of said fundamental modes or patterns of said antenna element into angle-of-arrival measurements for the received signals;

creating new tracks for the received signals with said angle-of-arrival measurements that are statistically inconsistent with the angle-of-arrival estimates of previously existing tracks;

eliminating said existing tracks with no new statistically consistent angle-of-arrival measurements;

combining said angle-of-arrival measurements and measured or estimated dynamics of said antenna system to update existing tracks and provide estimates of dynamics for a point-of-origin of each of said received signals; and

computing an angle-of-arrival estimates for said existing tracks based on relative dynamics of said antenna system and the point-of-origin of each of said received signals.

17. The method of claim 11, wherein the largest dimension of the radiating aperture of said antenna element is no greater than about three-quarters wavelength at the lowest frequency of its operational band.

18. A method for controlling a single element loaded antenna system for use in interference suppression and direction finding, said antenna system having at least two fundamental modes, a largest dimension no greater than about three-quarters wavelength at the lowest frequency of its operational band, and a plurality of control circuits embedded either in the radiation aperture of the antenna element or behind a ground plane of said element, said control circuits having impedance characteristics that are either (a) predetermined and fixed or (b) variable by changing the values of electrical control signals applied to active components within the control circuits, wherein said control circuits are divided into at least two subsets, with impedance characteristics of each of said subsets being dependent on whether the subset is to be used for direction finding, interference suppression, or combined direction finding and interference suppression, said method comprising:

converting fundamental mode outputs of said element into angle-of-arrival estimates for received signals;

dynamically selecting a subset of said control circuits for activation and regularly updating the control settings of selected control circuits having variable impedance and belonging to said active subset, if any; and

connecting said active subset electrically to said antenna element while disconnecting remaining control circuits not belonging to said active subset from said antenna element;

wherein dynamic feedback control adapts biases applied to control circuits having variable impedance and belonging to said active subset, if any, thereby adapting impedance characteristics of the antenna element to produce front-end control of the received signals; and

wherein feedback at regular intervals is used to generate and output at regular intervals updated estimates of bias setting values.

19. The method of claim 18, further comprising:

converting measured signal outputs for at least two fundamental modes or patterns of said antenna element into angle-of-arrival measurements for the received signals;

creating new tracks for the received signals with said angle-of-arrival measurements that are statistically inconsistent with the angle-of-arrival estimates of previously existing tracks; and

eliminating said existing tracks with no new statistically consistent said angle-of-arrival measurements;

combining said angle-of-arrival measurements and measured or estimated dynamics of said antenna system to update said existing tracks that provide estimated dynamics for a point-of-origin for each of the received signals; and

computing the angle-of-arrival estimates for said existing tracks based on relative dynamics of said antenna system and the point-of-origin of each of the received signals.

20. The method of claim 18, wherein command input signals are provided at regular intervals by a receiver which computes the command input signals based on output signals from said antenna system.