Near-field gradient probe for the suppression of radio interference

• US 9,812,790 B2
• Filed: 04/02/2015
• Issued: 11/07/2017
• Est. Priority Date: 06/23/2014
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Lavedas, Thomas G.
• Primary Examiner(s): Duong, Dieu H
• Assistant Examiner(s): Bouizza, Michael
• Application Number:
  US14/677,130
• Publication Number:
  US 20150372395A1
• Time in Patent Office: 950 Days
• CPC Class Codes: G01N 24/084 Detection of potentially hazardous samples, e.g. toxic samples, explosives, drugs, firearms, weapons
• CPC Class Codes: G01R 33/3415 comprising arrays of sub-coils , i.e. phased-array coils with flexible receiver channels
• CPC Class Codes: G01R 33/3642 Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification
• CPC Class Codes: G01R 33/441 Nuclear Quadrupole Resonance [NQR] Spectroscopy and Imaging
• CPC Class Codes: H01Q 1/521 reducing the coupling between adjacent antennas
• CPC Class Codes: H01Q 21/28 Combinations of substantially independent non-interacting antenna units or systems multiple beam H01Q25/00
• CPC Class Codes: H01Q 7/005 with variable reactance for tuning the antenna
• CPC Class Codes: H01Q 7/02 Collapsible antennas; Retractable antennas

Abstract

An antenna system is provided comprising first, second, and third loop antennas, each antenna having a respective loop area and spaced apart from the other antennas. The first and third antennas are configured and driven to form a first independent balanced feed point that is substantially isolated from the second antenna, which is configured to be driven from a second balanced feed point. A sum of the first and second respective loop areas, at a sum port in operable communication with the first and second balanced feed points, is substantially equivalent to the third respective loop area. An automatic control system is configured to automatically and independently adjust, via the balanced feed points, at least one of amplitude and phase for at least one of the three loop antennas, to help to substantially maximize suppression of RFI for a sum of signals from the first and second balanced feed points.

Claims

1. An antenna system, comprising:

a first loop antenna comprising a first conductor forming a first loop, the first loop having a first respective loop area;

a second loop antenna spaced apart from the first loop antenna, the second loop antenna comprising a second conductor forming a second loop, the second loop antenna having a second respective loop area;

a third loop antenna spaced apart from both the first and second loop antennas, the third loop antenna comprising a third conductor forming a third loop having a third respective loop area, wherein;

the first and third loop antennas are operably coupled together in electrical opposition to each other, configured to be driven to form a first independent balanced feed point, and configured to be substantially electrically and magnetically isolated from the second loop antenna;

the second loop antenna is configured to be driven from a second balanced feed point;

the first, second and third loops are configured such that a sum of the first and second respective loop areas, at a sum port in operable communication with the first and second balanced feed points, is substantially equivalent, within a predetermined tolerance, to the third respective loop area; and

the first and second balanced feed points are in operable communication with an automatic control system configured to automatically and independently adjust at least one of amplitude and phase for at least one of the first, second, and third loops in operable communication with at least one of the first and second balanced feed points, where each respective automatic and independent adjustment is configured to help to substantially maximize suppression of radio frequency interference (RFI) for a sum of signals from the first and second balanced feed points.

2. The antenna system of claim 1, wherein the automatic control system comprises:

a first amplitude adjustment circuit under automatic control and in operable communication with a respective one of the first and second loops; and

a first phase adjustment circuit under automatic control and in operable communication with a respective one of the first and second loops;

wherein the first amplitude adjustment circuit is configured to operate independently of the first phase adjustment circuit.

3. The antenna system of claim 1, wherein the automatic control system further comprises a first tune/match adjustment circuit in operable communication with an automatic control and a respective one of the first and second loops, the tune/match adjustment circuit responsive to a first control signal configured to provide tuning of the respective one of the first and second loops, the tuning configured to adjust a resonant frequency of the respective one of the first and second loops.

4. The antenna system of claim 1, wherein the automatic control system further comprises a first tune/match adjustment circuit in operable communication with an automatic control and a respective one of the first and second loops, the first tune/match adjustment circuit configured to provide phase matching for the respective one of the first and second loops.

5. The antenna system of claim 1, wherein the antenna system is in operable communication with a mechanical control configured to adjust a size of one of the first, second, and third loops,

wherein the adjustment provided by the mechanical control cooperates with one or more of the adjustments performed by the automatic control system, to help to substantially maximize suppression of RFI.

6. The antenna system of claim 1, wherein the first loop comprises an inner loop, the second loop comprises a middle loop, and the third loop comprises an outer loop.

7. The antenna system of claim 6, wherein, for a given inter-loop ratio factor K, the inter-loop ratios are defined as follows:

8. The antenna system of claim 7, wherein K is between about 1.125 to about 1.25.

9. The antenna system of claim 1, wherein at least two of the first, second, and third loops have substantially similar shapes.

10. The antenna system of claim 1, wherein at least two of the first, second, and third loops are substantially concentric.

11. The antenna system of claim 1, wherein at least one of the first, second, and third loops comprises a respective set of two or more sub-loops, each sub-loop having a respective sub-loop area, wherein the sum of all the respective sub loop areas in the respective set is substantially equivalent to the respective loop area of the at least one of the first, second and third loops.

12. The antenna system of claim 1, wherein the first, second and third loops are substantially coplanar.

13. The antenna system of claim 1, wherein the first and third loops are substantially coplanar and lie within a first plane, and the second loop lies within a second plane that is spaced apart from but parallel to the first plane.

14. The antenna system of claim 1, wherein:

(a) if any two of the first, second, and third loops have substantially the same respective loop area as each other, then a first spacing S1 is defined as being between the two loops having substantially the same respective loop area; and

(b) if the respective loop areas of any two of the first, second and third loops, when added together, form a pair of loops that together have substantially the same loop area as the remaining one of the first, second and third loops, then a second spacing S2 is defined as being between either one of the pair of loops and the remaining one of the first, second, and third loops;

wherein at least one of S1 and S2 is selected to help to maximize RFI suppression at a given operational frequency λ

, where;

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

a fourth loop antenna spaced apart from the first, second, and third loop antennas, wherein the first, second, third and fourth the fourth loop antennas are substantially concentric and coplanar, wherein the fourth antenna comprises a fourth conductor forming a fourth loop that is configured to be substantially electrically and magnetically isolated from the first, second, and third loop antennas, wherein the fourth loop is configured to include a third balanced feed point that is electrically independent of the sum port of the first, second, and third loops;

wherein the first, second, and third loop antennas are configured to instantiate a selected one of a transmit and a receive function; and

wherein the fourth loop antennas is configured to instantiate the other of the transmit and receive functions, such that the fourth loop antenna performs a different function than the first, second, and third loop antennas.

16. A method of increasing suppression of radio frequency interference (RFI) in an antenna system comprising first, second, and third loops, the method comprising:

sizing the first, second, and third loops such that a sum of an area defined by the inner loop and an area defined by the second loop is substantially equivalent, within a predetermined tolerance, to an area defined by the third loop;

operably coupling the first and third loops together in electrical opposition to each other;

configuring the first and third loops to be driven from a first independent balanced feed point and to be substantially electrically and magnetically isolated from the middle loop;

configuring the second loop to be driven from a second balanced feed point; and

automatically and independently adjusting at least one of amplitude and phase for at least one of the first, second, and third loops in operable communication with at least one of the first and second balanced feed points, where each respective automatic and independent adjustment is configured to help to maximize suppression of RFI for a sum of signals from the first and second balanced feed points.

17. The method of claim 16, wherein, for a given inter-loop ratio factor K, the inter-loop ratios are defined as follows:

18. The method of claim 17, wherein K is between about 1.125 to about 1.25.

19. The method of claim 16, further comprising:

providing a fourth loop antenna spaced apart from the first, second, and third loop antennas, wherein the first, second, third and fourth the fourth loop antennas are substantially concentric and coplanar, wherein the fourth antenna comprises a fourth conductor forming a fourth loop that is configured to be substantially electrically and magnetically isolated from the first, second, and third loop antennas, wherein the fourth loop is configured to include a third balanced feed point that is electrically independent of the sum port of the first, second, and third loops;

configuring the first, second, and third loop antennas to instantiate a selected one of a transmit and a receive function; and

configuring the fourth, loop antenna to instantiate the other of the transmit and receive functions, such that the fourth loop antenna performs a different function than the first, second, and third loop antennas.

20. The method of claim 17, further comprising operably coupling the antenna system to a controller, the controller comprising at least one of an automatic electronic control and a mechanical control, wherein the controller is configured to cooperate with the automatic control system to adjust at least one of the following to help maximize suppression of RFI:

(a) a size of one of the first, second and third loops;

(b) a phase of one or both of the first and second loops;

(c) an amplitude of one or both of the first and second loops;

(d) a resonant frequency of one of the first and second loops;

(e) a phase match for one of the first and second loops; and

(g) a spacing between any two of the first, second, and third loops.