Near field tunable parasitic antenna

• US 9,806,420 B2
• Filed: 07/07/2015
• Issued: 10/31/2017
• Est. Priority Date: 06/12/2012
• Status: Active Grant

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: The United States of America As Represented By The Secretary of Agriculture
• Inventors: Church, Justin A., Santoyo-Mejia, Ricardo
• Primary Examiner(s): Mai, Lam T
• Application Number:
  US14/793,526
• Publication Number:
  US 20150311585A1
• Time in Patent Office: 847 Days
• Field of Search: 343741, 343745, 343749, 343797, 343866, 343848
• CPC Class Codes: H01Q 21/24 Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction circularly polarised patch antennas H01Q9/0428; circularly polarised horns H01Q13/0241; cross-polarised horns H01Q13/0258; polarisation converters H01Q15/242; cross-polarised rear feeds H01Q19/136; crossed polarisation dual antenna H01Q25/001
• CPC Class Codes: H01Q 5/35 using two or more simultaneously fed points
• CPC Class Codes: H01Q 7/005 with variable reactance for tuning the antenna

Abstract

An antenna comprising: a conductive ground plane; a conductive half loop grounded to the ground plane and configured to be fed with a radio frequency (RF) signal; a single, unitary, three-sided, conductive cage positioned so as to cover the half loop; and dielectric mounts disposed between the cage and the ground plane such that the cage is electrically insulated from the ground plane.

Claims

1. An antenna comprising:

a conductive ground plane;

a conductive half loop grounded to the ground plane and configured to be fed with a radio frequency (RF) signal;

a single, unitary, three-sided, conductive cage positioned so as to cover the half loop; and

dielectric mounts disposed between the cage and the ground plane such that the cage is electrically insulated from the ground plane.

2. The antenna of claim 1, wherein the antenna fits within an imaginary sphere having a radius a, and wherein a product ka is less than 0.5, where k is a wave number.

3. The antenna of claim 1, further comprising an even number of at least two tunable capacitors mounted to the ground plane.

4. The antenna of claim 3, wherein the dielectric mounts are attached to an upper side of the ground plane and wherein the tunable capacitors are mounted to a lower side of the ground plane.

5. The antenna of claim 3, further comprising a controller operatively coupled to the tunable capacitors such that the controller is configured to dynamically tune the antenna.

6. The antenna of claim 3, wherein there are four tunable capacitors, one mounted to each corner of the ground plane.

7. The antenna of claim 6, wherein the ground plane, loop, and conductive cage are made of copper.

8. The antenna of claim 6, wherein the ground plane, loop, and conductive cage are made of brass.

9. The antenna of claim 1, wherein the antenna does not have an external matching network.

10. The antenna of claim 9, wherein the conductive cage is comprised of a wire mesh.

11. The antenna of claim 9, wherein the conductive cage is solid.

12. The antenna of claim 1, wherein the ground plane has a width that is less than or equal to 1/12 of an operating wavelength, and wherein the conductive cage has a height that is less than or equal to 1/67 the operating wavelength.

13. The antenna of claim 12, wherein the operating frequency is 300 MHz.

14. A method for providing a tunable, electrically small antenna where ka<

0.5, where the antenna fits within an imaginary sphere having a radius a, and where k is a wave number, comprising the following steps;

providing a conductive ground plane;

grounding a conductive half loop to a center of the ground plane;

impedance matching the antenna by covering the conductive half loop with a single, unitary, three-sided, conductive cage so as to create capacitive fields that cancel inductive fields generated by the conductive half loop;

electrically insulating the conductive cage from the ground plane by disposing dielectric mounts between the conductive cage and the ground plane; and

feeding the conductive half loop with a radio frequency (RF) signal to create an omni-directional, linearly polarized radiation pattern.

15. The method of claim 14, further comprising a step of mounting an even number of at least two tunable capacitors to the ground plane.

16. The method of claim 15, further comprising a step of dynamically tuning the antenna to a desired operating frequency by tuning the capacitors.

17. The method of claim 16, wherein the tuning is performed with a microcontroller.

18. The method of claim 16, wherein the dynamic tuning step is performed in response to changing environmental conditions experienced by the antenna.

19. The method of claim 17, wherein the capacitors are all tuned simultaneously to the same picofarad setting.

20. The method of claim 16, wherein the antenna is tunable between the frequencies of 250 to 350 MHz.