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A low profile antenna system includes an artificial magnetic conductor comprising a frequency selective surface (FSS) having an effective sheet capacitance which is electronically variable to control resonant frequency of the AMC and the resonant frequency of an antenna element positioned adjacent t

A low profile antenna system includes an artificial magnetic conductor comprising a frequency selective surface (FSS) having an effective sheet capacitance which is electronically variable to control resonant frequency of the AMC and the resonant frequency of an antenna element positioned adjacent to the FSS.

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1. An antenna system comprising:an artificial magnetic conductor (AMC) including a frequency selective surface (FSS) including voltage variable capacitive elements to give the FSS an effective sheet capacitance which is variable to control resonant frequency of the AMC; and an antenna element positi

1. An antenna system comprising:an artificial magnetic conductor (AMC) including a frequency selective surface (FSS) including voltage variable capacitive elements to give the FSS an effective sheet capacitance which is variable to control resonant frequency of the AMC; and an antenna element positioned adjacent to the FSS. 2. The antenna system of claim 1 wherein the antenna element comprises an antenna having instantaneous bandwidth of one octave or greater in free space.3. The antenna system of claim 1 wherein the antenna element comprises:a tuned narrowband antenna. 4. The antenna system of claim 1 wherein the antenna element comprises a bent wire monopole antenna.5. The antenna system of claim 1 wherein the antenna element comprises a spiral antenna flush mounted with the FSS.6. The antenna system of claim 1 wherein the antenna element comprises a bowtie antenna.7. The antenna system of claim 6 wherein the antenna element comprises a log-periodic bowtie antenna.8. The antenna system of claim 1 wherein the FSS comprises:one or more layers of capacitively coupled conductive patches. 9. The antenna system of claim 8 further comprising:one or more variable capacitance elements integrated into the FSS. 10. An antenna system comprising:an artificial magnetic conductor (AMC) including a frequency selective surface (FSS), a conductive backplane structure, a spacer layer separating the conductive backplane structure and the FSS, the spacer layer including conductive vias extending between the conductive backplane structure and the FSS, and voltage variable capacitive circuit elements coupled with the FSS and responsive to one or more bias signal lines routed through the conductive backplane structure and the conductive vias; and an antenna element positioned adjacent to the AMC. 11. The antenna system of claim 10 wherein the antenna element comprises a bent wire monopole antenna.12. The antenna system of claim 10 wherein the antenna element comprises a spiral antenna flush mounted with the FSS.13. An antenna system comprising:an artificial magnetic conductor (AMC) including a frequency selective surface (FSS) including a periodic array of conductive patches; a space layer including vias extending therethrough in association with predetermined conductive patches of the FSS; and a conducting backplane structure including two or more bias signal lines, the AM characterized by a unit cell including in a first lane, a pattern of three or more conductive patches, one conductive patch electrically coupled with an associated conductive via, and voltage variable capacitive elements between select laterally adjacent conductive patches; and a conductive backplane segment extending in a second plane substantially parallel to a plane including the three or more conductive patches and the associated conductive via extending from the one conductive patch to one of the two or more bias signal lines; and an antenna element positioned adjacent to the AMC. 14. The antenna system of claim 13 wherein the antenna element comprises a bent wire monopole antenna.15. The antenna system of claim 13 wherein the antenna element comprises a spiral antenna flush mounted with the FSS.16. A method for tuning an antenna system which includes an antenna element adjacent to an artificial magnetic conductor (AMC) having a frequency selective surface (FSS) which has a pattern of conductive patches, a conductive backplane structure and a spacer layer separating the FSS and the conductive backplane structure, the method comprising:applying bias control signals to voltage variable capacitive elements associated with the FSS; and thereby, reconfiguring effective sheet capacitance of the FSS to tune the antenna. 17. The method of claim 16 wherein applying bias control signals comprises applying the bias control signals to conductors located in the conductive backplane structure and coupled to selected conductive patches by conductors extending through the spacer layer.18. The method of claim 16 further comprising:tuning a resonant frequency of the AMC. 19. An antenna system comprising:an artificial magnetic conductor (AMC) comprising a frequency selective surface (FSS) having a pattern of conductive patches, a conductive backplane structure, and a spacer layer separating the FSS and the conductive backplane structure, the spacer layer including conductive vias associated with some but not all patches of the pattern of conductive patches; and an antenna positioned an effective distance from the FSS. 20. The AMC of claim 19 wherein the conductive backplane structure comprises at least one ground plane, the conductive vias being in electrical contact with the at least one ground plane.21. The AMC of claim 19 wherein the FSS comprises:a first set of conductive patches on one side of an FSS dielectric layer, and a second set of conductive patches on a second side of an FSS dielectric layer. 22. The AMC of claim 21 wherein the spacer layer has conductive vias associated with some or all of only the first set of conductive patches.23. The AMC of claim 22 wherein the spacer layer has conductive vias associated with some or all of only the second set of conductive patches.24. The AMC of claim 19 wherein the conductive backplane structure comprises bias signal lines in electrical contact with at least a subset of the conductive vias.25. The AMC of claim 24 wherein the conductive backplane structure further comprises at least one ground plane, at least a second subset of the conductive vias being in electrical contact with the at least one ground plane.26. The AMC of claim 19 wherein the FSS comprises:a layer of conductive patches on one side of a dielectric layer. 27. The AMC of claim 19 wherein the FSS comprises:a layer of conductive patches on one side of a tunable dielectric layer. 28. The AMC of claim 19 wherein the FSS comprises:a first layer of conductive patches on one side of a tunable dielectric film; and a second layer of conductive patches on a second side of the tunable dielectric film. 29. The AMC of claim 28 wherein the spacer layer comprises:a first set of conductive vias associated with at least some patches of the first layer of conductive patches; and a second set of conductive vias associated with at least some patches of the second layer of conductive patches. 30. An antenna system comprising:an antenna; and a high impedance surface adjacent the antenna, the high impedance surface comprising: a frequency selective surface (FSS) patterned with conductive patches; a conductive ground plane; and a layer separating the FSS and the conductive backplane structure, the layer including a dielectric material pierced by a partial forest of conductive vias. 31. The antenna system of claim 30 wherein the antenna comprises a bent wire monopole antenna.32. The antenna system of claim 30 wherein the antenna comprises a spiral antenna flush mounted with the FSS.33. The antenna system of claim 30 wherein the antenna comprises a bowtie antenna.