Quasi TEM dielectric travelling wave scanning array
A dielectric travelling wave antenna (DTWA) using a TEM mode transmission line and variable dielectric substrate.
1. An apparatus comprising:
a transverse electromagnetic mode (TEM) transmission line composed of a non-dispersive, elongated planar conductor;
a dielectric structure disposed beneath the TEM transmission line, the dielectric structure having an adjustable wave propagation constant; and
a series of antenna coupling taps, each coupling tap composed of a planar conductor disposed in a same plane as the planar conductor of the TEM transmission line, with the coupling taps further disposed such that there is a series of coupling taps on both sides of the TEM transmission line.
2. The apparatus of claim 1 wherein the dielectric structure further comprises multiple dielectric material layers spaced apart by gaps.
3. The apparatus of claim 2 additionally comprising a control element arranged to adjust a size of the gaps, and thereby affect a change in a beam angle, where the control element may be a piezoelectric, electroactive material or a mechanical position control.
4. The apparatus of claim 1 additionally comprising a delay element connected to each of two or more of the coupling taps, wherein a delay introduced by respective delay elements changes with a respective position of each coupling tap along the TEM transmission line.
5. The apparatus of claim 4 wherein a cumulative additional delay introduced by the delay elements cancels a delay introduced by the TEM transmission line.
6. The apparatus of claim 1 wherein the non-dispersive, elongated TEM transmission line is one of a stripline, microstrip, parallel plate, or slot line.
7. The apparatus of claim 1 wherein the coupling taps are positioned in orthogonal pairs, and a first coupling tap of each pair located on a first side of the transmission line is spaced apart from a second coupling tap of each pair on a second side of the transmission line by ¼ λ, where λ is an operating wavelength.
8. The apparatus of claim 1 wherein each coupling tap couples the TEM transmission line to a radiating antenna element.
9. The apparatus of claim 1 wherein the coupling taps are radiating elements.
10. The apparatus of claim 8 wherein each coupling tap is a transformer coupler with tapered widths.
11. The apparatus of claim 8 wherein each coupling tap is a TEM mode coupler.
12. The apparatus of claim 1 additionally comprising a second planar TEM transmission line disposed in the same plane as the series of coupling taps.
13. The apparatus of claim 12 additionally comprising a feed network, coupled to at least one of the TEM transmission lines to control polarization.
14. The apparatus of claim 13 additionally wherein the feed network controls RHCP and LHCP.