Nonreciprocal Horn Antennas Using Angular Momentum-Biased Metamaterial Inclusions

In this work, we apply angular momentum-biased metamaterials to break the intrinsic reciprocity of antenna systems, with potential applications to satellite communications. We focus our attention on a conical horn antenna exhibiting nonreciprocal response for left-handed and right-handed circularly polarized fields. A metallic screen with an annular aperture is placed between the feeding waveguide and the horn. This inclusion is loaded with modulated capacitors to achieve a nonreciprocal transmittance for circularly polarized fields impinging from opposite sides. We present the analysis of the nonreciprocal annular inclusion and explain its nonreciprocal response, obtained through proper spatiotemporal modulation, with the help of an equivalent transmission-line representation. A possible practical implementation of the modulation circuit based on band-pass and band-stop filters is also discussed. The electrical and radiating performance of the conical horn is numerically evaluated, showing the ability of the proposed antenna to filter signals with same polarization in two separate bands, e.g., uplink and downlink bands of a satellite link, depending on the propagation direction of the signal. These results may pave the way to several interesting applications of nonreciprocal radiators in satellite and radar systems.