Dual-Band SIW Metasurface Filtering Antenna With High Inter-Band Selectivity

A highly selective dual-band filtering antenna based on a perturbed substrate integrated waveguide (SIW) cavity and a nonuniform metasurface (MTS) is presented. The structure is compact, only requiring two substrate layers while providing five radiation frequency nulls. The first layer is composed of a filtering cavity which uses the perturbed second- and third-order modes to support the two passbands. The cavity is designed to satisfy the coupling requirements of a filtering doublet, implementing three controllable inter-band transmission zeros (TZs) along with a fourth TZ above the second passband. The second layer uses a nonuniform MTS which acts as an equivalent radiating load. The novel nonuniform MTS is designed to adequately match both passbands providing a high and flat realized gain (RG), improve the higher frequency radiation patterns, retain the intrinsic filtering function, and introduce an additional inter-band radiation frequency null. A prototype is fabricated and measured demonstrating two 10-dB fractional bandwidths (FBWs) of 7.9% and 11.0%, each centered around 19 and 27 GHz, respectively. The passbands demonstrate a flat in-band RG around 7.7 and 9.8 dB, respectively. In addition, both the bands exhibit a very sharp roll-off and an inter-band attenuation greater than 26.5 dB due to the four inter-band frequency nulls at 21, 22, 23.3, and 25.1 GHz along with an additional frequency null located above the second passband at 29.5 GHz.