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 non-uniform 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 employs 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 (TZ) along with a fourth TZ above the second passband. The second layer employs a non-uniform MTS which acts as an equivalent radiating load. The novel non-uniform MTS is designed to adequately match both passbands providing a high and flat realized gain, 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 of 7.9% and 11.0%, each centered around 19 GHz and 27 GHz respectively. The passband's demonstrate a flat in-band realized gain around 7.7 dB and 9.8 dB respectively. Additionally, both 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 GHz, 22 GHz, 23.3 GHz and 25.1 GHz along with an additional frequency null located above the second passband at 29.5 GHz.