Highly Selective and Compact Filtering Antennas Using Dual-Mode SIW Resonators

A novel class of compact and highly selective filtering antennas controlling two finite position transmission zeros (TZs) are presented. The filtering antennas are composed of a substrate-integrated waveguide (SIW) filtering doublet and a wideband cavity backed slot antenna (CBSA). Design guidelines are presented to implement bandpass filtering antennas with TZ: above, below, or on opposite sides of the passband. The TZ location is highly flexible relative to the passband and is entirely determined by the input feed offset and via position. Stand-alone devices demonstrating the three via arrangements are presented around 16 GHz. All devices demonstrate a flat passband gain around 5 dB with a single element, direct control over the TZ position, high passband roll-off and out-of-band (OOB) attenuation, and low cross polarization. Compared with the state-of-the-art SIW filtering antennas, the fabricated devices demonstrate the highest combined bandwidth, passband roll-off, and OOB attenuation. In addition, the device with TZ on either side of the passband is sequentially rotated in a <inline-formula> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> topology to form a right-handed circularly polarized (RHCP) filtering array with a flat passband gain around 9 dB, retaining the high selectivity.