Fully Shielded Half-Mode SIW Cavity-Based Compact Filtenna for 5G n257 Operations

A compact filtenna is presented in this letter based on the study on a fully shielded half-mode substrate-integrated waveguide (FSD-HMSIW) cavity. The proposed FSD-HMSIW cavity uses a shielded combined boundary instead of the open magnetic boundary, enabling radiation while preventing energy leakage into the substrate region. Resultantly, two FSD-HMSIW cavities can be closely placed to reduce the size and produce two in-band resonance poles, as well as an additional radiation null due to the electric-dominated cross coupling. By further adding a shorted concave loop, a magnetic-dominated cross coupling path can be introduced to produce a resonance pole and an extra radiation null at the lower band. The active simulation of a 1 × 8 beam scanning array verifies that the proposed compact filtenna can provide a stable bandpass filtering response over a wide beam-scanning angle of ±45°. For verification, a prototype of the proposed filtenna with a compact size of 0.32λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.32λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> was fabricated and tested, showing a wide bandwidth covering the 5G n257 band (26.5–29.5 GHz), a high peak gain of 6.8 dBi, excellent frequency selectivity, and good radiation patterns.