SIW-Fed Patch Array Filtenna With Significant Suppression of Adjacent 5G Spectrum for Radio Altimeters

We propose a
$2\times2$
patch array filtenna specifically designed for radio altimeter applications with significant suppression of unwanted adjacent 5G spectrum signals. The patch radiator is carefully selected to meet the radiation requirement of radio altimeters and the substrate integrated waveguide (SIW) feeding network is meticulously designed to provide shielding property and excellent suppression level for adjacent 5G spectrum through the evanescent mode characteristic. In specific, the proposed filtenna harnesses inherent suppression characteristic of low-band RF signals below a cutoff frequency in the SIW feeding network, eliminating the need for additional filtering geometries. The proposed filtenna is fabricated and measured, and experimental results confirm its effective operation in the radio altimeter band (4.2–4.4 GHz), exhibiting successful suppression of 5G spectrum (3.4–4 GHz) by 40.70-dB to 43.26-dB. Comparative analysis reveals that the proposed filtenna demonstrates superior suppression level for adjacent spectrums compared to previous planar array filtennas.