Isolated Filtering System Based on the Emerging AFSIW Technology

This paper introduces a pioneering passive system in the promising air-filled substrate integrated waveguide (AFSIW) technology. The designed single printed circuit board (PCB) system integrates a filter surrounded by two isolators strategically arranged to mitigate impedance mismatching at its interface and provide high isolation. To do this, the filter and the isolators were designed separately and then assembled together to achieve optimal performance in the satellite Ka frequency band (from 27.5 GHz to 30.2 GHz) with a matching better than 20 dB. A demonstrator was simulated and manufactured for validation. It consists of two isolators and one 8
^th
order filter centered at 28.88 GHz with 2.94 GHz bandwidth (BW). The measured demonstrator achieves high rejection with 1.32 dB insertion losses (IL) at the filter center frequency. A frequency shift of 340 MHz and a return loss better than 13 dB were obtained in the experiment. The discrepancy between this first demonstrator and the simulation results is due to fabrication errors, which could be effectively compensated by considering the tolerances of the manufacturing process and implementing some tuning elements in future designs. To the best of the authors’ knowledge, it is the first time a passive system based on the AFSIW technology is reported.