Fabrication-Tolerant Reconfigurable AFSIW Filters Based on Through-Hole Mounted Metallic Posts for Versatile High Performance Systems
A novel structure of air-filled substrate integrated waveguide (AFSIW) filters based on through-hole mounted metallic posts is presented. It is based on standard and low-cost printed circuit board (PCB) process, through-hole technology and FR-4 substrate. First, a theoretical study of coupling windows for the synthesis of the proposed filter topology is introduced. Then, for demonstration purposes, two four-order bandpass filters with center frequency of 20 and 21 GHz and -3 dB bandwidth of 500 and 400 MHz, respectively, are synthesized. A Monte Carlo analysis shows that the proposed structure is fabrication-tolerant while filters based on milled coupling iris windows require post-process tuning. For experimental validation, a single reconfigurable transmission line structure able to implement both synthesized filters is demonstrated. In its transmission line configuration, it achieves a -20 dB return loss with a 0.1 dB insertion loss in the 15 to 22 GHz frequency range. In its filter configurations, obtained mounting the appropriate metallic posts, both filters achieve insertion loss as low as 0.7 dB and 0.73 dB, respectively, with return loss of better than -19 dB and -20 dB, respectively, without any post-process tuning. This topology is of particular interest for versatile and high performance microwave and millimeter-wave circuits and systems based on the AFSIW technological platform.