Synthesis Design of Low-Loss and Self-Packaged Bandpass Filter on λ/4 SISL Resonators Using the Short-Open-Load (SOL) Technique

In this article, an efficient and accurate synthesis design method for bandpass filters (BPFs) based on low-loss quarter-wavelength ( $\lambda $ /4) substrate integrated suspended line (SISL) resonators is proposed, using the short-open-load (SOL) calibration technique. The BPF topology is comprised of SISL with two volumes of vias on both side walls and alternating SISL-based J/K inverters. First, with the help of full-wave simulation, the propagation characteristics of the SISL with periodically loaded pins are analyzed and extracted by SOL. Afterward, to facilitate the filter synthesis design, the equivalent circuit parameters of each J/K inverter with symmetrical/asymmetrical feed lines are accurately extracted. Herein, the extra transition for circuit measurement can be directly merged into the input port of the $J_{01}$ inverter and then be regarded as an error box to be calibrated out by SOL. Therefore, the efficient co-design of the resultant SISL BPF containing the feed transition can be achieved. Finally, two 4th-order all-pole Chebyshev SISL BPFs with $\lambda $ /4 resonators are designed and fabricated. The synthesized, simulated, and measured results of all the implemented SISL BPFs are found in good agreement, evidently demonstrating the effectiveness of the SOL technique for designing the SISL circuits. In addition, the SISL BPFs have the advantages of low loss and self-packaging against traditional planar BPFs.