FR‐4‐based Ka‐band SISL bandpass filters using folded half‐wavelength resonators

Abstract

In this letter, bandpass filters (BPFs) with folded short‐circuited half‐wavelength (λ/2) resonators are proposed based on the substrate integrated suspended line (SISL) platform for satellite communications. Each λ/2 resonator is folded, to achieve an overlapping structure, which not only reduces the size, but more importantly, reduces the loss. In addition, air cavity, metal shielding wall, and substrate excavation method also dramatically reduce the loss in substrates. Note that professional material term (FR‐4) material is chosen for the design, therefore, it is low‐cost and more suitable for production application. Finally, a second‐order and a fourth‐order combline BPFs are fabricated and measured to verify the design method. The insertion loss of the second‐order and the fourth‐order filters are only 0.78 and 1.19 dB at the center frequency of 29.2 GHz, respectively. The presented SISL filters using FR‐4 material demonstrate the advantages of low‐loss, low‐cost, and self‐packaging.