Using Via Stubs in Periodic Structures for Microwave Filter Design

This paper presents a novel form of microwave filter construction using vias (plated through holes) available in generic printed circuit boards as the main building block. It is demonstrated that for a certain arrangement of vias, the resonant behavior of via stubs can be used to create a low- or a high-pass filter using open- or short-circuited vias, respectively. These stubs are periodically cascaded, resembling an analogous implementation using transmission-line stub filters. It will be shown that such a via filter structure can achieve insertion loss lower than 0.1 dB and return loss of about -60 dB in the passband at GHz frequencies. Measurements, full-wave, and physics-based simulations are presented to verify this novel filter concept and to provide design guidelines in the frequency range from 1 to 20 GHz.