Microstrip even-mode half-wavelength SIR based I-band interdigital bandpass filter

Abstract

In this paper, a new microstrip interdigital even-mode half-wavelength type stepped impedance resonator (SIR) based bandpass filter (BPF) for I-band applications is presented. The bandpass filter characteristic depends on the self-resonant frequency of the interdigital resonated arms. The combination of the interdigital arm structures behaves as an interdigital capacitance coupling between port 1 and port 2. The self generated capacitive and inductive reactances of the interdigital resonators interacted in order to obtain a resonance at 9.4 GHz. The resonant frequency and the bandwidth of the filter are directly optimized as a result of the physical arrangement of the interdigital resonators. The measured insertion loss (S₂₁) and the return loss (S₁₁) are –0.85 dB and –28.0 dB, respectively, at the 9.4 GHz resonant frequency.