Compact and high-performance bandpass filter and diplexer based on SCMRC-loaded SIR

Bandpass filter (BPF) and diplexer, which are required to be compact size and high performance, are widely used in modern wireless communication systems. In this article, novel BPF and diplexer are designed using the proposed resonator called spiral compact microstrip resonator cell (SCMRC)-loaded stepped-impedance resonator (SIR). The SCMRC-loaded SIR is proposed using the slow-wave structure SCMRC to replace the low-impedance section of the conventional SIR. Compared with the conventional SIR, the new SCMRC-loaded SIR has a compacter size and can generate a transmission zero above its fundamental resonant frequency. As examples, a BPF with the central frequency at f ₀ = 1 GHz and a diplexer operating at 0.9/1.57 GHz are designed and fabricated. The fabricated BPF occupies a compact size of 0.07 λ ₀ × 0.035 λ ₀ and has a -60 dB rejection level wide stopband from 1.2 f ₀ to 3.8 f ₀. The fabricated diplexer occupies a compact size of 0.076 λ ₀ × 0.128 λ ₀ and has an up to -50 dB output isolation. Good agreement can be observed between the simulations and the measurements.