In this letter, pseudo-interdigital stepped impedance resonators (PI-SIRs) are used to design the bandpass filter (BPF) with dual-band response. By tuning the impedance ratio (K) and physical length of SIRs, the BPF has good dual-passband performances at 2.4/5.2GHz and high isolation between the two passbands. It is shown that the dual-band BPF has a smaller area and lower insertion loss in comparison of previous works. Good agreement is shown between the full-wave electromagnetic simulation and the measurement

A new quad-band microstrip bandpass filter (BPF) using asymmetric stepped impedance resonators (SIRs) is proposed. The filter only employs two sets of the asymmetric SIRs. One set is designed to operate at the first and third passbands (2.4/5.2 GHz) and the other set is employed at second and fourth passbands (3.5/6.8 GHz). By tuning the impedance and length ratios of the asymmetric SIRs, a multi-band filter can be easily achieved. This study provides a simple and effective method to design a quad-band filter with low insertion loss and compact size. Experimental verification is provided and good agreement has been found between simulation and measurement.

New compact quad-channel diplexer (1.5/2 GHz and 2.4/3.5 GHz) using the coupled stepped impedance resonators (SIRs) is proposed. The quad-channel diplexer is composed of two pairs of coupled SIRs with impedance ratio $({\rm K} > 1)$ and the source-load coupling lines. By tuning the impedance ratio and length ratio $(\alpha)$ of SIRs, the resonant modes can be easily determined so as to implement a two-order bandpass filter with very close dual-passbands. The source-load coupling lines are designed to correspond to the quarter-wavelength at the center frequency of first passband for each output port. The proposed quad-channel diplexer is showing a simple configuration, an effective design method and a small circuit size.