Design of Compact Dual-band Filter Based on Quarter Wavelength SIRs

This paper presents a dual-band bandpass filter based on $\lambda$/4 stepped impedance resonator (SIR), and the principle is introduced in detail. Each passband frequency and bandwidth of the filter can be designed flexibly. In order to verify the effectiveness of this design, a dual-band bandpass filter with center frequencies of 0.85 and 1.65 GHz is designed. The simulation results show that The insertion loss at the center frequency of 0.85 GHz is 0.43 dB and the return loss is 34.2 dB,-3dB fractional bandwidth (FBW) of 16.4 %. The insertion loss at the center frequency of 1.65 GHz is 0.6 dB and the return loss is about 30. SdB, -3dB FBW of 9.1 %. Due to the use of tap feeding and hybrid coupling, the coupling phase changes, and two transmission zeros (TZs) are generated on both sides of the second passband, which greatly increases the out-of-band suppression performance of the filter.