Design of SIR Coupled Resonator Bandpass Filter Based on LTCC

This paper describes a 6th-order coupled bandpass filter based on the SIR structure. In order to reduce the size of the filter and improve its performance, LTCC technology is adopted. The overall dimensions are 6.8mm×4.2mm×1.5mm. Following the basic principles of SIR coupled resonance, cross-coupling is introduced between input and output resonant stages to generate transmission zeros, achieving high out-of-band suppression. The HFSS software is utilized for modeling, simulation, and optimization of key parameters. The filter operates between 3.15GHz and 3.45GHz with a center frequency of 3.3GHz, exhibiting return loss better than 10dB. Multiple transmission zeros are generated outside the passband, achieving attenuation of 34dB at low out-of-band frequencies of 120MHz and 32dB at high out-of-band frequencies of 120MHz. Thus, the filter demonstrates excellent frequency selectivity.