Design of enhanced stopband bandpass filter with mixed electric and magnetic coupling

A new compact bandpass filter(BPF) with improved out-of-band performance is presented in this paper. The proposed BPF consists of two non-adjacent stepped impedance resonators (SIRs), which shared a common grounded via-hole. To improve the stopband characteristics, a π type capacitive circuit is introduced in the filter. The location of the transmission zeros can be controlled by adjusting the strength of the mixed electric and magnetic (EM) coupling. Simulated results show that good performance of proposed BPF at 1.38GHz has been achieved.