COMPACT BANDPASS FILTER WITH MIXED ELECTRIC AND MAGNETIC (EM) COUPLING

A compact wide-band bandpass filter (BPF) with high frequency selectivity using stepped impedance resonators (SIRs) is presented in this paper. The proposed BPF consists of four SIRs, which share a common grounded via-hole. To improve the frequency selectivity, multiple transmission zeros (TZs) are employed in the stopband by mixed electric/magnetic (EM) coupling. The novel filter with 32.2% fractional bandwidth (FBW) has been designed and fabricated to verify the validity of the proposed method. Measured results are in good agreement with the electromagnetic simulation. The measured results show three finite transmission zeros in the stopband, located at 2.47 GHz, 5.26 GHz, 9.39 GHz, respectively. The circuit size of proposed BPF only occupies 3:10 × 13:30mm2.