A stacked dual-mode bandpass filter with circular cavity

In this paper, a bandpass filter based on two stacked dual-mode circular cavity (DMCC) is designed for the fifth-generation (5G) mobile communications system. In each single cavity there are two resonant modes, which can generate and control two transmission zeroes at specific frequencies. Through a coupling iris the two stacked single-cavities are connected together, and can control four transmission zeroes, which expands the 3dB fractional bandwidth to 11.4% at the center frequency of 3.5GHz. The stacked filter has the advantages of low cost, compact size, high frequency selectivity, and very low insertion loss.