Simple ultra-wideband interdigital bandpass filter with vertical coupling structure

In this paper, simple ultra-wideband interdigital bandpass filter with vertical coupling structure has been successfully demonstrated. This filter provides small size, sharp skirt characteristic by transmission zero, and ultra wideband using vertical coupling structure. From the measurement results, the bandpass filter shows the insertion loss of less than 1.8 dB and the return loss of better than 12 dB with 160% bandwidth at the center frequency of 4.55 GHz. Also, the spurious frequency is improved to be about 13.7 GHz from 8 GHz and the suppression is better than 15 dB. Compared to the configurations of the conventional BPF, a better stopband performance is clearly achieved.