Compact high-selective wide-stopband coupled bandpass filter using middle-shorted hairpin-resonators

Abstract

In this letter, a novel compact highly selective coupled bandpass filter (BPF) with sharp roll-off and wide stopband with excellent attenuation is proposed. This BPF is designed using two middle-shorted hairpin-resonators and a slot line resonator. The coupling matrix is calculated theoretically as per the specifications. The coupling coefficients between the resonators are computed by using the full-wave simulator HFSS to properly select the coupling gap between the resonators. The ABCD and S-parameters of the proposed design are computed, and the S-parameters are plotted theoretically. The designed filter is fabricated and tested. Good agreement is found between simulation and measurement. The proposed filter has excellent measured characteristics, including an insertion loss of 1.2 dB, a return loss better than −20 dB, high band edge attenuation of 60 dB, three Transmission Zeros (TZs), and a wide stopband rejection of greater than 30 dB up to 3f0 where f0 is the center frequency of the BPF. The proposed filter can be used for WLAN applications.