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

• Published in: International journal of electronics and communications 2023-04, Vol.162, p.154580, Article 154580
• Main Authors: Ramkumar, S., Boopathi Rani, R.
• Format: Article
• Language: English
• Subjects: Coupled filter; Hairpin resonator; High selective filter; Microwave filter; Slot line resonator; Wide stopband
• ISSN: 1434-8411; 1618-0399
• DOI: 10.1016/j.aeue.2023.154580

•Formation of a novel coupled filter topology using hairpin and slot line resonators.•Higher order harmonics suppression through middle-shorted hairpin resonators.•Design the layout of the filter to produce high selectivity and wide stopband.•Calculation of coupling matrix and extracting its equivalent coupling coefficients.•Deriving the ABCD and S-parameters and plotting the results theoretically to analyze the filter resonance characteristics. 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.