Synthesis design of dual-path coupled line circular ring resonator filter with tunable characteristic impedances and transmission zeros

• Published in: IET Microwaves, Antennas and Propagation
• Main Author: Nordin S.A.; Hairuddin M.A.; Khirul Ashar N.D.; Khan Z.I.
• Format: Article
• Language: English
• Published: John Wiley and Sons Inc 2021
• Online Access: https://www.scopus.com/inward/record.uri?eid=2-s2.0-85112035158&doi=10.1049%2fmia2.12132&partnerID=40&md5=b6122a19ed9848c170ded93935a0e125

A dual-path coupled-line circular ring resonator filter synthesis is presented. The topology comprises identical coupled lines in series duplicated to form dual-path coupled-line interconnections. A bandpass response of nth order equal to (n/2) + 1, corresponds to controllable transmission zeros (TZs) found on both sides of the passband by varying the values of the even- and odd-mode impedances of the coupled lines, denoted Zoe and Zoo, respectively. Concerning the efficiency of controllable electrical characteristics of the resonator filter, such as in-band matching level, high selective response, and wide bandwidth, and fixing the position of the TZ frequencies, the proposed method using asymmetrical quarter-wavelength coupled lines in a circular ring resonator filter is superior to existing methods. Ultimately, the proposed bandpass filter is implemented on contrast dielectric substrate FR-4 and Taconic TRF-45 substrates using a planar form of microstrip technology to verify the synthesis equation. The measurement results indicate that the filter achieved more than 40% fractional bandwidth with excellent in-band matching levels and a controllable filter order. Both measurement and simulation results are in good agreement regarding return and insertion loss values, thus validating the proposed designs. © 2021 The Authors. IET Microwaves, Antennas & Propagation published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.