Bandpass Filters Designed by Transmission Zero Resonator Pairs With Proximity Coupling

• Published in: IEEE transactions on microwave theory and techniques Vol. 65; no. 11; pp. 4103 - 4110
• Main Authors: Xue, Quan, Jin, Jun Ye
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.11.2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bandpass filter; Bandpass filters; Coupling; Couplings; Cutoff frequency; Design; Electromagnetic wave filters; Filter design (mathematics); Filtering theory; Microstrip; Microstrip transmission lines; microwave filter; Passband; Poles and zeros; Rectangular waveguides; Resonant frequencies; Resonant frequency; Resonators; Selectivity; transmission zero resonator pairs (TZRPs); transmission zeroes; waveguide filter
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2017.2697878

The concept of transmission zero resonator pair (TZRP) is used in this paper. Based on this TZRP, a new method to induce a passband is demonstrated, by which different types of bandpass filters can be designed. The proposed TZRP is structured by a pair of resonators with different resonant frequencies, which lead not only to two transmission zeroes, but also to a transmission pole between them. Passband filters can then be built by designing the proximity coupling between the TZRPs, as the TZRP works as a basic resonant element. The passband of these filters can be flexibly controlled by the resonators of TZRPs, which determine the locations of the transmission zeroes and poles. By carefully allocating the transmission zeroes, high selectivity and large out-of-band rejection can be realized. This design method is applied to design filters in two different transmission media, namely, microstrip line and rectangular waveguide. Simulated and measured results demonstrate the effectiveness of this new approach of bandpass filter design. The designed filters have the properties of small size, easy fabrication, low cost, and low loss.