Balanced Quad-Band Bandpass Filter With Controllable Frequencies and Bandwidths

• Published in: IEEE access Vol. 7; pp. 140470 - 140477
• Main Authors: Wei, Feng, Zhang, Chi-Yuan, Yue, Hao-Jie, Shi, Xiao-Wei
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Asymmetric short stub-loaded resonators (ASSLRs); balanced BPF; Band-pass filters; Bandpass filters; Couplings; Frequency control; Microstrip; microstrip/slotline (MS) transition structures; Passband; quad-band; Resonant frequency; Resonators; Selectivity; Stability
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2019.2943704

A balanced microstrip quad-band bandpass filter (BPF) employing balanced microstrip/slotline (MS) transition structures and two pairs of folded asymmetric short stub-loaded resonators (ASSLRs) is presented in this paper. The center frequencies of the four differential-mode (DM) passbands can be controlled by changing the electrical length ratio of each ASSLR. Meanwhile, the fractional bandwidths (FBWs) can be adjusted by controlling the coupling gaps between the resonators and interdigital coupled line. High selectivity of the four DM passbands is achieved by introducing eight transmission zeros (TZs). Moreover, the DM passbands are independent from the common-mode (CM) responses, which significantly simplifies the design procedure. In order to validate the design strategies, a balanced quad-band BPF centered at 2.54/ 3.46/ 4.5/ 5.2 GHz was fabricated and a good agreement between the simulated and measured results is observed.