Synthesis of microwave bandpass filters based on planar quarter-wavelength resonators

• Main Author: Zhang, Songbai
• Other Authors: Law, Choi Look
• Format: Theses and Dissertations
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: http://hdl.handle.net/10356/61527
• Institution: Nanyang Technological University

This Ph.D thesis is dedicated to explicitly synthesize the size-miniaturized and robustly-performed microwave bandpass filters based on planar quarter-wavelength (λ/4) resonators. Unlike the conventional bandpass filters (BPFs) based on J coupling only or K coupling only, λ/4 resonators are necessarily coupled by alternative J and K inverters to realize BPFs. The exemplified filters in this thesis not only include single-band bandpass filters (SB-BPFs) with all-pole Chebyshev and quadruplet frequency responses, but also the dual-band bandpass filters (DB-BPFs) and a tri-band bandpass filter (TB-BPF) based on the λ/4 stepped impedance resonators (SIRs). According to the literature survey on the classical filter synthesis, the conventional even-order lowpass Chebyshev ladder network features the unequal input/output (I/O) impedances. Hence, a novel even-order Chebyshev lowpass prototype is presented here to achieve the equal I/O terminations. This proposed Chebyshev prototype is then deployed to synthesize BPFs based on λ/4 resonators. The equivalent network transformation from the conventional J or K immittance bandpass prototypes to the ones based on λ/4 resonators coupled by alternative J and K inverters is performed and discussed in details. Following that, an explicit full-wave dimension extraction method is then proposed to rigorously extract the filter’s physical dimensions, whose robustness is demonstrated by synthesizing series of SB-BPFs with either all-pole Chebyshev frequency responses or the quadruplet frequency responses with analytical finite transmission zeros. Furthermore, the bandpass filter prototype with planar λ/4 resonators and alternative J and K inverters is extended for the DB-BPF application. Since the K inverter’s value of quasi-lumped metallic through via increases monotonically with frequency, the dimensions of concerned λ/4 SIRs are analytically determined to compensate for the dual-band values of K inverters. With the dual-band J couplings and the newly-proposed dual-band external couplings structures, a class of compact and robustly-performed DB-BPFs are proposed and designed. Besides the DB-BPFs based on dual-band λ/4 SIRs, the novel split-type DB-BPF based on the uniform λ/4 resonators is also presented, which is more suitable for the DB-BPF application with closely proximate dual passbands. Lastly, we also exemplify a TB-BPF design. Experimental results successfully justify our filter synthesis methodology in this thesis.