A widely-tunable substrate-integrated balun filter

• Published in: 2017 IEEE MTT-S International Microwave Symposium (IMS) pp. 274 - 277
• Main Authors: Hickle, Mark D., Peroulis, Dimitrios
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01-06-2017
• Subjects: Band-pass filters; Cavity resonators; Couplings; Filters; microwave filters; passive filters; Resonator filters; tunable filters; tunable resonators; Tuning
• DOI: 10.1109/MWSYM.2017.8059095

A novel differential coupling structure for tunable evanescent-mode cavity resonators is presented in this paper. The coupling structure is very simple and compact, and presents no design or fabrication challenges relative to a comparable single-ended coupling structure. This new coupling structure is used to realize a high-performance 3-pole tunable balun bandpass filter, which integrates the functionalities of a tunable bandpass filter and a balanced-to-unbalanced transformer (balun). The filter tunes from 3.2 to 6.1 GHz, and has a nominally 2.4% 3-dB fractional bandwidth. It demonstrates state-of-the-art measured amplitude and phase balance among tunable balun filters, with less than 0.2 dB and 0.9 o of in-band amplitude and phase imbalance across its entire tuning range.