Novel Wideband Differential Bandpass Filters Based on T-Shaped Structure

• Published in: IEEE transactions on microwave theory and techniques Vol. 60; no. 6; pp. 1560 - 1568
• Main Authors: Feng, Wenjie, Che, Wenquan
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-06-2012; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Band pass filters; Bandpass filter; Bandpass filters; Bandwidth; Circuit properties; Couplings; Cross coupling; differential/common mode; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Equivalent circuits; Exact sciences and technology; fractional bandwidth; Frequency filters; Impedance; Microwaves; Noise levels; Oscillators, resonators, synthetizers; Passband; Resonant frequency; Resonators; Selectivity; T-shaped structure; Wideband; Resonator; Wide band circuit; Prototype; differential/common mode; Compact design; Selectivity; Transmission zero; fractional bandwidth; Harmonics suppression; Bandpass filter; Wide band; wideband; Insertion loss; T-shaped structure; Band pass filter; Passband; T shape
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2012.2188538

Two novel wideband differential bandpass filters based on a T-shaped structure are proposed in this paper. Broad passband and wideband harmonic suppression for the differential/common mode can be easily achieved for the wideband differential filter without cross coupling, due to the controlled resonator frequencies of the shorted/open T-shaped structure. In addition, another more compact differential filter using cross coupling is proposed with two transmission zeros close to the passband to improve the selectivity for the differential mode. To verify the presented concept, two prototypes (ε r = 2.65, h = 0.5 mm) with 3-dB fractional bandwidth of 70% and 70.7% for the differential mode and insertion loss greater than 13.5 dB for common mode (0-19 GHz) are designed and fabricated. Good agreement can be observed between measured results and theoretical expectations.