Wideband Microstrip Ring Resonator Bandpass Filters Under Multiple Resonances

• Published in: IEEE transactions on microwave theory and techniques Vol. 55; no. 10; pp. 2176 - 2182
• Main Authors: Sheng Sun, Sheng Sun, Lei Zhu, Lei Zhu
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.10.2007; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Asymmetry; Band pass filters; Bandpass filters; Circuit properties; Couplings; Dielectric, amorphous and glass solid devices; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Exact sciences and technology; Filtering; Filtration; Frequency filters; Microstrip filters; Microstrip resonators; Microstrip ring resonator; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; multiple resonant modes; Optical ring resonators; Oscillators, resonators, synthetizers; parallel-coupled line; Passband; Ports; Rejection; Resonance; Resonator filters; Resonators; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Shape; Wideband; wideband bandpass filter; Performance evaluation; Microstrip filters; Lumped parameter circuit; Coupled line; Wide band; multiple resonant modes; Two-port networks; Band pass filter; Capacitive coupling; Open circuit; Wide band circuit; Filtering; Resonator filters; Stub line; Microstrip resonator; Mode filter; Ring resonator; First order; wideband bandpass filter; Transmission line theory; parallel-coupled line; Passband; Capacitor; Microstrip ring resonator; Interdigital configuration
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2007.906510

A new class of wideband microstrip bandpass filters is proposed under multiple resonances of an asymmetric ring resonator. Two capacitive coupling elements are placed at two perpendicular positions of a squared ring, whereas a pair of open-circuited stubs is formed in the symmetrical plane of these two excited ports similar to a dual-mode ring filter in shape. By stretching the paired stubs close to one-eighth of a wavelength, the first two even-order resonances move down to be quasi-equally located at two sides of the first odd-order resonance, thus forming a triple-resonance ring resonator. As interdigital coupled lines are installed at two ports instead of lumped capacitors, two extra resonances can be moved into passband, thereby making up a quintuple-resonance ring resonator. To provide an insight into their operating mechanism, these ring resonators are characterized in terms of transmission line theory. Afterwards, various wideband microstrip ring resonator bandpass filters with one or two asymmetric ring resonators are optimally designed and fabricated. Simulated results are confirmed via experiment, showing good wideband filtering performance with widened/deepened upper stopband and sharpened rejection skirts outside the wide passband.