Design of microstrip bandpass filters with multiorder spurious-mode suppression

• Published in: IEEE transactions on microwave theory and techniques Vol. 53; no. 12; pp. 3788 - 3793
• Main Authors: CHEN, Chi-Feng, HUANG, Ting-Yi, WU, Ruey-Beei
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.12.2005; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Band pass filters; Bandpass filters; Chebyshev approximation; Circuit properties; Coupling coefficient; Design engineering; Design methodology; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; elliptic-type bandpass filter; Exact sciences and technology; Frequency filters; Guidelines; Impedance; microstrip filter; Microstrip filters; Microstrip resonators; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Microwave filters; Microwaves; Oscillators, resonators, synthetizers; Passband; Resonant frequency; Resonator filters; Resonators; Retarding; Simulation; stepped-impedance resonator (SIR); Microstrip filters; Resonator; elliptic-type bandpass filter; Multivariable control; Stepped impedance device; Chebyshev filter; Knowledge base; Spurious signal; Coupling coefficient; Elliptic filter; Resonance frequency; Parallel connection; Band pass filter; microstrip filter; Impedance; stepped-impedance resonator (SIR); Fundamental frequency
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2005.859869

This paper proposes a bandpass filter design method for suppressing spurious responses in the stopband by choosing the constitutive resonators with the same fundamental frequency, but staggered higher order resonant frequencies. The design concept is demonstrated by a four-pole parallel-coupled Chebyshev bandpass filter and a compact four-pole cross-coupled elliptic-type bandpass filter. Each filter is composed of four different stepped-impedance resonators (SIRs) for which a general design guideline has been provided in order to have the same fundamental frequency and different spurious frequencies by proper adjusting the impedance and length ratios of the SIR. Being based on knowledge of the coupling coefficients and following the traditional design procedure, the resultant filter structures are simple and easy to synthesize. The measured results are in good agreement with the simulated predictions, showing that better than -30-dB rejection levels in the stopband up to 5.4f/sub 0/ and 8.2f/sub 0/ are achieved by the Chebyshev and quasi-elliptic filters, respectively.