Direct Synthesis of General Chebyshev Bandpass Filters in the Bandpass Domain

Abstract

Conventional synthesis technique for general Chebyshev bandpass filters usually derives filtering polynomials from general Chebyshev filtering function. Then, lowpass prototypes or coupling matrices in the lowpass domain are derived and are transformed into the bandpass domain for practical application. Unfortunately, it has some disadvantages such as incapability to synthesize filters with asymmetric frequency response and narrow-band limitation. In this paper, two techniques to directly synthesize filters in the bandpass domain are discussed, i.e., the direct technique based on local mapping and the direct technique based on global mapping. The real-coefficient filtering polynomials constituting scattering parameters will be derived directly in the bandpass domain, and then used to constitute impedance or admittance parameters for network realization. In this paper, one approach to synthesize bandpass filters in terms of coupled resonators is discussed. Several examples are presented for demonstration. The direct techniques discussed in this paper are flexible so that general Chebyshev bandpass filters with arbitrarily placed transmission zeros might be synthesized.