General synthesis method for symmetrical even-order Chebyshev bandpass filter

Abstract

This paper proposes a general synthesis method for the even-order Chebyshev bandpass filter with equal I/O port impedances. It is prevalently accepted that the even-order Chebyshev filter has unequal I/O terminations due to impedance mismatch at D.C. in its lowpass prototype. In this paper, two symmetrical properties are firstly found among the elements of even-order Chebyshev lowpass ladder network. A symmetrical even-order Chebyshev lowpass network with equal terminations are then proposed based on both properties, which tackles the impedance mismatch with the inverters rather than the load conductance/resistance. Subsequently, a 4th-order Chebyshev bandpass filter based on λ/2 microstrip-line resonators centering at 2.4 GHz with a fractional bandwidth of 10.0% are synthesized and fabricated, the measured results provide strong verification for the proposed synthesis method.