DESIGN OF EVEN-ORDER SYMMETRIC BANDPASS FILTER WITH CHEBYSHEV RESPONSE

Abstract

This paper proposes a method to design an even-order symmetric bandpass fllter with Chebyshev response. The alternative J inverters and ‚=4 short-ended resonators are used in the fllter design. It is well known that a conventional even-order Chebyshev bandpass fllter prototype can be designed by using Jinverters. However, to achieve the Chebyshev response, a problem is that the output admittance YL is unequal to the input admittance Y0 since normalized gn+1 is not equal to the g0. Thus, for the symmetrical structure, an additional impedance transform can be installed at the output port to solve this problem, thus the network of even-order symmetric bandpass fllter with a Chebyshev response should be modifled with new J-inverters. In this work, all J-inverters of the symmetric bandpass fllter with Chebyshev response are extracted and described as curves to determine the circuit dimensions of the proposed structure. Two even-order Chebyshev bandpass fllters with the second- and fourth-order are designed with the proposed method as its application examples. Finally, the fourth- order fllter is fabricated and measured at center frequency of 2.5GHz with the fractional bandwidth 25%. The measured result is in good agreement with the simulated one.