A method for low-pass filter designing by commensurate transmission lines

Abstract

It is well known that the complex Richards-Plane is a transformed domain of Laplace-Plane which is obtained under a tangent hyperbolic mapping. Network functions generated in terms of Richards's frequency are periodic in actual frequencies with periodicity of pi. Once a low-pass prototype network function is designed in Richards's domain, then its periodic feature makes the corresponding periodic band-pass network function to appear at the certain bands repetitively in the frequency axis. Depend on the application requirements, designer can choose the interested band among these repetitive bands. In this work, a filter is built with microstrip commensurate transmission lines in GSM operation pass-band (0.8 <= f <= 2.4 GHz) . This network can be used in communication applications which are designed to operate in the range of GHz as well as the application in a microstrip patch antenna. In the proposed design, Simplified Real Frequency Technique (SRFT) is employed in the frequency detection network, and the simulation result of microwave office tool (AWR) confirms the theoretical result obtained by MATLAB.