Design of miniaturized dielectric duplexer with attenuation poles

Abstract

AbstractA design method is conceived for a miniaturized antenna duplexer with attenuation poles. Its effect is indicated by using it as an antenna duplexer for the 800‐MHz portable telephone. The transmitting filter has a band‐rejection filter characteristic of an elliptic function type while the receiving filter has a Chebyshev bandpass filter with attenuation poles. Previously, the design of these filters has been carried out by an optimum design using an iterative approximation from an initial design value. Hence, a large amount of computation time was required.This paper proposes a design method without an iterative approximation. In the transmission filter, resonators with a low characteristic impedance are used. In the conventional band‐rejection filter design of an elliptic function type, the linearity of the reactance slope of the resonators is degraded and the insertion loss near the passband edge increases. A method of compensating for this increase is presented. In the receiving filter, the design equation for the conventional Chebyshev characteristic was modified. It is shown that a bandpass filter characteristic with attenuation poles can easily be designed. A branching circuit is added to these filters, and an antenna duplexer is constructed with a minimum number of components by the circuit transformation. The computed values of the filter characteristic agreed well with the actual example. In comparison with the optimization method based on the iterative approximation, the amount of computation for the design was about one‐twentieth.