Wide-stopband microstrip quadruplexer using asymmetric stepped-impedance resonators

A microstrip quadruplexer with a wide stopband is presented in this paper. The quadruplexer consists of asymmetric stepped-impedance resonators (SIRs) and a distributed common feeding line. In order to increase the stopband bandwidth, the higher order resonant frequencies of the asymmetric SIRs are staggered by properly selecting impedance ratio K and length ratio. Thus, a wide upper stopband performance can be achieved. The first, second, third, and forth channels of the quadruplexer are designed at 1.5, 1.8, 2.1, and 2.4 GHz (denoted by f₁, f₂, f₃, and f₄). For the upper stopband performance, the rejection level is greater than 20 dB up to 11.4 f₁ (17.1 GHz).