Design of the Air-Filled Coaxial Diplexer

This paper presents an air-filled coaxial diplexer. A T-shaped structure is designed to connect two bandpass filter (BPF) through a common port. The full-wave simulation and optimization of the diplexer is implemented through CST based on the finite time domain integration method. The two passband fractional bandwidths are 12.75% and 7.7% respectively.