A compact eight-channel microstrip quadruplexer using quad mode stub-load resonators

A new microstrip eight-channel quadruplexer with compact-size and high-isolation is proposed in this paper. The proposed eight-channel quadruplexer is formed by four dual-band bandpass filters (BPFs) based on the quad-mode stub-load resonators. By adjusting the geometric parameters of a single quad-mode stub-load resonator, its first four resonant frequencies can be well controlled and, thus, it can be utilized to implement a second-order dual-band filter when these resonant frequencies are properly allocated. For the demonstration, an eight-channel quadruplexer has been designed and fabricated with microstrip technology. The size of the fabricated quadruplexer is about 0.18 λg by 0.49 λg. As a result, the measured results are in good agreement with the simulated predictions, showing that better than 30 dB output isolation is achieved.