A Compact and High-Isolated Multiresonator-Coupled Diplexer

A compact and high-isolated microstrip diplexer by using multiple-coupled resonators with separated electric and magnetic coupling paths and dual-mode characteristic has been presented. Multiple transmission zeros have been obtained, and some of them can be controlled by the electric and the magnetic couplings. The diplexer has been fabricated and measured, and the design has been demonstrated. The developed diplexer has a measured passband insertion loss of not more than 2.15 dB, a measured isolation of more than 38 dB, and a compact circuit size of
$0.66\lambda _{\mathrm{g}} \times 0.15\lambda _{\mathrm{g}}$
at the lower frequency band.