High isolation diplexer for rf circuits using loop resonators

A high isolation Diplexer with Pentagonal Open Loop Resonators (P-OLR) is presented in this paper. The Diplexer contains two resonators providing pass bands in the desired frequency, thus attaining significant size reduction. The P-OLR offers several design freedoms, such as the pass band frequency can be adjusted by properly tuning its geometrical parameters and its bandwidth can be controlled through changing the coupling coefficients between the T-shaped feed and the resonator. To verify the designed method a P-OLR diplexer operating at the Wi-Fi bands is successfully designed and fabricated on FR4 epoxy. The maximum insertion loss of two pass bands is 1.5 dB and the isolation between channels at the pass bands higher than 25 dB.