Fabrication of a novel diplexer using folded open-loop ring resonators and microstrip lines

A simple and novel low-loss diplexer with two folded Open-Loop Ring Resonators (OLRRs) that couple three microstrip lines is proposed. The first passband and second passband of the designed diplexer could be easily and accurately shifted to a desired frequency and construct the bandpass filters by adjusting the physical dimensions of the OLRRs. These results suggested that the proposed diplexer had the frequency-adjustable characteristics. The longer OLRR is placed between the upper and middle microstrip lines to generate a 2.4 GHz resonant frequency and the shorter OLRR is placed between the middle and lower microstrip lines to generate a 5.2 GHz resonant frequency. By adjusting the positions of the two OLRRs, the resonant frequencies can be tuned.