A novel 0dB microstrip coupler with double-ring

In order to solve crossover of lines in MMIC (Monolithic Microwave Integrated Circuits), a novel microstrip coupler has been presented. With a double-ring structure, the presented coupler achieves high isolation between adjacent ports. The size of coupler has been reduced by using an arc impedance transformer; Parameters influencing resonance loop and impedance matching of the coupler have been analyzed and the equations of theses parameters have been derived. Simulation, fabrication and measurement for the coupler have been done. Simulation of the relative bandwidth of reflectance, insertion loss and isolation is 18.61% (S11<;-10dB), 7.31% (S12>-1dB) and 4.99% (S13<;-15dB) respectively. Correspondingly measurement results is 17.94%,8.04% and 4.80%. Simulation and measurement results agree very well, which confirms the validity of the design.