Microstrip Coupler with High Isolation
Microstrip couplers are widely used in microwave applications such as antenna feeds, balanced mixers, modulators, phase shifters and so on. But, they suffer from poor isolation, due to the inequality between the odd and even mode phase velocities. A method to improve the isolation of the microstrip coupler is presented. The pattern of the coupler is modified for phase velocity compensation which results in high isolation. Using this procedure, a 15dB coupler is designed and fabricated at 0.9GHz. A high isolation of 63.3dB is measured. The validity of the design concept is verified by simulations and measurements.