Directional coupler with high directivity using metallic cylinders on microstrip line

A directional coupler with high directivity performance using metallic cylinders on the microstrip line is presented. By using two rows of periodic metallic cylinders on a microstrip coupler, the odd-mode phase velocity is slowed down, and thus the directivity can be greatly improved for equal odd- and even-mode phase velocities. The parameters of metalised cylinders, which have an effect on the coupler performance, are investigated. A 12 dB coupler at 2.41 GHz has been designed and measured, providing excellent directivity. Theoretical and experimental results are presented.