PIN Diode Based Variable Directional Coupler

Analysis and design of a novel variable directional coupler using the even-odd mode technique are proposed. In this coupler, the variation of coupling is achieved using a PIN diode, connected to the coupled port of the coupler, while the output is derived from the isolated port. To verify the theory a parallel microstrip line coupler is fabricated on a substrate with r = 3.66, h = 762 µm and tan = 0.006 and measured. The measured results show a variation in the coupling of nearly 20 dB, while at the same time, the change in the direct arm insertion loss is lower than 0.2 dB.