A low-cost microwave rotary joint

A simple and cheap coaxial microwave rotary joint covering frequencies from 1 to 21 GHz is described. Measured typical insertion loss is 0.7 dB, return loss stays better than 10 dB and the rotating torque requirement is 26 mNm. Maximum variation of attenuation as a function of rotating angle is 0.5 dB. Operation up to 37 GHz has been tried with loss values around 2 dB, typical.