Rotary Joint Perpendicularly Fed by a Substrate Integrated Waveguide Feeder

Two rotary joints perpendicularly fed by the substrate integrated waveguide (SIW) feeder are presented in this paper. The planar SIW feeder excites the circular waveguide with the desired rotational symmetric mode through a circular slot, whose effect can be modeled through a horizontal magnetic current on the top surface of the SIW. First, a single-layer SIW feeder is designed in the rotary joint with simple configuration. After that, a dual-layer SIW feeder is proposed to improve the performance of the single-layer version, especially for the bandwidth. Both of them have two controllable transmission poles, which can be used to optimize performance. After introducing the design principle and process, two rotary joints perpendicularly fed by different SIW feeders are fabricated and measured. For the dual-layer feeder rotary joint, it is able to operate from 11.1 to 12.4 GHz. Within an 11.1% relative bandwidth, its insertion loss is less than 1.21 dB and return loss is better than 10.85 dB when being rotated at different angles.