A Broadband Magnetic Coupling Microstrip to Waveguide Transition Using Complementary Split Ring Resonators

A novel broadband microstrip to waveguide transition is proposed in this paper. A microstrip circuit is inserted into a waveguide along the axis of the broadside wall, and the referred waveguide is WR-90 standardized rectangular waveguide. The microstrip circuit consists of a pair of symmetric step-like patches, a microstrip probe, and a metal ground plane. The transition has a smaller size as it is end-inserted. Meanwhile, the traditionally stepped metal ridge in the waveguide is replaced with bistratal symmetric patches, integrated design of patches, and microstrip probe. Therefore, the welding loss and structural instability have been avoided. Complementary split ring resonators are loaded in the patches to broaden the bandwidth and increase efficiency. Measured results show that the proposed microstrip to waveguide transition achieves a -15 dB return loss with the bandwidth of 8.65-12.33 GHz, and its insertion loss is better 0.5 dB over the band of 8.13-12.13 GHz. Furthermore, this design features lightweight, low cost, and simple processing methods.