A Compact and Broadband Balun Based on Multilayer SIW

A compact broadband balun based on a new planar wideband power divider circuit is presented in this work, which makes use of the substrate integrated waveguide (SIW) technique and multilayer printed circuit board (PCB) process. A broadband 180° reverse-phase characteristic between the two output ports can be easily achieved by the middle metal-ground of the SIW power divider. An elliptic coupling slot is utilized for this multilayer SIW power divider to realize a broad passband. The concept is validated by simulation and measurement. The measured results suggest that a 10 dB return loss at the input can easily be achieved, across a 50.3% relative bandwidth from 11.3 to 18.9 GHz. The measured amplitude and 180° phase imbalance between the two outputs are within 0.35 dB and 1.9°, respectively.