A Novel Filtering Balun Implemented in Substrate Integrated Waveguide Technology

This paper presents a novel filtering balun implemented in substrate integrated waveguide (SIW) technology using modified coupling matrix. The filtering response is achieved using four SIW cavity resonators with iris openings. The balanced output ports (port 2 and port 3) are placed opposite to each other in different layers so as to achieve equal power division and out-of-phase characteristics when the signal is propagating from port 1. To verify the proposed design, SIW filtering balun is simulated at center frequency of 3.5 GHz with 150 MHz bandwidth. The simulated return loss obtained is 19 dB over the entire band and the peak insertion loss is 4.5 dB. As expected, there are no amplitude and phase imbalances in the simulated results. In addition, the design methodology is scalable to realize higher-order filtering response.