In this paper, a novel directional filter (DF) is proposed and implemented using substrate integrated waveguide (SIW) technology which exhibits the advantages of compact size and simple structure. The proposed DF is realized by two half mode substrate integrated waveguides (HMSIWs) and two substrate integrated circular cavity (SICC) resonators operating in the TM110 degenerate modes in which an aperture is utilized to realize the coupling between HMSIWs and SICCs. Two slotlines with appropriate dimensions, etched on the top and bottom planes, are utilized in order to control coupling strength between two cascaded SICC resonators. The proposed two-circular cavity SIW DF at 12.3 GHz is designed and fabricated with a normal printed circuit board process. Measured and simulated results indicate that the DF has a 3.25% bandwidth, and the return loss as well as isolation are better than 10.5 and 15 dB, respectively.

Design and realisation of a compact power divider based on half mode substrate integrated waveguide (HMSIW) with an arbitrary power dividing ratio is presented. This design consists of a substrate integrated waveguide (SIW) transition, two bisected HMSIW transitions by a gap, an SIW-to-microstrip transition, and two microstrip feed lines. In addition, a resistor is attached between two HMSIW transitions. To adjust the power division ratio, four parameters are introduced. Furthermore, four graphs are plotted using a three-dimensional electronmagnetic (3D EM) simulator to graphically determine the introduced parameters. In this study, three circuits with power division ratios of 1:1, 1:4, and 1:8 are simulated using the 3D EM simulator and fabricated on a Rogers RO4003C substrate. The results show a good agreement between the simulated and measured results. The measured results display these circuits (1:1, 1:4, and 1:8) have the bandwidths of 70, 36, and 40%, respectively. Moreover, the proposed structures (1:1, 1:4, and 1:8) are compact and their overall sizes are $1.13 \times 1.04\lambda _g^2 $, $0.96 \times 0.91\lambda _g^2 $, and $0.81 \times 0.78\lambda _g^2 $, respectively. These structures have the advantages of the compactness in size, wide bandwidth, high power division ratio (from 1:1 to 1:16), and compatibility with planar circuits.