A Low Cross-Polarization Slotted Ridged SIW Array Antenna Design With Mutual Coupling Considerations

A novel shunt longitudinal slot planar array antenna based on a ridged substrate integrated waveguide (RSIW) with a good cross polarization and isolation is designed and fabricated. The slots in the proposed structure are placed on the centerline of the broad wall of the substrate integrated waveguide (SIW), in order to reduce cross polarization. Also, the asymmetric field distributions on both sides of each slot, which are required for making radiation possible, are realized through using ridges close to the narrow walls of the SIW. The admittance of a single slot in the proposed structure is obtained regarding the different values of the main parameters of the structure. An eight-element longitudinal slot array antenna on the broad wall of the RSIW is designed based on Elliot's design procedure. In this design, internal and external mutual coupling effects are taken into account through calculating the active admittance for each slot of the array. A 2-D graph is presented which contains the real and imaginary parts of the equivalent admittance of a slot based on the changes in the widths of the ridges and length of the slot. Using this graph, the widths of the ridges and length of the slot can be revised in a way that the mutual coupling effect is taken into account. Since the array antenna is composed of collinear elements, it demonstrates a better cross polarization and isolation in comparison with conventional slot array antennas. Simulation results show good agreement with measurement results of the fabricated proposed antenna.