Design of a dual-ring microstrip antenna excited by an inclined slot on a narrow wall of the rectangular waveguide for a 45-degree linearly-polarized planar array

This paper presents design of a dual-ring microstrip antenna (MSA) fed by an inclined slot on a narrow wall of the rectangular waveguide for a 45-degree linearly-polarized planar array. In order to suppress grating lobes radiated from a slot array arranged at a spacing of one guided wavelength of the waveguide, it is proposed to arrange dual-ring MSAs with a circumference of approximately 5 wavelengths on the slot array with a dielectric substrate. In this paper, a dual-ring parallelogram MSA excited by an inclined slot on a narrow wall of the waveguide is designed as an element of a 45-degree linearly-polarized planar array by using ANSYS HFSS. The design frequency is 11.2 GHz and an X-band standard waveguide is used. It is confirmed by the simulation that 45-degree linearly polarized radiation as well as a sharp main beam in the waveguide axis plane for grating lobe suppression can be obtained by the designed MSA at the design frequency.