Grating lobe eliminated planar antenna fed by folded oversized-waveguide at 60 Ghz

A double-layered folded oversized-waveguide, was developed for a planer antenna at 60 GHz. This consists of a 2-dimensional parabolic reflector, fed by a high permittivity LSE-NRD guide radiator in the lower layer, and a radiating slotted array, fed by an oversized-waveguide in the upper layer. The upper and lower layers were partitioned by a thick metal plate since permanent magnets for circulators were embedded in the metal plate partition. To effectively introduce a plate wave from the lower layer to the upper layer, a tapered portion was installed in the metal plate partition. To suppress grating lobes in the planar antenna, the radiating slots were spaced by a period of less than a free space wavelength by filling a Teflon material in the upper layer of the oversized-waveguide. Based on the theoretical consideration, the double-layered folded oversized-waveguide with the thick metal plate partition was fabricated and tested at 60 GHz. The levels of the grating lobes were measured to be less than 20 dB compared with that of the main lobe, and hence, successful grating lobe suppression.