A large planar 39-GHz antenna array of waveguide-fed horns

A planar antenna in which box horns are used as radiating elements is described. The feed network is built by connecting rectangular waveguides with T-junctions. The matching of the T-junctions is improved by using rounded splitters and matching pins in the junctions. The radiating element has been designed to cancel out the grating lobe. The grating lobe is due to an element spacing larger than one wavelength. The highest sidelobes are at least 31 dB below the main beam in the H-plane and 16 dB in the E-plane. A gain of 37 dBi has been achieved at 39.2 GHz. These results demonstrate the feasibility of this antenna for applications requiring high gain at millimeter wavelengths