A large planar antenna consisting of an array of waveguide fed horns

A planar array antenna in which box horns are used as radiating elements is proposed. The antenna consists of two parts, one containing the feed network and the other 256 radiating elements. The radiation pattern of the single radiating element is specially designed to cancel out the sidelobes of the array due to the element spacing larger than one wavelength. 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. A planar antenna for the frequency range 37.0-39.5 GHz has been designed. The measured radiation pattern of a prototype antenna is extremely directive in both the E-and H-planes and a gain of 37 dBi at 39.2 GHz has been achieved. The highest sidelobes are at least 31 dB below the main beam in the H-plane and 15 dB in the E-plane.