Constant beamwidth broadband antennas

In a normal horn radiator or aperture type antenna the beamwidth of the main lobe is inversely proportional to the aperture in wavelengths. As frequency is varied the aperture/ wavelength ratio varies in direct proportion, providing a one to one correspondence between frequency and beamwidth. A new type horn radiator called the "pinwall" antenna has been developed which provides an essentially constant beamwidth over a 4 to 1 band instead of the usual 4 to 1 variation in beamwidth that would result from this frequency change. The basic principle behind the pinwall antenna lies in the replacement of the walls of a horn With pins properly spaced to allow the higher frequencies to radiate from a small aperture while constraining the lower frequencies until larger apertures are reached. End-fire radiators were also investigated and dimensions have been obtained for polyrod antennas which produce a constant beamwidth over a 2 to 1 band.