Crenellated terminations—Pill box type aerials

The pill box antenna, in common with waveguide apertures and shallow horns with a small width in terms of wavelength in the direction of the E vector, on many occasions proves inconvenient in practical use due to the traveling waves set up on the outside of the radiator. Crenellations are described which substantially cancel this backward radiation, and provide 3 dB increase in forward gain together with a large reduction of standing waves within the pill box.