Highly contoured beam antennas for 21 ghz‐band ldr hub stations

Abstract

AbstractWith a view to applications of the 21‐GHz LDR (local distribution radio) system to point‐to‐multipoint systems, a hub station antenna was developed which produces an improved cosecant square beam in the vertical plane and the fan beam in the horizontal plane. The antenna is made of an offset‐shaped reflector fed by a corrugated conical horn with a rotationally symmetric beam. As a shaped reflector synthesis, an efficient and accurate method is proposed, which is a combination of the geometrical optics method and the physical optics method. To produce the high gain part of the shaped beam (beam nose), the method of a doubly curved reflector is extended so that the main part of the reflector surface is obtained in the geometrical optic process. Next, to form the low gain part (beam skirt), the physical optics shaped reflector design method is applied to an upper portion of the reflector. By defining the boundary shape of the reflector on the cone with a horn as the vertex and the flare angle from the horn axis constant, the control of the illumination level over the entire reflector edge is low and uniform regardless of the polarization, thereby improving the sidelobe characteristics. The measured radiation characteristics of the test antenna are extremely good so that the validity and effectiveness of the present antenna design are proven. The measured values include the simulated experimental results in the case where rain drops are attached to the radome.