PURPOSE: To prevent the deterioration of gain in a beam scanning state by deciding the shape of a main reflector so as to secure the different aperture diameters in the lengthwise direction and its orthogonal direction when viewed from the main beam direction and at the same time by securing the lengthwise direction that is orthogonal to the main beam scanning direction.
CONSTITUTION: The lateral diameter of an aperture surface 2-1 of a main reflector 2-2 is set at D1 together with the longitudinal diameter set at D3. The diameter D3 is decided so that the antenna gain is equal to that of a circular aperture antenna of the diameter D2. For instance, the diameter D3 that secures an equal area is defined by D3=D22/D1 in regard of an elliptical aperture. Meanwhile the primary radiators 2-4, 2-5 and 2-6 are arranged distantly from a focal point so that the beams are radiated in the direction where they are laterally offset to the mechanical axis of the antenna. Under such conditions, the change of gain caused to the beam scanning angle is equal to the increase of gain of the circular aperture antenna of the diameter D2. Thus the deterioration of gain caused by the beam scanning can be set equal to the circular aperture antenna of the diameter D1.
KONDO AKIRA
KAGOSHIMA KENICHI
