Illuminating curved passive reflector with defocused parabolic antenna

A simple expression of the gain of a curved passive reflector antenna is given. It is found that the antenna system gain is maximum if the operating wavelength times the tower height is made equal to twice the product of the radii of the curved passive reflector and its illuminating parabolic antenna. It is shown that the effective radius of the illuminating antenna may be varied by moving its feed away from the focus toward the reflector, and that the gain of the curved passive reflector antenna may be maximized by this feed defocusing technique. This method of gain maximization is very useful in practice in view of the fact that the other three parameters cannot be easily varied without effect on other design factors of a microwave relay system.