Aplanatic Reflector Antenna

a double reflector antenna with controllable change (scanning) of the direction of the maximum radiation pattern, for which the shape of the radiation pattern remains constant. Aplanatic reflector antennas are used primarily in radar and radio navigation for waves in the centimeter band. In aplanatic reflector antennas, scanning is accomplished by shifting the exciter over some optimal focal curve, with the reflectors remaining immobile (see Figure 1). The energy fed to the exciter is directed to the auxiliary reflector, from which it is reflected onto the primary reflector, whose dimensions determine the width of the radiation pattern. The auxiliary reflector is made in the form of a system of linear wires oriented parallel to the intensity vector of the electrical component of the exciter’s electromagnetic field. The intensity vector of the electrical component of the field reflected from the primary reflector is directed perpendicularly to the wires of the auxiliary reflector and thus passes through it freely. Such a rotation of the polarization plane of the field reflected from the primary reflector is accomplished by the appropriate design of the primary reflector. The ratio of the focal distances of the various rays determines the degree of distortion of the antenna pattern during scanning. Distortions are minimal (the antenna becomes aplanatic) when the focal distances of all rays are identical.

Figure 1. Diagram of the path of rays in an aplanatic reflector antenna:(A) radiator, (B) auxiliary reflector, (C) primary reflector; (6,), (B2), and (B3), points of reflection of rays from auxiliary reflector; (C,), (C2), and (C,), points of reflection of rays from primary reflector; (0,), (D2), and (D3), points of intersection of continuations of rays ABt, AB2, and AB3 with the corresponding rays C,D,, C2D2, and C3D3; (/AD,), (AD2), and (AD3), focal distances of the rays defined by the angles 0,, 02, and 03, respectively; (D) focal periphery