Cassegrain Antenna

Cassegrain antenna [kas·gran an′ten·ə]

(electromagnetism)

A microwave antenna in which the feed radiator is mounted at or near the surface of the main reflector and aimed at a mirror at the focus; energy from the feed first illuminates the mirror, then spreads outward to illuminate the main reflector.

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Cassegrain Antenna 

(named for the 17th-century French physicist N. Cassegrain), a reflecting antenna that consists of a radiator and primary and secondary (auxiliary) electromagnetic energy reflectors (mirrors) assembled according to the scheme of a Cassegrain telescope. The Cassegrain antenna is widely used in radio communications, radar, and radio astronomy in the centimeter wavelength band.

The primary reflector, which is a paraboloid of revolution, determines the width of the directivity pattern of the Cassegrain antenna and forms a plane front of the radiated electromagnetic wave. A radiator, usually a horn, dielectric, helical, or dipole antenna, is located at the vertex of the primary reflector; such an arrangement significantly reduces the length of the lines feeding energy from the transmitter to the radiator. The auxiliary reflector, of smaller diameter, is a hyperboloid of revolution, one focus of which coincides with the focus of the primary reflector, and the second with the phase center of the radiator. A radiator with a directivity pattern of special shape and a low level of fringe radiation is used to reduce the dissipation of electromagnetic energy beyond the edges of the auxiliary reflector.

O. N. TERESHIN and G. K. GALIMOV