Antenne spirales équiangulaires planes á quatre brins Ã\xa0 réflecteur conique et Ã\xa0 cavité, encastrée dans une structure (Plane equiangular 4-arm spiral antenna with conical reflector and cavity, fitted into a structure)

We present an experimental study of the radiation characteristics of a plane equiangular 4-arm spiral antenna with conical reflector and cylindrical cavity, fitted into a structure. When the spiral is on a level with the aperture of the cavity, the antenna is frequency independent. The bandwidth is greater than an octave (1 :2.66). When the spiral is included in the cavity, the antenna radiates as a circular aperture with equality of the E¿ and E¿ components over a 1 : 1.71 bandwidth and is no longer frequency independent. In all cases studied, the antenna possesses yery good symmetrical radiating patterns and circular polarisation.