AN UNCOMPROMISING DUAL FREQUENCY ANTENNA FOR TELEMETRY TRACKING APPLICATIONS

Abstract

Currently, the majority of telemetry tracking systems in use throughout the world operate in the S-Band frequency range. While this frequency band serves as an adequate vehicle for most applications, some require an additional higher frequency for high bit-rate data. This requirement necessitates use of a dual frequency antenna and, more often than not, suffering an attendant performance compromise at both frequencies which is typically realized in such a device. One agency had such a requirement but was unwilling to accept the usual compromise in the S-band and X-band down-links used in aircraft testing. The design implemented by EMP Inc. satisfied the S-band requirements with the reputable, EMP developed, RADSCAN conical scan feed positioned at the focal plane of an eight foot paraboloidal reflector. The RADSCAN feed radome was redesigned, shaping the frontal surface to form a hyperboloidal dichroic subreflector for the X-band Cassegrain antenna. The subreflector was transparent to S-band while presenting a highly reflective surface to X-band energy. The hyperboloid was fed by a profiled corrugated horn mounted at the vertex of the paraboloidal reflector. The X-band Cassegrainian system produced optimum performance with no degradation whatsoever from the S-band Newtonian antenna. The degradation of the S-band system was less than 0.15 dB. The system provided simultaneous reception of both bands with collimated beams. The S-band system also included a side lobe comparison antenna which precludes acquisition of a target vehicle on a side lobe.