An Intelligent Electronically Spinning TACAN Antenna

A TACAN (Tactical air navigation) beacon antenna system prototype development for use as an en-route and/or terminal navigation aid is described. This electronically spinning (900 rpm) antenna operating over the 962 to 1213 MHz band is realised by a cylindrical array formed by 32 vertical microstrip dipole line arrays fed by a novel microprocessor controlled low loss azimuth modulation network for which a patent application has been filed. This unique new network incorporates a moderate loss thinned Butler Matrix with an extremely low loss radial waveguide power splitter in a novel way forming a modified Butler Matrix which when driven by only two dual conjugate (`see-saw') PIN diode shifters provides the desired azimuth modulation with low overall loss. This feature allows the vertical line arrays to exhibit higher losses while still achieving the required system gain; thus, simple low cost microstrip construction of the vertical line arrays is possible. This represents an advantage over previously reported systems [1,2,3]. Microprocessor control provides: BITE (built in test equipment), monitoring, self calibration and self alignment under varying environmental and fault conditions which renders the system intelligent. All microwave components required in the system have been custom designed to facilitate a cost effective system which is easily maintained by virtue of its integrated modular construction. The design, manufacture (including photographs of all hardware) and measured performance is described.