Abstract: There is disclosed herein an antenna for generating a rotating pattern. The pattern is generated electronically, and no physically moving parts are required. An exemplary embodiment of the antenna radiates a cardioid pattern which rotates at a 15Hz rate for use as a Tacan beacon. The structure of the antenna is in the form of a conic monopole above a ground plane. A plurality of vertical modulator fins, providing controllable shorting elements, and a plurality of suppressor posts are added. The modulator fins have associated diodes to which are applied a bias current along with modulating signals which cause the resistance of the diodes to vary with respect to the flow of RF current at the frequencies of interest (such as in the neighborhood of 1 GHz for Tacan usage). Other details of the physical structure of the antenna are shown and described herein, as well as an electronic system for controlling the diodes.

Abstract: A demodulator produces mark and space signals in response to mark and tone signals received from a radio receiver. The signals after detection are in the form of characteristic tones and are separated by corresponding band pass filters. After separation, AM detection of the mark and space signals is accomplished in envelope detectors whose output voltages are D.C. voltages. In the absence of noise, the detector voltages are essentially a rounded off version of the binary signal (mark) and a rounded off version of the complement (space) of the binary signal.