High-power, broad-bandwidth HF dipole curtain array with extensive vertical and azimuthal beam control

The design, construction details, and performance of a prototype high-power HRS 12/6/.5 antenna system covering the 6 to 26 MHz international broadcast bands are presented. The antenna has been developed, erected, and tested as part of the Voice of America modernization program to demonstrate the feasibility of controlling the horizontal and vertical apertures and beam directions of high-power, broad-bandwidth (2:1 frequency ratio) antennas. The antenna system provides 11 vertical slews, 15 azimuthal slews, and five azimuthal widths. The peak of the elevation pattern can be steered to angles of 4° to 20° above the horizon and the azimuthal beam can be steered up to ±30° with respect to boresight. Gains range from 16 to 31 dBi. Azimuthal beamwidths between -6 dB points range from 8° to 75°. The antenna is designed to handle the input power of one or more 500-kW double-sideband, amplitude-modulated transmitters. The antenna system has been designed using basic dipole and antenna switching modules from which smaller subarrays (HRS 2/6/.5, HRS 4/6/.5, HRS 8/6/.5, etc.) can be readily developed. The extensive beam control provided by the antenna system enables a shortwave broadcaster to use fewer antennas to reach the same audience. This reduces the land area of the station as well as its acquisition and operating costs