January 1973 | NTIA Technical Memo OT TM 73 145C
Evaluation of Beverage antennas for HF, over-the-horizon radar applications
Herman V. Cottony
Abstract: A novel, five-wire, rhomboid-shaped Beverage developed at Rome Air Development Center, Griffiss AFB, is examined from the standpoint of its applicability to HF, over-the-horizon radar. Both receiving and transmitting applications are considered. The antenna is viewed as a four-terminal network connecting electronic equipment with transmission medium. As such, its important properties are: (1) the input terminal impedance to ensure proper transfer of signal power to or from electronic equipment, (2) internal efficiency, and (3) radiating properties. The last include polarization, radiation pattern, interaction with adjacent antenna elements, etc. Principally because a Beverage antenna is terminated in a resistor, it has potentially excellent input impedance characteristics. An additional factor contributing to uniform impedance over a wide frequency range is ground losses. A few minor features in the design which may detract from the uniformity of surge impedance are mentioned. Proximity to lossy ground suggests significant attenuation of current along the conductor of the antenna. Attenuation figures from 6 to 23 dB have been measured. Expressions for gain patterns of Beverage antennas which take this attenuation into account are derived. Scaled-model measurements on two Beverage antennas were carried out. Good agreement in both the absolute gain and the general shape of the gain pattern between computed and measured results was observed. Gain patterns in elevation in the vertical plain (in forward direction) and in azimuth (at 100 elevation angle) were computed and plotted for 5, 15, and 25 MHz. Merits and shortcomings of the Beverage antenna for transmission and reception are discussed.
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