High-Gain Antennas for VHF Scatter Propagation

Rhombic antennas were the first type employed in the study of propagation via ionospheric scatter. By the use of electrically long leg-lengths gains of the order of 20 decibels were obtained. Experimental measurements using model techniques indicated that assumptions usual in the design of rhombic antennas remained valid even for leg-lengths of 25 to 40 wavelengths. In order to obtain a more compact antenna, while retaining the gain, experimental investigation was carried out on corner-reflector and Yagi-types of antennas. By the use of 60 degree corner-reflector and a collinear array, a corner reflector antenna having gain of 19.9 db. was constructed. By exercising care in adjusting the lengths of parasitic elements, a Yagi antenna, 4.2 wavelength, having a gain of 14.2 decibels, was designed. An array of four such Yagis, having a horizontal spacing of 1.8 wavelengths and a vertical separation of 1.6 wavelengths was measured to have a gain of 19.0 decibels. Full scale corner-reflector antennas and Yagi antennas have been erected and have proved to be operationally satisfactory.