A novel antenna for mobile radio relay operation in the UHF range

A novel type antenna configuration called the "Double-Rhombic" has been designed and constructed for use with mobile radio relay systems operating in the frequency range from 400 to 600 mc. This configuration is formed by combining two rhombs whose planes form an angle with each other and which have a common diagonal. The input and output terminals of both rhombs are connected in parallel with each other. A 60 degree angle between planes was found to be optimum on the basis of full scale radiation pattern measurements. By proper choice of diameter and taper of the antenna conductors the input and terminating impedances were finally adjusted to a nominal 300 ohms. A 50 to 300 ohm compensated bifilar coil balun transformer was designed to transform from a 50 ohm coaxial input to the balanced antenna input. At the terminating end a similar balun was utilized in reverse to match to a 50 ohm, 5 watt coaxial termination. The antenna is capable of handling approximately 100 watts of power. Its gain compared to the standard Radio Relay Set AN/TRC-24 Band "D" dipole array varies from -2.0 to +2.5 db over the frequency band. The SWR was found to be less than 1.4 to 1. The antenna is so mechanically designed that it is relatively light, in view of its fairly large dimensions, being in the order of 25 lbs. It is constructed of thin-walled aluminum tubing and employs "girder-type" support in its fabrication. It has a very low wind drag when compared to other antennas utilized in the same range. The antenna is also capable of being assembled and disassembled in a very short time and therefore is very attractive for use in military applications for mobile radio relay operation in the UHF frequency range.