A study of an Archimedes spiral antenna

The gain, radiation pattern, and input impedance of a planar two-arm Archimedes spiral [Bawer and Wolfe, 1960] fed by a Marchand balun [Cloete, 1980] and designed for 2 to 6 GHz are presented. The self-complementary spiral pattern was etched onto a thin copper clad dielectric substrate and mounted 30 mm above a circular conducting ground plane with diameter 400 mm or 800 mm using a polystyrene foam spacer with open sides. The spiral was not backed by a closed cavity with conducting side walls. The paper tests a thin wire moment method code, developed for the analysis of planar spiral antennas on dielectric substrates, by comparing numerical predictions with measurements made in a 10/spl times/5/spl times/5 m anechoic chamber using an HP 8510C network analyzer. The formulation used is that of Mosig and Gardiol [1985]. For the purpose of the numerical analysis the two-arm spiral was assumed to be mounted above an infinite, perfectly conducting ground plane and to radiate into semi-infinite free space. The results of the code were also compared with numerical results published by Nakano et al. [1988].<>