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Abstract
Archimedean spiral is a broad band antenna. It belongs to the general class of antennas known as “Frequency independent antenna”. The present paper describes one such antenna developed by the authors. By backing a printed circuit spiral with a cavity of special design, a unidirectional tear drop radiation pattern is obtained. The design of broad band cavity present special problems which have been discussed. A wide band Balun transformer has been developed for matching the input impedance of the spiral to a 50 ohms coaxial cable and also for obtaining balance to unbalance transformation.