A low-profile spiral antenna composed of a small number of turns is developed as a radiation element for circular polarisation. The spiral is fed without a balun circuit from a coplanar strip line located in the middle of two conducting planes. The upper plane has a circular aperture for the spiral to radiate. The spiral arm is optimised for 11.85 GHz. An array antenna consisting of four spirals is fabricated and the radiation characteristics are presented.
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