A planar-spiral antenna to be used in an ultrawideband (UWB) radar system for heart activity monitoring is presented. ?e antenna,\r\nnamed ââ?¬Å?twin,ââ?¬Â is constituted by two spiral dipoles in a compact structure. ?e re??ection coefficient at the feed point of the dipoles is\r\nlower than -8 dB over the 3ââ?¬â??12 GHz band, while the two-dipoles coupling is about -20 dB. ?e radiated beam is perpendicular to\r\nthe plane of the spiral, so the antenna is wearable and it may be an optimal radiator for a medical UWB radar for heart rate detection.\r\n?e designed antenna has been also used to check some hypotheses about the UWB radar heart activity detection mechanism. ?e\r\nradiation impedance variation, caused by the thorax vibrations associated with heart activity, seems to be the most likely explanation\r\nof the UWB radar operation.
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