Abstract
An ultrawideband stacked single-turn spiral antenna with an integrated feeding structure is presented in this communication. The proposed antenna consists of two stacked planar single-turn Archimedean spirals which are wound in orthogonal directions. By connecting these two stacked spirals through two vertical posts, the traveling-wave current path is lengthened and, hence, the operating frequency of Mode 1 is decreased. To reduce the feeding complexity, an integrated tapered microstrip line is used to feed the spiral, which also acts an impedance transformer. It is demonstrated that the proposed antenna can operate across 0.29-5 GHz with |S 11 | < −10 dB and 0.75-3.64 GHz with axial ratio (AR) < 3 dB. Compared with the single-turn Archimedean spiral with the same radius, the impedance and AR bandwidth of the proposed antenna are enhanced from 5:1 to 17:1 and from 1.6:1 to 4.9:1, respectively, showing that the proposed antenna can be a good candidate for ultrawideband applications.