An Ultrawideband Spiral Antenna With a Stable Phase Center

This article introduces an ultrawideband antenna with stable phase center and circular polarization. The proposed antenna is a low-profile cavity-backed spiral antenna measuring 58 x 58 x 50 mm(3), where the cavity is partially filled with an absorber. Throughout the desired frequency range of 2 GHz to 18 GHz, the antenna maintains a return loss better than 10 dB; the phase center offset remains within 10 mm in the direction of radiation and 4 mm in the plane of the spiral arms, the phase center variation is less than 6 degrees; and the axial ratio of less than 3 dB. Fabrication and measurements of the antenna serve to validate its performance.