A Broadband Shared-Aperture L/S/X-Band Dual-Polarized Antenna for SAR Applications

This paper presents a novel tri-band antenna with dual polarizations and shared aperture. The proposed antenna operates at L-, S-, and X-bands with an approximate frequency ratio of 1:1.9:5.5. Three types of radiation elements resonating at different frequencies, including the square microstrip patch, microstrip dipole, and printed monopole, are interlaced in the same aperture. Printed monopole with a fork-shaped stub is adopted as the L-band element due to its wideband ability. Both the S- and X-band elements adopt a stacked structure to enhance the bandwidth. Besides, the S-band element employs a stepped gradient structure that can obtain a wider bandwidth than the normal microstrip dipole. The measured results agree well with the simulations. The measured impedance bandwidths of L-, S-, and X-bands are 21.7%, 11.6%, and 18.9%, respectively. The measured isolation at L-, S-, and X-bands is higher than 25, 38, and 29 dB, respectively. The antenna also exhibits an excellent radiation performance with the high cross-polarization discrimination at the three bands. To the best of the authors' knowledge, this is the first shared-aperture L-/S-/X-band dual-polarized broadband antenna in a true sense, which is useful for potential synthetic aperture radar applications.