K/Ka-band transmitarray antennas based on polarization twisted unit-cells

This paper presents a dual-band dual linearly polarized transmitarray unit-cell designed for satellite communications in K/Ka-band (down link: 18.8-21 GHz; uplink: 27.5-31 GHz). Single-band unit-cells with linear orthogonal polarizations are firstly designed separately in each band. Their frequency response shows a -10-dB impedance bandwidth of more than 9% around 29 GHz and 19.5 GHz, with a 180° phase-shift in both bands. Those unit-cells are optimized with the same periodicity (6 mm, which is equivalent to 0.58-wavelength in free space at 29 GHz). The extremely low mutual coupling between these unit-cells allows designing a dual-band transmitarray by simply interleaving two single-band subarrays operating in the up- and down-links. Single- and dual-band transmitarray antennas are designed to validate the proposed concepts and demonstrate that they exhibit similar radiation performance in both bands, thereby proving the relevance of the proposed interleaving technique. Experimentally, the maximum gain obtained at 29 GHz and 19.5 GHz for a beam pointing at boresight reaches 26 dBi and 23 dBi respectively, with a side lobe level better than -20 dB at both frequencies.