Dual Linearly-Polarized Unit-Cells With Nearly 2-Bit Resolution For Reflectarray Applications In X-Band

A fully reconfigurable dual linearly-polarized phase-shifting unit-cell for reflectarrays is proposed in X-band. It consists of two orthogonal and symmetrical cross-type printed triangular dipoles loaded by 2 × 4 pin diodes. To keep independent phase responses both in vertical and horizontal polarizations and to minimize cross-polarization (by preserving the cell symmetry), the diodes are driven by pairs, leading to a maximum possible phase resolution of 2 bits per polarization. Two alternative solutions are described to bias the diode pairs. The corresponding phase responses of the unit-cell are compared for symmetrical and non-symmetrical diode loading of the dipole arms. The numerical results show that the biasing solution with no central via is more robust. They are validated experimentally around 8 GHz. The measured average loss and equivalent bit resolution at the central frequency equal 1.25 dB and 1.8 bit respectively.