Robust 2-bit dual-linearly-polarised unit-cell for reflectarray applications

A new configuration of 2-bit dual-linearly-polarised unit-cell is introduced in X-band. It consists of two orthogonal and symmetrical cross-type printed triangular dipoles loaded by p.i.n diodes. This cell exhibits good performance with insertion loss lower than 2 dB and an isolation level better than 26 dB between both orthogonal polarisations. The impact of the diode features (off state capacitance) upon the phase response degradation is also investigated numerically. An improved cell design is then proposed to reduce the influence of the dipole loaded by non-symmetrical capacitances. This unit-cell exhibits 1.8 equivalent bit with 1.5% bandwidth obtained in measurement and a simulated cross-polarisation below -20 dB.