Wideband Circularly Polarized Reflectarray Antenna Using Rotational Symmetrical Crossed Dipoles

A wideband circularly polarized (CP) reflectarray (RA) antenna using rotational symmetrical crossed dipoles is presented. This is the first time investigating coupled crossed dipoles as the unit cell for wideband reflection bandwidth in the CP RA design. Equivalent circuit analysis shows that when a CP wave impinges on the designed unit cell, two series resonances, and two parallel resonances are simultaneously excited on the crossed dipoles. Owing to these four different resonances, the CP reflection bandwidth is greatly improved and elaborately adjusted by controlling the coupling between the crossed dipoles. The CP reflection bandwidth ratio of the unit cell is enhanced up to 2:1 for $S_{x} < -15$ dB with a thin thickness of $0.12 \lambda {0}$. Based on this unit cell, a wideband -20° collimated CP RA antenna with a circular aperture of 316 unit cells was designed, fabricated, and measured for final performance verification. The measured results show that a wide CP bandwidth of 7.6-15.9 GHz is achieved with the axial ratio (AR) < 3 dB. In addition, the measured 3 dB gain bandwidth is better than 43.7% with a peak realized gain of 26.3 dBic and maximum aperture efficiency (AE) of 58.3%.