Supporting Wide-Band Circular Polarization: CRLH Networks for High-Performance CP Antenna Arrays

Supporting wide-band circular polarization (CP) over broad bandwidths poses a significant challenge for patch antennas and arrays. In any CP antenna, not only must the antenna's impedance-matching requirements be met; the circularity of the radiated wave polarization must be considered as well [1]. The circularity can be defined by a wave's axial ratio (AR), which describes the variation of the instantaneous electric field magnitude versus time. An AR of lower than 3 dB is usually sufficient to ensure good circularity, although many high-performance applications demand 1 dB or less. The difficulty is in the timing of the two polarizations created to form the CP wave. At microwave frequencies, even errors on the order of tens of picoseconds can dramatically worsen the circularity.