The effect of phase and amplitude quantization on the axial ratio quality of mm-wave phased-arrays with sequential rotation

Several future portable/mobile applications operating at mm-wave frequencies will require circular polarization. At the same time, these applications need to use a phased-array concept in order to cope with the associated free space path loss. By sequentially rotating linearly-polarized antenna elements, circular polarization can be obtained in a phased-array. Calibration is required to obtain a low axial ratio when scanning the beam off-broadside. The purpose of this paper is to show the effect of phase and amplitude quantization on the calibration accuracy of the axial ratio. Measured results from a 60 GHz demonstrator are used to investigate the required accuracy of the phase- and amplitude setting of each of the array elements. It is found that an accuracy of 4 bits results in an axial ratio of 0.73 dB rms for scanning between +/-30°.