Retrieving field magnitude and polarisation ellipse from phaseless measurements of linear polarisations, including error analysis

Antenna radiation measurements are sometimes performed without phase information. An example of this is measurements of the radiation characteristics of active devices such as mobile terminals, where the terminal is set to transmit, and no phase reference is available. In such measurements, a special technique is required if a polarisation other than that of the sensor antenna is to be measured. One such technique is to reconstruct the field ellipse from the measured levels of a set of linear polarisations. From the levels of three linear polarisations, the total power of the field, as well as the axial ratio and orientation of the polarisation, can be obtained. The polarisation sense, however, requires the level of at least one circular polarisation. So-called spinning linear measurements, where the level is sampled at well-controlled polarisation angles, is a practical implementation of the technique. The calculation of field power and polarisation axial ratio and orientation from the levels of a set of linear polarisations is presented. Also presented is an error analysis giving the errors in these calculated parameters as a function of systematic and random measurement errors. The number of measured polarisations is included as a parameter in the analysis.