Determining the polarisation properties of an antenna using arbitrary and unknown field probes

The phase-amplitude technique can provide a complete description of the far-field characteristics of an antenna, including a total description of its polarisation properties, but it requires two field probes with orthogonal and precisely known properties. A new calibration method for a phase-amplitude measurement is presented, which requires no a priori knowledge of the polarisation properties of the probes. The polarisations of the two probes should be different, but they need not be orthogonal. The probes are calibrated, using one simply constructed linearly polarised antenna, within the same arrangement where the antenna under test is measured. The speed and simplicity of the phase-amplitude measurement technique can then be exploited; for example, measurements can be made with different physical arrangements to average out the effects of reflections. An antenna test range is described in which this scheme was implemented, and its effectiveness demonstrated with measurements of a circularly polarised feed antenna. To test the method, highly linear probe antennas were deliberately degraded; after recalibration, identical results were obtained within the limits imposed by the range. Errors arising from imperfections in the linearly polarised calibration standard, and from mechanical errors in its placement, are discussed