DETERMINING THE POLARIZATION PROPERTIES OF AN ANTENNA USING ARBITRARYAND UNKNOWN FIELD PROBES

The phase-amplitude technique can provide a complete description of th e far-field characteristics of an antenna, including a total descripti on of its polarisation properties, but it requires two field probes wi th orthogonal and precisely known properties. A new calibration method for a phase-amplitude measurement is presented, which requires no a p riori knowledge of the polarisation properties of the probes. The pola risations of the two probes should be different, but they need not be orthogonal. The probes are calibrated, using one simply constructed li nearly polarised antenna, within the same arrangement where the antenn a under test is measured. The speed and simplicity of the phase-amplit ude measurement technique can then be exploited; for example, measurem ents can be made with different physical arrangements to average out t he 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 metho d, highly linear probe antennas were deliberately degraded; after reca libration, identical results were obtained within the limits imposed b y the range. Errors arising from imperfections in the linearly polaris ed calibration standard, and from mechanical errors in its placement, are discussed.