Effect of the Test Zone Field on the Radiation Characteristics of Antennas
Undesired diffractions or reflections within an antenna measurement chamber interfere with the desired signal causing a deviation from the ideal Test Zone Field (TZF). The resulting non-ideal field causes an error in the measured parameters of an antenna under test. In order to analyse the frequency-dependent error caused by the TZF in a Compact Antenna Test Range (CATR), an evaluation method is introduced which is based on spherical wave expansion. To generate the TZF data, a full-wave technique is applied on the reflector model of the CATR approximating the real existing TZF. Three measured antennas which differ in size and directivity are investigated and the corresponding differences are evaluated using the equivalent-error-signal level. It is demonstrated that test zone field compensation has to be applied in order to enable high-accuracy antenna measurements and to provide additional design possibilities of measurement ranges.