Measuring accurate low cross polarization using broad band, dual polarized probes

There are a number of near-field measurement scenarios where the use of broad band probes is desirable. These probes allow one to make the most efficient use of chamber occupancy time by covering a wide bandwidth using a single probe in place of a collection of narrow band probes. Dual-polarized probes allow one to further reduce test time by a factor of two by eliminating the need to rotate the probe by 90 degrees to perform two-polarization antenna measurements. However, the reduction in test times yielded using these probes can also lead to a decrease in performance if the probe is not properly calibrated. This paper will describe a procedure to calibrate both the pattern and polarization properties of broad band, dual-polarized probes for use in near-field antenna measurements. Results of the calibration procedure for two of these probes will be presented here. Once calibrated, these antennas were used to measure the performance of standard gain horns (SGH) and compared to baseline measurements acquired using a good polarization standard open-ended waveguide (OEWG). Examples of these results from 300 MHz to 12 GHz will be presented.