Planar and Spherical Near-Field Range Comparison with -60 dB Residual Error Level
Authors: Allen Newell, Greg Hindman
Comparisons of the far-field results from two different ranges are a useful complement to the detailed 18 term uncertainty analysis procedure. Such comparisons can verify that the individual estimates of uncertainty for each range are reliable or indicate whether they are either too conservative or too optimistic. Such a comparison has recently been completed using planar and spherical nearfield ranges at Nearfield Systems Inc. The test antenna was a mechanically and electrically stable slotted waveguide array with relatively low side lobes and cross polarization and a gain of approximately 35 dBi.
The accuracies of both ranges were improved by testing for, and where appropriate, applying small corrections to the measured data for some of the individual 18 terms. The corrections reduce, but do not eliminate the errors for the selected terms and do not change the basic near-to-far field transformations or probe correction processes. The corrections considered were for bias error leakage, multiple reflections, rotary joint variations and spherical range alignment. Room scattering for the spherical measurements was evaluated using the MARS processing developed by NSI.
The final results showed a peak equivalent error signal level in the side lobe region of approximately -60 dB for both main and cross component patterns for angles of up to 80 degrees off-axis.