Test-zone field quality in planar near-field measurements

摘要

This paper reports on the results of computer simulations of planar near-field scanning and its ability to achieve an high accuracy test-zone field was defined for this study to have less than 0.2 dB peak-to-peak amplitude variation and less than 1.5 degrees peak-to-peak phase variation. This investigation sought the minimum scan length, L, for a given critical angle, theta_c and separation, S. the minimum scan length determined from this investigation is given by: L+D+2S(tan(theta_c)) + 20lambda/cos(theta_c). This scan length is approximately 60lambda larger, for a critical angle of 70 degrees, than previousl yaccepted. It is suggested that the maximum practical value of theta_c is between 60 and 70 degrees. The use of raised cosine amplitude and/or quadratic phase windows applied to the edges of the measurement plane is shwon to provide test-zone field quality improvement and/or allow scan lengths approximately 10lambda smaller.