Planar Near-field Measurement Techniques

Near-field antenna measurements have become widely used in high-performance antenna testing since they allow for accurate measurements of antenna patterns in a controlled environment. Near-field scattering measurement also ranks among one of the most promising methods for radar-cross-section (RCS) measurements of complex targets. Several key problems in planar near-field measurements are discussed in this paper.The first half part concerns the software development of radiation near-field measurements. First, the principles of planar wave expansion and the theory of probe compensation are introduced. 2-D near-to-far field FFT transform formulas comprising probe correction are deduced. Main error sources in ultra-low-side-lobe antenna measurements and the corresponding error correction methods are listed. Second, two antenna models are built and their near-field electric distributions are calculated by numerical methods. The far-field patterns are obtained from these simulated near-field measuring data. Last, the error-upper-bounds evaluation expressions of antenna pattern errors, caused by the finite scanning truncation errors, probe location errors are derived and their effects are qualitatively analyzed by computer simulation method.The second half part discusses some important techniques in near-field scattering measurements, such as synthetic plane waves, data-processing and reliable angle range. With a two-dimensional cylinder as a target to be measured, bistatic near-field scattering measurement is computer simulated. An effective and reliable near-field data-processing method is confirmed and a principle on choosing the width of the scanning plane is presented and proved.The simulated far-field patterns in this paper are in good agreement with exact analytic results, which shows the validity and advantage of the methods. The use of rapid algorithm reduced computing time greatly.