PLANAR NEAR-FIELD MEASUREMENTS OF LOW-SIDELOBE ANTENNAS

The planar near-field measurement technique is a proven technology for measuring ordinary antennas operating in the microwave region. The de velopment of very low-sidelobe antennas raises the question whether th is technique can be used to accurately measure these antennas. We show that data taken with an open-end waveguide probe and processed with t he planar near-field methodology, including probe correction, can be u sed to accurately measure the sidelobes of very low-sidelobe antennas to levels of -55 dB to -60 dB relative to the main beam peak. A specia l probe with a null in the direction of the main beam was also used fo r some of these measurements. This special probe reduced some of the m easurement uncertainties but increased the uncertainties due to probe- antenna interactions. We discuss the major sources of uncertainty and show that the probe-antenna interaction is one of the limiting factors in making accurate measurements. The test antenna for this study was a slotted-waveguide array whose low sidelobes were known. The near-fie ld measurements were conducted on the NIST planar near-field facility.