The planar near-field measurement of the far sidelobes of a reflector antenna

Planar near-field measurements are commonly used to measure the main beam of a narrow beam antenna such as a large reflector or phased array. However, occasions arise when one is interested in the far sidelobes (beyond 90 degrees from boresight) or backlobes of the test antenna and it is economically prohibitive to use a separate test facility to measure these sidelobes. This paper addresses the feasibility of measuring the far sidelobes of an antenna in a planar near-field range. The most important error sources are identified and one significant error source is the scan plane truncation error. A near-field data window function, which has a smooth taper at the edges of the scan plane, is used to minimize the truncation error. Finally, an example is used to demonstrate the measurement of the far sidelobes of a reflector in a planar near-field range.