Abstract
Abstract. The far-field behavior of an antenna under test (AUT) can be obtained by exciting the AUT with a plane wave. In a measurement, it is sufficient if the plane wave is artificially generated in the vicinity of the AUT. This can be achieved by using a virtual antenna array formed by a probe antenna which is sequentially sampling the radiating near-field of the AUT at different positions. For this purpose, an optimal filter for the virtual antenna array is computed in a preprocessing step. Applying this filter to the near-field measurements, the far-field of the AUT is obtained according to the propagation direction and polarization of the synthesized plane wave. This means that the near-field far-field transformation (NFFFT) is achieved simply by filtering the near-field measurement data. Taking the radiation characteristic of the probe antenna into account during the synthesis process, its influence on the NFFFT is compensated. The principle of the plane-wave synthesis and its application to the NFFFT is presented in detail in this paper. Furthermore, the method is verified by performing transformations of simulated near-field measurement data and of near-field data measured in an anechoic chamber.
Highlights
Today’s wireless communication, radar or direction finding systems make use of electrically large antennas like parabolic reflectors or antenna arrays to generate far-field radiation characteristics suitable for the particular application
After fabrication the far-field of the antenna under test has to be examined by measurements to verify that it meets the requirements on phase and magnitude
The radiated fields of the antenna under test (AUT) and the probe are usually represented by a truncated series of orthogonal spherical, cylindrical or planar field modes to formulate a transmission equation describing the coupling between both antennas (Hansen, 1988)
Summary
Today’s wireless communication, radar or direction finding systems make use of electrically large antennas like parabolic reflectors or antenna arrays to generate far-field radiation characteristics suitable for the particular application. The probe which is sampling the near-field successively at different locations is considered to form a virtual array of probe antennas on a measurement surface. This array is used to synthesize a plane wave in the vicinity of the AUT through a weighted superposition of the fields radiated by the elements of the virtual probe antenna array.
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