Reduction of Truncation Errors in Planar, Cylindrical, and Partial Spherical Near-Field Antenna Measurements

Abstract

A method to reduce truncation errors in near-field antenna measurements is presented. The method is based on the Gerchberg-Papoulis iterative algorithm used to extrapolate band-limited functions and it is able to extend the valid region of the calculated far-field pattern up to the whole forward hemisphere. The extension of the valid region is achieved by the iterative application of a transformation between two different domains. After each transformation, a filtering process that is based on known information at each domain is applied. The first domain is the spectral domain in which the plane wave spectrum (PWS) is reliable only within a known region. The second domain is the field distribution over the antenna under test (AUT) plane in which the desired field is assumed to be concentrated on the antenna aperture. The method can be applied to any scanning geometry, but in this paper, only the planar, cylindrical, and partial spherical near-field measurements are considered. Several simulation and measurement examples are presented to verify the effectiveness of the method.

Reconstruction of the Field Distribution on Slot Array Antennas Using the Gerchberg–Papoulis Algorithm

“…In spherical near-field measurements, the whole visible region of the PWS can be calculated from the far-field pattern. In the far-field pattern, the PWS could be accurate in the whole visible region, but when the spherical near-field acquisition is truncated (or in a general way in the case of planar or cylindrical acquisition), the reliable region is reduced [17].…”

“…The G-P algorithm has been applied to planar near-field measurements to reduce the truncation error and to reconstruct the full far-field pattern [20]. The G-P algorithm has also been applied to cylindrical and spherical near-field measurements [17]. In [17] and [20], the information of the shape of the AUT is used as a priori information, and only the visible region of the PWS is extrapolated from the reliable region of the PWS because the invisible region is not required for calculating the far-field pattern.…”

“…Due to the truncation errors, the reconstructed far-field pattern is not correct outside the valid angles, which correspond to the direction of the rays from the edge of the antenna aperture to the edge of the scanning surface. In the spectral domain, the PWS that corresponds to the scanning area is called the reliable region [17], [20]. The scanning surfaces and reliable regions for the planar and spherical near-field measurements are shown in Fig.…”

Improvement of antenna measurement results at low frequencies by using post-processing techniques

“…Recent publications also use information about the AUT in an iterative algorithm to extrapolate the reliable portion of the calculated far-field pattern. This method was proposed for the planar near-field case in [23] and generalized for the most common measurement systems in [24].…”

Overview of Novel Post-Processing Techniques to Reduce Uncertainty in Antenna Measurements

“…However, the method is only validated here for the CNF case. Other validations for other types of acquisition can be found in (Cano, 2012). For the experiment, a measurement in the CNF range at the UPM was performed.…”