The bi-polar planar near-field measurement technique, part II:near-field to far-field transformation and holographic imaging methods

A novel customized bi-polar planar near-field measurement technique is presented in a two-part paper. This bipolar technique offers a large scan plane size with minimal “real-estate” requirements and a simple mechanical implementation, requiring only rotational motions, resulting in a highly accurate and cost-effective antenna measurement and diagnostic system. Part I of this two-part paper introduced the bi-polar planar near-field measurement concept, discussed the implementation of this technique at the University of California, Los Angeles (UCLA), and provided a comparative survey of measured results. This paper examines the data processing algorithms that have been developed and customized to exploit the unique features of the bi-polar planar near-field measurement technique. Near-field to far-field transformation algorithms investigated include both interpolatory and non-interpolatory algorithms due to the a typical arrangement of the bi-polar near-field samples. The algorithms which have been tailored for the bi-polar configuration include the optimal sampling interpolation (OSI)/fast Fourier transform (FFT), Jacobi-Bessel transform, and Fourier-Bessel transform. Additionally, holographic imaging for determination of antenna aperture fields has been incorporated to facilitate antenna diagnostics. Results for a simulated measurement of an array of infinitesimal dipoles and a measured waveguide-fed slot array antenna are included. Appropriate guidelines with respect to the advantages and disadvantages of the various processing algorithms are provided     

Microwave antenna imaging,diagnostics, and phaseless reconstructions

Microwave antenna imaging techniques are a practical and popular method for antenna diagnostic analysis. Phase retrieval methods, however, are just beginning to emerge as an alternative microwave antenna measurements technique when phase cannot be directly measured. This article focuses on recent advances in microwave antenna imaging, diagnostic techniques, and phase retrieval methods for bi-polar planar near-field antenna measurements. An overview of the bi-polar planar near-field technique is included. The application of optimal sampling interpolation, holographic imaging and diagnostics, and iterative Fourier phase retrieval for the bi-polar planar near-field modality is explored in detail. Experimental results for a waveguide-fed slot array antenna are presented to illustrate these methods. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 396–406, 1997     

Linear spiral sampling for the bipolar planar near-field antennameasurement technique

This paper investigates linear spiral sampling for bipolar planar near-field antenna measurements. This sampling scheme is, depending on range implementation, the most rapid polar near-filed data acquisition mode. The near-field to far-field transformation is performed using a modified optimal sampling interpolation (OSI)/fast Fourier transform (FFT) approach. Measured far-field pattern results for a waveguide-fed slot array antenna are presented and are shown to have excellent agreement with results obtained from a conventional bipolar measurement     

Application of spherical wave expansions to reflector antennasusing truncated field data

The electromagnetic field radiated by paraboloidal and hyperboloidal reflector antennas excited by an azimuthally independent, linearly polarized source is considered. The electromagnetic field is sampled on a spherical surface in order to numerically generate a set of spherical wave mode coefficients which, in turn, are used to compute antenna patterns. Patterns are produced in the near- and far-field regions based on both full and partial, or truncated, near- and far-field data as a function of the antenna parameters and the truncation angle location. The similarity of the patterns obtained from truncated field data to the untruncated patterns is found to depend on the pattern level at the truncation point, the location of the truncation point, the antenna parameters, and the radial distance between the spherical surfaces on which the electromagnetic field is sampled and produced     

Phaseless bi-polar planar near-field measurements and diagnosticsof array antennas

Antenna near-field measurements typically require very accurate measurement of the near-field phase. There are applications where an accurate phase measurement may not be practically achievable. Phaseless measurements are beginning to emerge as an alternative microwave antenna measurements technique when phase cannot be directly measured. There are many important aspects for successful implementation of a phaseless measurement algorithm. This paper presents appropriate phaseless measurement requirements and a phase retrieval algorithm tailored for the bi-polar planar near-field antenna measurement technique. Two amplitude measurements and a squared amplitude optimal sampling interpolation method are integrated with an iterative Fourier procedure to first retrieve the phase information and then construct both the far-field pattern and diagnostic characteristics of the antenna under test. In order to critically examine the methodologies developed in this paper, phaseless measurement results for two different array antennas are presented and compared to results obtained when the near-field amplitude and phase are directly measured