In massive multiple input multiple output (MIMO) arrays, Compressive Sensing (CS) has been proposed to rapidly verify the array's excitation in a production environment. All follow the general approach of creating the sparsity needed for CS by subtracting the measured far-field (FF) or near-field (NF) of the test array from that of a "gold standard" array measured under identical conditions. In several previous papers the authors have applied CS to planar near-field (PNF) measurements with a view to building a compact test facility well suited to the production environment for these antennas. In this article, we identify a fundamental flaw in the creation of the difference pattern between a gold standard antenna and the test antenna, in that the electrical path length difference between probe and gold standard antenna and that of probe to test antenna must be no more than 0.002 lambda or 0.7 degrees. Even if mechanical tolerance can achieve this, thermal drift in the radio frequency (RF) subsystem will easily reach the 0.7 degrees figure. This article then describes an analysis process that overcomes this problem, restoring the CS process to very nearly the levels of performance described in our previous publications and those of other workers. To achieve this, we have used a fixed set of NF probes located randomly over a region confined to the central part of the NF measurement plane, along with a PIN switch matrix to offer a very rapid and very consistent RF measurement. We have extensively simulated a massive MIMO array of 8 x 24 elements and found that just 25 NF probes can detect up to 2% failure rate. In addition, we present a technique to improve the accuracy of the array excitation reconstruction by using several partial excitations of the array. In this work we consider both array element amplitude and phase reconstruction performance and demonstrates that it is possible to detect a single element, phase only, fault of just 22.5 degrees.

Mode filtering has been shown to be very effective in suppressing spurious reflections in antenna measurements. Specifically, it has been well documented that in the quasi-far-field, the two polarizations are decoupled, making it possible to apply standard cylindrical near-field theory on the amplitude and phase data acquired from a single polarization measurement on a great circle cut [1]. The method was further extended to allow data collected from an unequally spaced angular abscissa by formulating the solution as a pseudo-inversion of the Fourier matrix [2]. This formulation, however, can be prone to spectral leakage because of nonorthogonality of the Fourier basis on an irregularly sampled grid, especially when the positions deviate significantly from the regular grid [2]. In this paper, we propose to use Compressed Sensing (CS) to compute the Cylindrical Mode Coefficients (CMCs), which improves the signal to noise ratio, allowing more accurate recovery of the prominent modes. The CS recovery is tenable because with the coordinate translation of the measurement pattern to the rotation center, the Maximum Radial Extent (MRE) of the antenna under test is greatly reduced, making CMCs quite sparse in the mode domain. The novel application of CS presented in this paper further expands the generality of the mode filtering method, which is now applicable to under-sampled data (at below the Nyquist rate) acquired on positions that grossly deviate from the equally-spaced regular grid.

This expanded and updated second edition with full colour images provides a comprehensive introduction and explanation of both the theory and practice of planar near-field antenna measurement, from its basic postulates and assumptions, to the intricacies of its deployment in complex and demanding measurement scenarios. The book initially examines the properties of antennas that allow them to enhance the free space interaction of electronic systems and this leads into a full description of the theory of planar near-field scanning. The utility of the planar methodology is illustrated with example measurement campaigns that include discussion of the characterisation of a wide range of antennas. The second edition brings the text right up to date. Advanced techniques including non-canonical transforms, scattering suppression techniques, equivalent current based diagnostics, extrapolation range measurements, use of multi-axis industrial robots and UAV drones for data acquisition are now included, together with a greatly expanded treatment of uncertainty analysis and planar range assessment. A large number of near-field facilities exist worldwide but to the authors' knowledge no single text provides a clear step-by-step description of all the details of the planar near-field measurement technique. All three authors have spent a significant proportion of their professional careers involved with antenna measurements and the aim of this text is to provide the reader with a complete, comprehensive, and practical text that will act as a single reference for all aspects of the measurement technique. Principles of Planar Near-Field Antenna Measurements, 2nd Edition is aimed at electromagnetics students, researchers and professionals, especially those concerned with electromagnetics metrology.

This paper presents a recent advance in designing and validating blended rolled edge (BRE) reflectors for compact antenna test range (CATR) applications. BRE reflectors offer the potential of very smooth near-field patterns in the quiet zone (QZ) due to their improved diffraction characteristics. In house equivalent currents based physical optics (PO) simulation code results were compared and validated against Altair Feko Method of Moment (MoM) simulations for various BRE reflectors. Reflector comparisons have been shown for different modelling scenarios, eg. imported CAD files versus surface created using Lua macros coding, which is a built-in macros language in Altair Feko. All results are in a very good agreement, including cross polar magnitude and phase.

This Roadmap overviews present challenges and opportunities for the development of antenna measurement techniques and technologies to support the all-pervasive and ever-increasing demand for radio-frequency wireless systems in modern society. The Roadmap comprises 19 inspiring contributions by 34 leading experts in antenna measurements.

In the quasi-far-field, the tangential orthogonal electric field components, e.g., in the phi direction and z direction (in the cylindrical coordinate system), are decoupled, which means that only the co-polarized field component is sufficient to transform a single cut antenna pattern to the cylindrical mode domain. When the antenna pattern is measured with a displacement from the center of rotation, a phase coherent mathematical translation of the pattern to the center of rotation promotes mode separation between the modes of the antenna and those of the chamber reflections. A mode filter can then be applied to remove effects due to chamber multipath reflections. In this scheme, an accurate measurement of the displacement distance from the rotation center is essential. Conventionally, this is obtained by using a physical measure, e.g. ruler, laser tracker, etc. In this study, we investigate several techniques to automatically retrieve the requisite offset distance using the vector pattern data, including using: the unwrapped phase response, through time domain transformation, and by examining mode concentration within the spectrum domain. Each method is studied for its robustness, limitations and efficiency in accurately determining the displacement distance.

: The simulation of a novel drone-based NF/FF antenna measurement system enabling the reconstruction of AUT phase and the true location of the untethered drone using multiple land-based reference antennas is described. The mathematical approach follows the principle used within GPS position and time recovery. Conceptually the satellites are replaced by ground based reference antennas of known location, the user location is now the drone location and the user clock offset is replaced by the unknown AUT phase radiated at the angle subtended between the AUT and drone location. This addresses the need for drone based NF/FF antenna measurement of large in-situ VHF/UHF antenna arrays plus the need to measure the installed performance of microwave antennas on structures such as buildings, aircraft and ships. To assess the viability a computer simulation of the measurement system is constructed and its performance analysed in terms of the accuracy of reconstruction of the AUT phase and true drone location, as well as the NF/FF radiation pattern accuracy in terms of Equivalent Multipath Level (EMPL). An example measurement ‘range’, comprising AUT location and six fixed REF antennas demonstrates wide AUT operating bandwidth of (0.5 to 2) GHz, with EMPL < -50dB over the forward hemisphere.

Compressive sensing (CS) has been deployed in a variety of fields including wideband spectrum sensing, active user detection, and antenna arrays. In massive multiple input multiple output (MIMO) arrays, CS has been applied to reduce the number of measurements required to verify the arrays excitation. To date, the literature has concentrated on the various methods of achieving CS and applying them to both linear and 2-D arrays, and aimed at detecting fully failed elements in an array, offering simple pass/fail testing. All follow the general approach of creating the sparsity needed for CS by subtracting the measured far field or near field of the test array from that of a “gold standard” array measured under exactly identical conditions. This article extended this work to the need for rapid but accurate reconstruction of element excitation in a production testing environment for massive MIMO arrays. The aim is to demonstrate that CS can offer accurate reconstruction of array excitation. Particularly, the work addresses the issues of optimal sampling, measurement noise, accuracy of faulty element detection, effects of beam scanning, and physical alignment of the gold standard array with the test array. We have restricted ourselves to considering production standard arrays with failure rates up to around 5% and conclude with a set of proposed modifications to the basic CS process as applied to array excitations that achieve a near 20 dB improvement in the accuracy of the reconstructed array excitation offering mean square errors (MSEs) near to −40 dB, with a sampling strategy of just 1.4% of the Nyquist rate. This is achieved with the number of measurements to array element size ratio of approximately 0.2.

The validity and viability of using frequency domain mode filtering to qualify an EMC chamber above 1 GHz has been demonstrated in a previous study [1]. The novel approach overcomes the difficulties with under sampling encountered in the traditional spatial sampling method adopted by CISPR 16-1-4, and it also has the distinct advantage over the time domain method adopted by ANSI C63.25.1 in that broadband and low ring-down antennas are not required. In this study, we further examine one of the assumptions made in the previous study to translate the quasi-far-field pattern to the rotation center. The approximate method is compared to a more rigorous method by using a quasi-far-field to far-field transformation first before applying the phase translation and subsequent mode filtering. In this paper, we further validate the method by conducting an intercomparison study based on measurements conducted in a 3 m anechoic chamber to show the correlations of the mode filtering method to the CISPR and the time domain (TD) site VSWR methods. We demonstrate how the proposed method improves the test repeatability, lowers measurement uncertainties, and increases measurement efficiencies.

Anechoic chambers used for electromagnetic compatibility ( EMC) measurements above 1 GHz are qualified based on the site voltage standing wave ratio (SVSWR) method as per the international standard CISPR 16-1-4. With one antenna at the fixed position, some distance away from the quiet zone (QZ), the SVSWR is acquired by moving a dipole-like antenna along several linear paths that are located at the edge of the QZ. To reduce test burden, the SVSWR method under-samples the measurement by design, in that only six discrete points along each 40 cm linear travel path are measured. As a result, the test results are generally overly optimistic. In this article, we propose to use a novel cylindrical mode coefficient (CMC)-based frequency domain mode filtering techniques to obtain the VSWR. Here, we measure the vector pattern cut of the dipole-like test antenna with an offset placement at the outer edge of QZ. The antenna is then mathematically translated to the rotation center, whereupon a bandpass filter that tightly encloses the test antenna mode spectrum is applied. Two approaches are studied herein for translating the rotation center. One is by applying a path length correction to both magnitude and phase, and the other is by performing a cylindrical far-field transformation on the quasi-far-field data. The difference between the mode filtered antenna pattern and the original perturbed pattern is used to derive the chamber SVSWR. In contrast to the conventional technique, the proposed, novel method does not suffer from positional under-sampling, so it is well-placed to be applied at microwave frequencies and above.

While the size of the reflector in general determines the usable area of the quiet zone inside which plane wave conditions are found, the edge treatment also plays a significant role in terms of overall quality and electromagnetic field distribution. Using modern fast simulation technology in combination with genetic optimisation, the edge treatment can be optimised specifically for a compact antenna test range as part of the design process. This is crucial as it maximises the efficiency with which the available space is used and therefore minimises the costs of implementation of a new facility. This is particularly important in 5G applications where multiple systems are typically required with any economies becoming multiplicative. Several commonly encountered reflector edge treatments are examined with the quiet-zone performances compared against that of an alternative genetically optimised serration design.

The reconstruction of embedded element patterns is analyzed in physically and electrically large aperture arrays from near-field measurements taken with a source carried by a drone. This is a very challenging metrology problem, especially when the arrays are composed of wide-band wide field-of-view antenna elements in a highly coupled environment, as is the case for the SKA-low radio telescope stations. We study the use of both a direct near- to far-field transformation and a model-based approach to overcome the limitations imposed by this type of complex electromagnetic structures. Both methods are explained using a decomposition of the antenna voltages in terms of a spectrum of incoming plane waves. A numerical example with an irregular array of 16 log-periodic elements and a hemispherical path shows their abilities to capture the mutual coupling effects.

Unmanned Aerial Systems (UAS), colloquially known as drones, offer unparalleled flexibility and portability for outdoor and in situ antenna measurements, which is especially convenient to assess the performance of systems in their realworld conditions of application. As with any new or emerging measurement technology, it is crucial that the various sources of error must be identified and then estimated. This is especially true here where the sources of error differ from those that are generally encountered with classical antenna measurement systems. This is due to the larger number of mechanical degrees of freedom, and to the potentially less repeatable and controllable environmental conditions. In this paper, the impact of some of these various error terms is estimated as part of an ongoing measurement validation campaign. A mechanically and electrically time invariant reference antenna was characterized at ESA-ESTEC's measurement facilities which served here as an independent reference laboratory. The reference results were compared and contrasted with measurements performed outdoors at Quad-SAT's premises using QuadSAT's UAS for Antenna Performance Evaluation (UAS-APE). While a direct comparison between the measurement results from ESA-ESTEC and QuadSAT delivers information about the various uncertainties within a UAS-APE system in comparison to classical measurement facilities' and the validity of such a system for antenna testing, other tests aim at providing an estimation of the impact of each error source on the overall uncertainty budget, thus paving the way towards a standardized uncertainty budget for outdoor UAS-based sites.

This chapter aims to address the need to perform near-field antenna measurements with improved flexibility as compared to the traditional approaches of canonical measurement surfaces using regular sampling. Inverse equivalent source solvers (IESSs) are derived for the transformation of measured near field data into a set of equivalent sources, which can in turn be used to calculate near- and far-fields anywhere in the solution domain. This enables near-field antenna measurements to be made on non-canonical surfaces and/or with irregular grids. A by-product of these IESSs is that they allow a very flexible modelling of the antenna under test (AUT), which can, with the inclusion of a priori knowledge about the geometric extent of the AUT, provide 'measured' currents on the antenna structure.

This greatly expanded, co-authored, two-volume text provides a comprehensive introduction and explanation of both the theory and practice of modern antenna measurements, from their most basic postulates and assumptions, to the intricate details of their applications in various demanding modern measurement scenarios. Starting with an initial examination of the properties of antennas that allow them to enhance the free-space interaction of electronic systems, the authors then introduce direct far-field and indirect far-field forms of antenna measurements and their various implementations. Detailed descriptions are given of the direct far-field measurement technique CATR (Compact Antenna Test Ranges), Body-Centric measurements, and detailed developments of standard planar, cylindrical, spherical and non-canonical near-field techniques; and includes a through treatment of near-field range error budgets which are an indispensable part of antenna metrology. The books conclude with recent advances in measurement techniques such as aperture diagnostics, phase-less antenna metrology, error correction, and range multi-path suppression techniques. Extensive examples illustrate the concepts and techniques covered. This second edition is thoroughly expanded and now includes new chapters on near-field to far-field transforms from non-canonical surfaces, electromagnetic modelling of CATRs and near-field antenna measurement systems. In addition there is an expanded chapter on coordinate systems, polarization bases and antenna pattern plotting and new sections on more specialized topics such as 5G and Radome measurements.

Reflections in antenna measurement ranges generally comprise the most significant term within the overall uncertainty budget [1, 2]. For well over a decade now, a frequency domain mode filtering based measurement technique has been utilized to significantly reduce range reflections within antenna test systems [1, 3, 4, 5, 6, 7, 8]. More recently however, this technique has been adapted so that it could also be used with far-field and compact antenna measurement systems [9, 10, 1] with the technique being firmly rooted in conventional cylindrical near-field theory [1]. Although this family of techniques was initially intended to provide a means by which the lower frequency limit of operation of a given facility [3, 4] could be extended downwards to work effectively in applications where the operation would otherwise be impaired by the fixed physical size of the absorber and therefore predetermined electrical performance, these techniques have more recently been used very successfully to improve performance at the upper end of the frequency extent [11]. Although this technique has been extensively examined and verified empirically by means of range measurements, relatively little verification by means of computational electromagnetic simulation is available in the open literature [1, 12, 13, 14, 15]. In this paper, we developed an efficient computational electromagnetic (CEM) model of the measurement configuration, i.e. a digital twin, using a three-dimensional, full-wave CEM solver. The purpose of this is to construct an absolute truth-model to provide a firm basis for a detailed quantitative examination of the scattering suppression technique. The modelling technique is discussed in detail and initial results are presented which show very good agreement between the "true" far-field pattern of the antenna in free space and that of the far-field of the antenna when perturbed with the presence of a scatterer and applying the scattering suppression process.

The Compact Antenna Test Range (CATR) is a long established, general purpose, wide-band, test methodology for acquiring far-field radiation characteristics within comparatively small test volumes [1]. By projecting an image of the CATR feed at infinity through field collimation, typically achieved by means of reflection, the CATR synthesizes the type of wave-front that would be incident on the antenna under test (AUT) if it were instead located at a position very much further away from the feed than is actually the case. By recording the coupling of this collimated pseudo plane-wave into the AUT for different orientations, we may obtain the classical measured "far-field" radiation pattern in real-time. Thus, the quality of the CATR pattern measurement is primarily determined by the uniformity and purity of the phase and amplitude of the pseudo plane-wave [2], [3], [4]. Thus, the performance of the range is largely, but not completely, crystallized at the time that the reflector and feed are fabricated and installed with scope for a posteriori performance improvements being relatively limited. However, even here, uses of advanced post-processing techniques have recently been shown to provide worthwhile benefits to the facility-level uncertainly budget and crucially, these too can be verified and developed in conjunction with electromagnetic simulation [1].Thus, the successful development and deployment of CATRs has, necessarily, been predicated upon a corresponding development in the speed, accuracy and sophistication of the attendant CATR electromagnetic simulation software. Recent developments in CATR simulations have enabled the design and realization of increasingly complex and ever more efficient CATR assemblies that span progressively wider frequency ranges. These end-to-end simulations, which increasingly harness and rely upon parallel processing architectures, can now be used to determine the impact of the precise CATR design on over-the-air (OTA) communications system parameters. This therefore paves the way for the design and development of CATRs that are fully optimized for the test, calibration and OTA measurement of demanding mm-wave massive multiple input, multiple output (MIMO) backhaul antenna systems. This is particularly important as interest has largely shifted away from traditional antenna performance metrics and instead is focusing on communication system figures of merit [5], [6]. Similarly, sophisticated post processing techniques now enable communication system level parameters such as far-field error vector magnitude (EVM), bit error rate (BER), signal-to-interference-plus-noise-ratio (SINR), etc. to be derived conveniently and efficiently from conventional ranges without the need for additional, expensive, specialist RF instrumentation.This paper presents an introduction to the CATR, the simulation and data post-processing highlighting some of the more significant developments while focusing on those aspects that are most pertinent to modern communication systems which are essential for the successful roll-out of 5G.

For any indoor antenna test range (planar/cylindrical/spherical/compact), room scattering is one of the most significant terms within the overall uncertainty budget, especially when the range is pushed to operate outside its optimal working frequency range, either lower or higher than its designed frequency range. A frequency domain mode filtering based measurement technique has been used to reduce the range scattering in the past decade. Although this technique has been extensively examined and validated through measurements, comparatively little validation has been reported using full-wave three-dimensional computational electromagnetic (EM) simulation because of the huge computational effort required. Built upon the successful, recent, development of an EM model for cylindrical mode based far-field antenna scattering suppression, that study is extended to consider the more complicated case of the spherical far-field range. For the first time, an EM model of the spherical far-field measurement was constructed and used to verify this measurement and post-processing technique. The EM modelling technique is detailed, and initial results are presented which show good agreement between the "true" far-field and the perturbed far-field with scattering suppression processing having been applied. The criterion of how to select the transformation centre point for optimal scattering suppression is examined and best practice proposed.

Traditional measurement methods assume that very accurate antenna to range alignment of the antenna under test (AUT) is convenient or possible. It has recently been shown that the use of non-rectilinear co-ordinate systems are of particular use for the purpose of correcting antenna to range misalignment. Additionally, this misalignment correction can be used to construct an extended composite measurement plane from a series of mis-aligned scans that themselves can be considered as constituting a polyhedral measurement surface. This paper describes the additional processing that is required to yield corrected near and far field data from an acquisition of a mis-aligned AUT. This technique is then illustrated with example results. The agreement of the corrected results is determined via the application of image classification techniques which correlate antenna patterns in a reduced vector pattern space in terms of their overall global features.