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This communication provides an effective two-steps strategy to compensate for known 3-D probe positioning errors occurring in the non-redundant (NR) cylindrical near-to-far-field (NTFF) transformations. As first step, a phase correction, here denoted as cylindrical wave correction, is employed to perform the correction of the positioning errors relevant to the deviations of the measured NF samples from the nominal scanning cylinder. Then, an iterative procedure will be applied to retrieve the NF samples at the points specified by the adopted sampling representation from those obtained at the previous step and affected by 2-D positioning errors. Finally, after properly reconstructing the correctly distributed cylindrical samples, the data necessary to apply the classical cylindrical NTFF transformation can be restored in accurate way by employing a 2-D optimal sampling interpolation (OSI) formula. It should be noticed as, to derive the NR sampling representation, as well as the OSI scheme, it is necessary to provide a proper modeling of the antenna under test. This modeling has been got by shaping the source with a prolate spheroid. Numerical tests will show the capability of the procedure to compensate these 3-D positioning errors.
This work aims to propose and optimise a non-redundant spherical spiral near-to-far field (NTFF) transformation for elongated AUTs from spiral near-field (NF) data acquired over the upper hemisphere due to the presence of an infinite perfectly electric conducting (PEC) ground plane. Such a technique properly exploits the principle of image and the theoretical foundations of spiral scan for non-volumetric AUTs to develop the non-redundant representation along the sampling spiral in presence of PEC ground plane and to synthesise the voltage NF data which would be acquired over the spiral wrapping the lower hemisphere. Once these voltage NF data have been synthesised, then an efficient 2-D optimal sampling interpolation scheme allows the recovering of the NF data required by the classical NTFF transformation. In the hypothesis that the AUT and its image exhibit a predominant dimension as compared to the other two ones, a prolate spheroidal source modeling is here adopted. Numerical tests show the accuracy of the developed non-redundant spherical spiral NTFF transformation.
Demand for broadband connectivity in moving platforms on land, sea, and air has opened the mass market for low-cost mobile ground-station terminals that employ electrically steerable antennas. The antennas of these terminal units need to be tested in a production line environment. Planar near-field scanning is considered as a convenient measurement method, but the time needed for conventional scanning may be prohibitive. In this paper, the design of a multiprobe planar near-field scanner for rapid antenna testing at Ku-band is presented. A probe array is moved along a spiral path to avoid large accelerations and decelerations of the probe array, and the near-field sampling is done simultaneously with multiple of respective receivers. Thus, the data acquisition time is significantly reduced compared to the single probe or receiver measurement. A preliminary antenna testsystem design for the mobile ground-station terminal antennas operating at Ku-band is presented. The numerical results for simple representative antenna models suggest good performance of the system.
We propose a compact bistatic radar cross section (RCS) measurement system using a new 2D plane-wave synthesis (PWS) employing 2D propagating plane-wave expansion and a single-cut near-field far-field transformation (SCNFFFT). Our system has been successfully applied to the bistatic RCS measurements of a metasurface (100 mm width, 50 mm height, and 0.127 mm thickness) at 60 GHz where two horn antennas are used for the PWS (Tx) and the SCNFFFT (Rx) and placed at the circular distances of 1.735 m and 0.35 m respectively. The peak and pattern errors of the RCS are 0.4 dB and below -25 dB respectively. Using the proposed 2D PWS and SCNFFFT, the compact 2D bistatic RCS measurement system is realized without large equipment such as CATR.
The application of multi-probe (MP) technology in near-field (NF) measurement scenarios is well-known for its ability to significantly reduce test time. This is achieved by electronically sampling the radiated field using different probes in the array, eliminating the need for mechanical probe movement. However, in planar near-field (PNF) measurements, the accuracy is contingent on probe correction (PC) during post-processing. Characterizing the pattern of each individual sensor in a PNF MP system presents an additional challenge, often being impractical or impossible. Previous publications have explored various approaches to address this challenge and achieve an accurate characterization of the MP equivalent pattern. In this paper, we focus on the average probe pattern (APP) technique, which involves the experimental determination of the MP pattern. To validate the effectiveness of the APP technique, we conducted experiments on a large PNF MP system equipped with a 4.65m probe array. Our measurements focused on an electrically large 1.5m diameter reflector antenna (MVG SR150 reflector, fed by a quad-ridge horn) operating in the 1.8–6.0 GHz frequency range. The validation process involved the comparison of MP measurements processed with the APP technique and conventional open-ended waveguide (OEW) PNF measurements. To ensure the reliability of the validation, we conducted the comparative tests within the same frequency range and test setup. This minimized the impact of measurement errors, enabling a robust and accurate comparison between the techniques. By validating the APP technique's effectiveness, we aim to establish its suitability for improving accuracy in PNF MP system measurements.
There are several applications that require the Fourier transformation from data obtained on a regular polar grid to a regular sine-space grid, and one of these is the processing of plane-polar near-field data. The most common approach to this task is to interpolate from the polar grid to an X-Y grid and then use the conventional 2D Fourier transform. This paper revisits an alternative algorithm, referred to herein as the polar-coordinate Fourier transform (PCFT), for doing the same transformation from polar input to a regular sine-space output grid. This PCFT has some advantages when processing data undersampled in their angular phi spacing, and appears to offer the possibility of probe correction without having to counter-rotate the probe. The process of the PCFT is similar to that of the conventional 2D Fourier transform. These two processes are compared. Rather than interpolating the polar data to the X-Y grid, the PCFT starts with a 1D transform along each diametric spoke of the polar wheel. Each spectral output is then rotated by the corresponding phi angle and interpolated to a common sine-space output grid. If probe-pattern correction is needed for a probe with no extra roll axis, then a notional approach is also described.
This paper provides an overview of measurement uncertainties associated with a planar near-field test methodology for measuring typical system level characteristics of transceiver payloads. We describe a framework for analyzing the uncertainties when measuring these system level RF parameters in a near-field range. More specifically, saturating flux density (SFD), equivalent isotropic radiated power (EIRP), gain-to-noise temperature (G/T) and end-to-end gain vs. frequency are addressed. Results from a set of validation measurements, performed on a frequency converting simulated payload are used as baseline. A combination of analysis and direct measurements are presented to validate the measurement methodology for each parameter and estimate corresponding uncertainties. The contribution of this paper is the presentation of these methodologies and establishing an initial set of uncertainty boundaries to qualify the near-field test approach for this purpose.
In 5G O-RAN, a radio unit (RU) is connected to an upper-layer network element through an eCPRI interface, relying on digital modulation for data transmission. Therefore, unlike conventional 4G antenna system verification processes, RU radiation pattern testing in this data transmission mode necessitates novel testing approaches. Moreover, millimeter-wave signals in 5G undergo severe transmission losses and lack effective multipath channel characteristics, leading to poor base station coverages in this frequency range. The reconfigurable intelligent surfaces (RIS), an emerging technology that exploits the channel properties for the dynamic manipulation of the propagation environments, is a promising solution to the abovementioned problem. However, evaluating the effectiveness of the dynamic energy transfer for the RIS is a crucial challenge in the development of this technology. This paper presents the novel configuration based on the combined near-field and bistatic measurement systems at Taiwan Tech for RU and RIS performance verifications. We propose a near field measurement system to verify the radiation pattern of the RU in data transmission operation. Also, we integrate a compact antenna test range (CATR) and the planar near field scanner to form the bistatic measurement system and conduct performance evaluation of the scattering characteristics of the object under test. Those testing approaches can more accurately evaluate, verify, and optimize RF coverages of the network deployment for 5G and beyond.
Sampling of the probe signal first-order spatial derivative, in addition to the probe signal itself, enables the sampling step to be increased to twice that of the standard sampling criterion. In this work, we investigate – theoretically, numerically, and experimentally - the potential of using probe signal derivatives for spherical near-field antenna measurements with the aim of reducing the measurement time. We present a closed-form Fourier coefficient formula and a closed-form interpolation formula based on signal and signal derivative samples. We validate these new formulas using experimental measurement data and thus demonstrate the feasibility of doubling the sampling step in practice. We discuss different principles for determining the probe signal derivative; and we demonstrate the use of probe signal derivatives, in addition to probe signals themselves, for a full-sphere near-field antenna measurement skipping every second full-circle scan.
Spherical Near Field (SNF) measurement systems are
primarily limited in usable bandwidth by the probe frequency
coverage. This limitation mainly arises from the presence of
higher-order azimuthal modes in the probe pattern [1]. In case of
electrically large or offset AUTs, such a limitation may be
overcome by a full probe correction algorithm for the NF/FF
transformation [2]. However, probes approximating first order
performance over the full bandwidth are generally preferred.
Traditionally, first-order probes based on geometrically
symmetric Ortho-Mode Junctions (OMJ) with externally
balanced feeding have been widely accepted. These probe designs
rely on couplers that provide equal amplitude and opposite phase
distribution at their output ports [3]. In this paper, the design
and validation of a novel 3dB/180° coupler is presented. The
concept is based on the natural anti-symmetric properties of the
electric field within the component, providing a quasi-perfect
amplitude and opposite phase distribution. To achieve these
properties, an architecture based on slot coupling is selected. The
design has been implemented in several frequency bands, from
UHF to Ku-band, as stand-alone cased components.
Experimental data at L/S-band is presented in this paper,
showing excellent performance in terms of matching, balance,
and isolation between output ports, well in-line with full-wave
electromagnetic predictions. In addition, the impact of the
coupler accuracy is also assessed on a relevant SNF test case.
This paper introduces an innovative testing system designed for the characterization and calibration of W-band active phased array antennas utilizing antenna-in-package (AiP) technology. The proposed system is a multi-axis scanner with nine degrees of freedom, used to perform near-field and farfield measurements with same setup. The multi-axis system allows precise positioning of the antenna and the probe, allowing accurate measurements of the antenna radiation patterns in both near-field (NF) and far-field (FF) regions. Experimental results show that the proposed hybrid multi-axis scanner significantly improves the calibration accuracy of the antennas on-chip at 77 GHz compared to traditional far-field systems. Using the hybrid scanned (near-field and far-field) provides a versatile and effective test procedure to even characterize additional electromagnetic artifacts that may be present during the test. The proposed system enables accurate calibration and measurements by providing precise control over the positioning of the antenna and probe, while minimizing the effects of interference from the surrounding environment. Excellent agreement between the antenna array pattern measured in the near-field and far-field is achieved post-calibration. Moreover, the suggested system supports both automated and manual calibration, rendering it versatile and adaptable across various applications.
The plane-polar approach for near-field antenna measurements has attracted a great deal of interest in the open literature during the past four decades [1, 2, 3, 4, 5, 6, 7]. The measurement system is formed from the intersection of a linear translation stage and a rotation stage with the combination of the axes enabling the scanning probe to trace out a radial vector in two-dimensions facilitating the acquisition of samples across the surface of a planar disk, typically being tabulated on a set of concentric rings. In its classical form, the probe moves in a fixed radial direction and the AUT rotates axially. However, with the ever more prevalent utilization of industrial multi-axis robots and uninhabited air vehicles (UAV), i.e. drones, being harnessed for the task of mechanical probe positioning, such systems offer the possibility of acquisitions being taken across non-planar surfaces. In this paper an accelerated, rigorous, near-field to far-field transform for data that was sampled using a polar acquisition scheme that is based on a Fourier-Bessel expansion [4] is developed and presented that can be employed in the above circumstances. This highly efficient, robust, transform enables near-field data acquired on planar, and non-planar, surfaces to be transformed to the far-field providing the acquisition surface is rotationally symmetric about some fixed point in the x,y-plane with z being purely a function of the radial displacement. The utility of the non-planar acquisition interval stemming from the ability to minimize truncation effects without needing to increase the measurement size. The transform efficiency stems from the utilization of the fast Fourier transform (FFT) algorithm with the rigor and robustness deriving from the avoidance of recourse to approximation, e.g. piecewise polynomial interpolation cf. [7]. Numerical results are presented and used to verify the accuracy and efficiency of the novel transformation, as well as to confirm convergence of the requisite Bessel series expansion and sampling theorem.
A new far-field valid angle equation for rectilinear planar near-field measurements is presented. The new valid angle equation was derived by viewing the planar near-field to far-field transformation process as generating a set of pseudo plane waves by a synthetic phased array and subjecting the antenna-under-test to the radiation from this synthetic array. The synthetic phased array does not physically exist; rather, the array is formed during the post-processing of the planar near-field measurements. As part of this discussion, we present results from a numerical model, illustrating the total electric field present in the test zone due to the finite extent of the synthetic phased array. The new far-field valid angle equation accounts for the diffraction effects of the finite-sized synthetic array, and uses the industry accepted test-zone magnitude ripple of +/- 0.5 dB to limit the valid far-field angle for a fixed scan plane size. The resultant valid far-field angle computed with the new equation is compared against previously established and popularly accepted valid angle equations, such as the equations previously presented by Yaghjian, Maisto, and Joy [1, 2, 3]. Brief discussionsare offered on the measurement of low directivity antennas with a planar near-field measurement system, and on amplitude tapering of the near-field measurements to improve the quality of the pseudo plane wave. REFERENCES: [1] A. D. Yaghjian, "Upper-bound errors in far-field antenna parameters determined from planar near-field measurements, part 1: analysis," National Bureau of Standards (NBS), Boulder, Colorado, USA, vol. Technical Note 667, no. October 1975. [2] M. Maisto, R. Solimene and R. Pierri, "Valid angle criterion and radiation pattern estimation via singular value decomposition for planar scanning," IET Microwaves, Antennas & Propagation, vol. 13, no. 13, pp. 2342-2348, 2019. [3] E. B. Joy, C. A. Rose, A. H. Tonning, and EE6254 Students, “Test-zone Field Quality in Planar Near-field Measurements,” in Proceedings of the 17th Annual Meeting and Symposium of the Antenna Measurement Techniques Association, Williamsburg, 1995.
Our work proposes a novel method for obtaining full-sphere radiation patterns from truncated measurements. This is achieved by stitching partially overlapping truncated field patterns, which together cover the whole measurement sphere. Measuring an antenna in different orientations results in a misalignment between the measurements which is not perfectly known and needs to be accounted for in order to stitch the patterns together. Our method first makes use of an iterative procedure to compute spherical wave coefficients capable of accurately describing the truncated patterns. Recent investigation of properties of radiation patterns from iteratively obtained spherical wave coefficients under rotation and translation has shown that, while coordinate system manipulation introduces additional errors, these errors are contained predominantly in the region near the angle of truncation. They are thus negligible if a sufficient overlap between the truncated patterns exists. To align truncated patterns, a bounded minimization of the normalized mean squared error in the overlapping range between patterns is done, varying through a range of different translation and rotation vectors for one truncated pattern while keeping the other pattern fixed. Finally, the fixed and the optimally aligned patterns can be stitched together. The proposed method was validated on spherical wave coefficients (SWCs)-based models and EM simulation models for randomly chosen misalignment offsets. For the SWCs-based models, the normalized mean squared error (NMSE) after pattern stitching was found to be below -53 dB for all tested misalignment offsets. Similar results were observed in the case of EM simulation models as well, where the error was found to be below -52 dB for all tested misalignment offsets. In the final validation step, the method was tested on actual measurement results of two low-gain antennas. For each of the validation steps, potential sources of error are identified. The method demonstrates promising results in achieving full-sphere characterization of low-gain antennas in typical non-full-sphere measurement chambers.
This paper introduces a single-cut near-field measurement technique using only-amplitude data. The technique is based on measuring the near-field amplitude of an antenna over a ring, i.e. phi=0 cut, and performing a far-field transformation to obtain the radiation pattern over the same ring. This avoids the need of a full near-field spherical measurement if one is interested in only a few cuts of the far-field pattern. The lack of phase information complicates the field transformation. A common approach to solve this issue is to perform two near-field scans a different antenna-probe distance. This has the drawback of doubling the measurement time with respect to a complex measurement and a translation stage is required, which may be infeasible in some antenna measurement facilities. The technique proposed on this paper can retrieve the phase without measuring the near-field in two rings. Instead, the field is measured in one ring using a specialized probe. This probe provides partial coherence information between measurement samples, which can be exploited in a non-convex minimization solver to retrieve the phase of the near field with high convergence guarantee. The specialized probe can be implemented by using two separate probes connected two a dual channel Software Defined Radio (SDR) unit, so that the relative phase between measurement samples is known. Theoretical background of the proposed technique will be disclosed on the paper, along with simulated and measured transformation examples to demonstrate the potential capabilities: -Very fast near-field measurements (only one ring is measured instead of the full sphere). -Only amplitude information is required (no need of maintain stable phase reference, suitable for OTA testing). -No double-scan is required to retrieve the phase (measurement time reduced by half, no need for translation stage). -High reliability: Partial coherence provides a significant amount of independent information to the phase retrieval algorithm.
Abstract— A 2021 AMTA paper[1] introduced a 3D holographic filtering algorithm optimized for the planar near-field (PNF) geometry. This filter has been shown to have an excellent combination of AUT-signal preservation, stray-signal rejection, and processing speed. It requires only the sampling of a conventional PNF measurement, along with a specified 3D boundary surrounding all of the AUT’s possible radiating sources. The 2021 paper[1] suggested some topics for further investigation, specifically the optimal Z spacing through the 3D hologram and the X- and Y-widths of the blanking window’s tapered extension, and those are investigated here. This paper also explores the combination of filtering and probe correction, since the measured convolution of probe and AUT spatial distributions will be wider than that of the AUT by itself. Finally, additional comparisons are made to the more traditional spherical-mode-truncation approach with different synthesized constellations of stray-signal radiators. Keywords: modal filtering, spatial filtering, holographic filtering, stray signals, planar near field [1] S.T. McBride, P.N. Betjes, “Holographic PNF filtering based on known volumetric AUT bounds,” AMTA 2021, Daytona Beach, FL.
During the last few years, the increasing use of wireless equipment has raised the quantity of radiation energy to which human bodies are exposed. For this motivation, an evaluation of the Specific Absorption Rate (SAR) for persons is fundamental to determine the amount of radiation that human tissue absorbs and to comply with human safety regulations. Standard testing methodology consists of measurements with robot-based scalar/vector near-field probes and post-processing. The probe acquires the field level inside a phantom filled with liquid to ensure compliancy with certification standards. Although accurate, this technique could be extremely time-consuming, especially with the arrival of new frequency bands, new standards (5G, Wi-Fi 7), and the requirement to test different beams directions for beam-forming MIMO configuration. Another testing methodology, used especially for pre-assessment, consists of a full simulation of the radiator in the presence of the phantom, but this implies that the full wave model of the device is available, and this is rarely the case. To overcome the above-mentioned limitations, an alternative technique presented in this paper can be applied. This is based on a standalone measurement of the radiating device, that is post-processed with the method of the equivalent currents to generate NF source (in the form of a Huygens box). The SAR values inside the phantom are assessed using a non-invasive procedure with the assistance of a numerical simulation tool. Such method represents a fast procedure for pre-analysis of device prototypes, allowing to perform the conclusive testing only on the final device to verify the compliance with the regulations. The methodology is here experimentally validated on a dipole radiating in a presence of a phantom model by comparison of numerical simulated data and a reference measured data by a MVG ComoSAR V5 system.
Base station antennas for mobile communications (BTS) emit high levels of electromagnetic radiation in their vicinity. These antennas are usually located on the top of a building, and it is critical to determine those areas where the total power density surpasses the levels dictated by the regulators of the corresponding country. This estimation allows mobile operators to optimize the performance of the cellular network while keeping safe EM emission levels in occupational and public areas. The power density on a given region depends not only on the total radiated power but also the radiation pattern of the antenna and the influence of the environment. As a result, antenna measurements become useful to perform these calculations. This paper presents a simulation tool which computes EMF exposure values of BTS antennas considering the influence of the building roof. The tool uses analytical calculations to obtain a fast evaluation of the fields radiated by all the antennas of a given cell site. The calculations are performed considering the radiation of the antenna as a contribution of three different propagation phenomena: a free space direct radiation component, a reflected component due to the presence of the ground and a diffracted field due to the roof corners. Both direct and reflected rays are computed using the Spherical Wave Expansion (SWE) of the BS antenna assuming PEC boundary. The diffracted ray is computed using ITU 526-8 recommendation. The proposed software requires a measurement of the BTS antenna radiation pattern in anechoic chamber. Spherical near-field measurements are proposed to retrieve all antenna parameters needed for the calculations (SWE, efficiency, electrical steering configurations). Full details of all performed calculations will be disclosed on the paper, as well as some simulation examples with measurement data of real antennas to demonstrate its capability and computational efficiency.
This paper presents a selection guide for metal mesh based on shielding effectiveness and optical visibility requirements. Concepts of mesh sizing, wire diameter, metal type, opening size, metal color, and mesh patterning are discussed. The guide provides a detailed explanation of factors that contribute to the shielding performance and optical transparency of various mesh options. Metal mesh has a range of applications in the microwave, antenna, and EMC industries as they are particularly suited for protecting chamber viewing windows. Shielding effectiveness performance is dependent on the mesh sizing, wire diameter, and opening size, where the dimensions of the apertures directly influence the suitability of the mesh for a given frequency range. Finer mesh yields superior shielding, but with limited optical visibility. For this reason, the necessity for finding an optimal tradeoff between shielding performance and optical properties arises, where the selection guide in this paper can be used to make an informed decision. For ideal optical properties, the mesh sizing is critical since it determines the visibility through the material. Mesh layering and alternative optically transparent shielding solutions like RF film are also compared. Although layering of metal mesh offers additional shielding, the layering is associated with a reduction in visibility due to the mesh density and patterning from the Moiré effect. Alternatives like RF film can offer highly transparent solutions, but with inferior shielding effectiveness than metal mesh. This paper provides a quantitative analysis of shielding effectiveness results based on mesh parameters and aperture dimensions. The appropriate frequency ranges for the various metal meshes are also calculated. Using the selection guide presented in this paper, the user is enabled to make an educated technical decision on the metal mesh best suited to satisfy the shielding effectiveness and optical visibility requirements for the application.
Motivation and background: Wireless communications are key for connected and automated driving. Beyond automation levels that require the presence of a driver, tele-operated driving has been receiving more attention recently. For such applications, gapless wireless coverage and stable connectivity are required, enabling a reliable exchange of data like control information or high-definition maps even under poor radio wave propagation conditions. Therefore, extensive testing of the link stability of mobile wireless communication systems is necessary, especially in challenging scenarios that are susceptible to link failure. Objectives and methods: We propose the emulation of relevant corner-case scenarios for virtual-drive testing, consistently and reproducibly derived from field-operational tests on public roads. The available data rate of a LTE link near mobile cell edges is considered a relevant test metric, since the link is expected to be particularly susceptible to failure under such conditions. We performed field-operational tests on two different test tracks, in order to prove the reproducibility and consistency of the proposed case. We have emulated the scenarios in a wired setup under realistic conditions using a communication tester and an interference generator. Power-related key-performance indicators like RSRP and SINR as well as the achievable throughput were systematically studied under laboratory conditions. Results and conclusions: The region around cell edges could undoubtedly be identified as a challenging scenario for automotive LTE communications, leading to a reduction of the data throughput by a factor of 5, on average, compared to the maximum data rate during a test run. This effect could be consistently observed on both test tracks. The emulation of wireless link parameters in such corner-cases reproduced the physical parameters of the field-operational test results very well. Changes of the data rate could be associated with the channel quality indicator. Approaches to improve the emulation of the drive tests is in the focus of future work. However, given the simplicity of the test setup, it represents a sound basis for refined over-the-air tests.