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To verify the proper working of a Reconfigurable Intelligent Surface (RIS), similar to antenna radiation patterns, the RIS reflection pattern has been established as key performance indicator. To overcome the necessity of a bistatic RIS qualification setup, where two antennas at different positions are used, this paper presents a novel measurement approach to obtain the RIS reflection pattern based on a monostatic indirect Far-Field (FF) Compact Antenna Test Range (CATR) setup. Due to the monostatic principle, only one antenna, which is used for transmission and reception, is required. Subsequently, the mono- static reflection patterns are transformed into bistatic reflection patterns by applying different Monostatic to Bistatic Equivalence Theorems (MBETs) known from radar-cross-section theory. With that, the required setup can be simplified in terms of mechanical complexity, setup footprint and the number of measurement scenarios, since incident and reflection angle correspond in the monostatic case. This paper analyzes three different MBETs, namely Kell, Crispin/Siegel and Falconer, with respect to their suitability for RIS reflection pattern measurements. Moreover, a monostatic CATR test environment is presented and two metal plate based RIS calibration approaches are introduced. This novel monostatic RIS measurement approach is validated with simulation and measurement data of two mmWave fixed beam RISs. Both of them are reflecting an impinging signal from broadside (θ = 0°) direction into 47° at a center frequency of 27GHz. The results prove the suitability of this approach.
This paper presents research validating the conductive resonant sphere creeping wave phase dilation discovered in high-resolution imaging presented at the 2023 Antenna Measurement and Techniques Association (AMTA), which focused on using a small resonant sphere as a test probe for assessing Radar Cross Section measurement accuracy [1]. The associated analysis uncovered a discrepancy in the creeping wave Standard Model physical pathlength around the sphere having less phase than required for resonance. This paper presents a new creeping wave phase dilation model resolving the phase difference and validating results with computational electromagnetic field predictions.
Tapered anechoic ranges were introduced in the late 1960s. Since their introduction tapered anechoic chambers have become popular tools for the measurement of antenna patterns at frequencies under 1 GHz. Dating back to their first installations, several papers mention the fact that these chambers did not have a spherical wave propagation and thus, the Friis transmission equation to measure gain cannot be applied [1,2]. The array factor theory of taper chambers presented in [3] states that from the point of view of the antenna in the QZ the tapered chamber appears to be a free space environment. The phase behavior across the QZ, reported in [4] appears to agree with the theory since the phase distribution follows the far field equation. In this paper simulations for a dipole and a biconical antenna are performed that suggest that the array factor theory for the tapered ranges while not perfect provides an approximated explanation for their operation. The simulations confirm the measurements done in [2] and additionally show that at some discrete frequencies the propagation in the tapered range does follow closely the free space attenuation.
This paper presents an overview of the induced ripples observed in the far-field antenna patterns of the Antenna Under Test (AUT) when measured with an open-ended waveguide antenna probe in a near-field planar system. The author hypothesized that induced ripples in far-field patterns are primarily originated by diffracted fields on the ground plane that supports the collar absorber. This study systematically evaluates the effects of absorber size and quality. Numerical simulations and experimental measurements are employed to validate the author’s hypothesis, providing insights into the relationships between these parameters and their influence on the induced ripples in far-field patterns. Results indicate that collar absorbers with reflectivity better than -30 dB are optimal for achieving accurate element characterization of phased array antennas.
The standard Near-Field antenna characterization allows to reconstruct the Far-Field pattern over the whole visible domain, even if, in many cases, the partial characterization of the Far-Field pattern just along some cuts can be sufficient, and becomes preferred if realized in shorter measurement time with respect to the standard case. A method for Partial Characterization has been proposed. The approach provides a general framework and defines the optimal distribution of the near-field samples required to reconstruct the Far-Field pattern along the cut of interest. The main features of the method are presented, and the performance is verified, experimentally, for two test cases.
Phaseless spherical near-field antenna measurements generally address the challenge of computing complex coefficients describing the antenna under test’s (AUT) radiation behavior from amplitude near-field measurements. The AUT’s far-field (FF) can then be obtained from those complex coefficients. Most of the techniques used in the literature result in a modified sampling method (e.g., two-spheres or sphere with two probes) and a phase retrieval algorithm (e.g., WirtingerFlow or PhaseLift). Sampling methods are chosen to increase the number of independent measurements to aid phase recovery. In our contribution, we introduce the approach of random masks, leaning on the concept of diffraction patterns, which is well-known and used in the phase retrieval theory. Random masks can be seen as intentional random perturbations occurring in the measurements either at the AUT, probe or in between; or as an extension to conventional measurements to increase the number of independent measurements. State-of-the-art phaseless sampling methods can also be interpreted as masks with limited randomness. A general mathematical model is presented, and different types of masks based on random distributions are investigated through simulations on a transformation with spherical wave expansion. Firstly, generic masks are considered to benchmark the achievable reconstruction error, and secondly, masks based on probes are examined.
We address the generation of complex near-field (NF) wavefronts through a two-step process involving the determination of an equivalent radiating panel and its practical implementation as an array. Our novel approach discretizes 2D radiating panels using an optimized, nonuniform 2D quadrature rule. The optimized quadrature nodes determine the array element locations, while the excitation coefficients are obtained using the Singular Value Decomposition (SVD). Numerical results demonstrate the effectiveness of the method in accurately generating NF waveforms.
This is a continuation of the work presented at the AMTA 2022 symposium to assess the accuracy of on-axis antenna gain with commercially available computational electromagnetic (CEM) solvers [1]. Common practice for computing antenna gain normalization via the gain-transfer technique is to use the on-axis NRL gain curve of a pyramidal standard gain horn (SGH) derived by Schelkunoff and Slayton [2], [3]. Due to approximations in this formulation, Slayton assessed an uncertainty of ±0.3 dB for typical SGHs operating above 2.6 GHz. Since this uncertainty term is often one of the largest terms in the range measurement uncertainty budget for AUT gain, it is highly desirable to reduce it. Many studies in the past have attempted to improve upon Slayton’s expressions for SGH gain, but none have achieved widespread use. The previous investigation demonstrated the use of several commercially available solvers, including HFSSTM, CST Studio Suite®, and FEKO® to model the on-axis directivity and gain of a commercial off-the-shelf (COTS) X-band SGH [1]. In that work, the CEM simulation results from multiple solvers in HFSSTM, CST Studio Suite®, and FEKO® are shown to be within ±0.0075 dB of each other. This work is an extension to study how closely the simulation models match recent measurements of gain for the same MVG SGH820 horn discussed in previous paper. These measured and modeled results are compared with the international intercomparison results of a similar SGH [4], in conjunction with a best-estimated simulation model of the original dimensions from [4]. To capture the differences of the physical as-built antenna versus the simulation model, a simple tolerance study in simulation is performed based on the build tolerances of the antenna to provide an uncertainty estimate of the simulation results.
One of the major contributions to the measurement uncertainty of antenna measurements are multiple reflections between antenna under test (AUT) and probe antenna. In the case of spherical near-field (SNF) measurements, multiple reflections are typically estimated and compensated for by conducting full SNF measurements at different radii and averaging the transformed far-field results. However, the need for several measurements leads to a multiplication of the measurement duration, and subsequently to an increase in costs. Another option is to increase the measurement radius, which might not be possible depending on the positioning equipment. Therefore, a technique to reduce multiple reflections between AUT and probe antenna by intentionally tilting the latter is presented. The technique is evaluated with a robotic antenna measurement system, the flexibility of which allows to almost arbitrarily tilt the probe antenna and perform a spherical measurement in this tilted configuration. It is shown that the magnitude of the reflections can be reduced significantly with this approach, even for small tilt angles. A comparison with the conventional averaging technique indicates that the presented approach reduces the error to a similar level, but at a fraction of the measurement time.
Classic methods for extracting material characteristics typically demand rigorous calibration, multiple samples, precise location measurements, etc. A recent research effort led by Zhao Caijun, Jiang Quanxing, and Jing Shenhui utilized a simple transmission/reflection method to extract high accuracy permittivity results from a Coaxial Line system. This method uses two uncalibrated scattering parameter measurements: one of the empty fixture and one of the sample at a single position. This paper extends the method to produce accurate permittivity results from a Rectangular Waveguide system once corrected for detector mismatch.
Transceiver satellites with a ”bent-pipe” payload are commonly used in communication systems. Accuracy of measurement of their main End-to-End (E2E) parameters, such as Saturating Flux Density (SFD), Gain flatness (G/F), Equivalent Isotropic Radiated Power (EIRP) and Gain over Temperature (G/T) depends not only on the test setup, but also on the accessibility of different test points in the payload. In this work, we focus on the error budget for different accessibility levels when the payload is tested in Planar Near-Field (PNF).
The extrapolation method is widely used for antenna absolute far field gain calibration. The technique involves measuring responses between precisely aligned antenna pairs across varying distances. Previous studies have suggested that how one measures the separation distance—whether from aperture face to face or from phase center to phase center—doesn't influence the resulting far-field gain. However, our present study demonstrates that this assumption is incorrect. The choice of reference points for measuring separation distance can indeed impact the computed far-field gains. Our investigation shows that using the distance from the phase centers provides the most accurate far-field gain. Through numerical experiments and measurement data, we illustrate the discrepancies in the far-field gains caused by different distance definitions. Since the phase center of the antenna under test is usually unknown in practice, finding the phase center separation distances to apply to the extrapolation calculation isn't straightforward. To address this, we introduce a novel searching algorithm that varies an offset distance during polynomial fitting. This generates various convergence curves with different trends and rates, allowing for the accurate determination of phase center separation distances. The proposed algorithm not only enhances the accuracy of the antenna gain extrapolation method but also provides the phase center information of the antenna under test, all without requiring additional measurements.
This paper presents a novel design for a multi-probe antenna array for continuous measurement in a planar near- field system. This design reduces scanning time while maintaining accuracy compared to conventional methods used in near-field planar systems. The work introduces the design of the irregular probe array and discusses its trade-offs and functionality. It includes a comparison of the results from the two methods mentioned and analyzes the time durations associated with each approach. Additionally, the paper provides projections based on previous data to estimate scan durations for a large number of sampling points, considering the impact of the velocity of the linear positioners.
The IEEE Antennas and Propagation Standards Committee (APS/SC), sponsored by the IEEE Antennas and Propagation Society (AP-S), is currently developing a recommended practice tailored for the modeling and simulation of antennas (IEEE P2816). Different numerical modeling techniques such as the finite element method (FEM), integral methods e.g. method of moments (MoM), the finite difference time domain (FDTD) method and the transmission line matrix (TLM) method are described. In addition, benchmark problems are also considered to ease the use of the recommended practice. For example, the biconical antenna is proposed as a benchmark problem for the numerical simulations using the above methods. Several international laboratories have already performed the numerical simulations of this biconical antenna. To confront the theoretical and numerical results with measurements, the same biconical antenna was proposed for fabrication and inter-laboratory measurement campaign. Herein, the fabrication and initial measurements of the prototype are discussed. An important difference between the theoretical, simulated and fabricated antenna is the feeding point. In theory, it is considered infinitely small whereas in the proposed numerical model, the gap in-between the two cones is assumed to be 0.3 mm. In practice, such a small gap cannot be enforced during the fabrication process. Since the off-the-shelf available SMA connector has a minimum diameter of 0.7 mm, the minimum diameters of the central and outer conductors of the 50W feed-line (Teflon filled) section were kept at 1 mm and 3.34 mm, respectively. In the actual fabrication, only a gap of 4 mm could be achieved in-between the two cones. An external quarter-wave skirt is further used as a balun for reasonable impedance matching. A Rohacell section is used to hold the arms of the antenna which are heavier. The realized prototype, therefore, differs significantly at the feeding point. The relevant simulation and experimental results are presented.
The ESA HERA-JUVENTAS mission relies on 50-70MHz dipole antennas mounted on a cubesat [1]. The mission requires an accurate verification of the radiation properties of the whole antenna system including the matching and amplification boards. The performance verification of low gain antenna systems below 400MHz is a challenging task because of the reflectivity of the measurement environments. Spherical Near-Field (SNF) measurements are the most suitable approach for such Devices Under Test (DUT) [2] but require a sufficiently large anechoic chamber equipped with absorbers able to provide low reflectivity. Meeting these requirements at low frequencies is often too expensive, as for the case of the HERA-JUVENTAS antenna system verification. An outdoor testing solution could be an alternative but at the expenses of measurement accuracy and repeatability. The SNF system installed in the HERTZ testing facility at ESA-ESTEC has been selected as cost-effective solution for the verification of the HERA-JUVENTAS cubesat. The HERTZ anechoic chamber was originally designed for measurements down to 400 MHz, hence, due to limited electrical size (~5λx2λx2.5λ) and poor absorption provided by the treatment of the chamber walls (~2dB), a high reflective environment is expected at 60MHz. The so-called Synthetic Probe Array (SPA) technique is a very effective solution to significantly improve the measurement accuracy in case of reflective environments. With the SPA technique each sample point on the NF sphere is measured with several probe positions generating a “virtual” array able to properly shape the equivalent probe radiation pattern, minimizing the illumination of the chamber walls. Validation of the SPA technique, combined with the λ/4-averaging technique to also minimize the effect of the backwall of the DUT, have been recently performed by means of simulations and scaled measurements as presented in [3]-[4]. In this paper the actual measurement results of the HERA-JUVENTAS cubesat performed in HERTZ with the SPA and λ/4-averaging techniques will be presented for the first time. Comparisons in terms of radiation pattern and gain, with the conventional single probe SNF approach will be shown to highlight the effect of the measurement environment at 60MHz and the improvements obtained with the considered techniques.
Measurements of modern multi-service antenna systems require ever increasing bandwidths of the measurement equipment. The main bandwidth limiting factor of traditional Spherical Near Field (SNF) systems is mainly the probe as it should radiate only first-order azimuthal spherical modes to apply the first-order Probe Compensation (PC). Even though full PC techniques are becoming standard, enabling the use wideband antennas with more than 10:1 bandwidth as probes, high-purity first-order probes are still required in many applications, because of the simplification of data processing and calibration. Conventional dual-polarized first-order probes are based on Ortho-Mode Junctions (OMJ) with externally balanced feeding. The OMJ is fully symmetrical using two pairs of excitation pins fed by high precision 3dB, 0º/180º hybrid couplers to achieve good matching and maximize the cx-polar performance. Unfortunately, realistic couplers provide some excitation errors which are one of the main contributors of the generation of unwanted higher order spherical modes. Even a small unbalancing in amplitude or phase of the coupler will excite higher order modes at frequencies where these modes are allowed to propagate. Beside the possibility to compensate the effect of the higher-order modes in post-processing (e.g. full PC), the propagation of the spurious spherical modes can be controlled directly on the probe with improved designs of the feeding mechanism or considering ad-hoc designed hybrid couplers. In this paper, two innovative and high performance SNF probes will be presented. Both probes are based on an inverted quad-ridge waveguide technology. An advanced feeding mechanism allows the first probe to provide a high modal purity in the 617-960 MHz band, rejecting errors introduced by the external coupler. In the second one, a highly accurate coupler has been designed to minimize the higher order modes on a large bandwidth, 1427-4200 MHz. The two probes have been designed as part of the upgrade of a gantry arm system used to test modern base station antennas. The same measurement system has been used to calibrate the two probes and to verify the expected performance both in terms of radiation pattern and spherical modal content. The achieved measurement results will be shown in this paper.
The dropped-channel polarimetric synthetic aperture radar (PolSAR) compressed sensing (CS) model [1,2] is able to recover an unmeasured polarimetric channel by utilizing antenna crosstalk and compressed sensing techniques. For successful recovery of a dropped channel, a sufficient amount of crosstalk is required to mix the information from the dropped channel into the measured channels. Recently, Monte Carlo simulations were conducted on the dropped-channel PolSAR CS model, and a range of crosstalk values of -9 dB to -3 dB was found to produce low recovery error for a variety of SAR image point spread functions and scene sparsity levels [3]. However, dual-polarized antennas are typically designed to have very high channel isolation, with crosstalk much less than the – dB minimum desirable value. To lend credibility to the dropped-channel PolSAR CS model, a new antenna is needed that can provide such high amounts of crosstalk without sacrificing gain, bandwidth, and radiation pattern. In this paper, we design a new, high crosstalk, dual-polarized patch antenna, using Ansys/HFSS to optimize pin placement and patch size for the desired gain, center frequency, and crosstalk values. The designed antenna is constructed, and S-parameters, gain, and radiation patterns are measured. The measured crosstalk values are then tested in the dropped-channel PolSAR CS model over a few deterministic scenes, demonstrating sufficient expected performance of the physical antenna for sparse scene recovery. 1. J. A. Jackson and F. A. Lee-Elkin, “System, Method, and Apparatus for Recovering Polarization Radar Data," United States of America Patent US11 194 104B1, Dec., 202 2. J. A. Jackson and F. A. Lee-Elkin, “Exploiting Channel Crosstalk for Polarimetric SAR Compressive Sensing," IEEE Transactions on Aerospace and Electronic Systems, vol. 56, no. 1, pp. 475-485, Feb. 2020. 3. J. Becker, Theory and Design of a Highly Compressed Dropped-Channel Polarimetric Synthetic Aperture Radar, PhD Dissertation, Air Force Institute of Technology, June 2022.
Direct far-field (DFF) testing has become the baseline test methodology for sub-6 GHz over the air (OTA) testing of the physical layer of radio access networks (RAN). However, the proliferation of mm-wave massive multiple input multiple output (Massive MIMO) antennas for 5G New Radio (NR) rollout and the use of complex waveforms for communication system testing and primary Figure of Merit (FoM) determination has necessitated the adoption of the Compact Antenna Test Range (CATR) as the preferred test solution. The CATR was initially conceived as comprising an efficient way of testing electrically large antennas at very much reduced, fixed, range lengths [1]. However, early workers quickly recognized that the reflector edge treatment and chamber wall illumination are significant factors determining the quality and purity of the collimated pseudo plane-wave with this becoming especially important at mm-wave frequencies [3]. Using modern powerful digital computational simulation techniques [2] in combination with genetic optimization, the edge treatment can be evolved for a specific CATR application as part of the design process for a range of reflector edge treatments [3, 4]. This paper extends the authors previous work to present a novel approach for the reflector edge treatments than have hitherto been considered within the design and genetic optimization procedure, while also taking into account both wall illumination and direct quiet-zone illumination. Resulting quiet-zone performances are compared and contrasted. [1] C.G. Parini, S.F. Gregson, J. McCormick, D. Janse van Rensburg “Theory and Practice of Modern Antenna Range Measurements”, IET Press, 2014, ISBN 978-1-84919-560-7. [2] S.F. Gregson, C.G. Parini, “Examination of the Effect of Common CATR Quiet Zone Specifications on Antenna Pattern Measurement Uncertainties”, Loughborough Conference on Antennas and Propagation, Loughborough, November 2017. [3] M. Dirix, S.F. Gregson, “Optimisation of the Serration Outline Shape of a Single Offset-Fed Compact Antenna Test Range Reflector Using A Genetic Evolution of the Superformula”, EuCAP virtual conference, March 22-26 2021. [4] M. Dirix, S. Gregson and R. Dubrovka, “Genetic Evolution of the Reflector Edge Treatment of a Single Offset-Fed Compact Antenna Test Range for 5G New Radio Applications,” in AMTA Annual Meeting and Symposium, Daytona Beach, Florida, 2021
Robot-based measurement systems offer a high number of degrees of freedom for the configuration of the targeted antenna measurement. Especially in comparison to the conventional planar, cylindrical or spherical measurement chambers, complex measurement sequences can be exploited. In addition, the actual measurement path is not decisive for an antenna measurement since the data is acquired only at discrete sampling positions. Spline-based measurement trajectories provide a way to obtain the measurement data at the intended positions without specifying a fixed path. Instead, it is up to the robot controller itself to calculate and optimize the path between the various spline support points, for example regarding the greatest path speed. However, further optimization potential can be accessed by reducing the number of path-defining spline support points and instead recording the measurement data on the resulting path. This sampling data is thus not on a regular or uniform sampling grid, but on the path optimized by the robot controller, both in terms of position and orientation. Accordingly, a pointwise probe correction is essential so that the actual position and orientation of the probe can be considered in the calculation of the spherical mode coefficients. In order to evaluate the radiation pattern transformed into the far field of the antenna under test as well as the required measurement time, the spline-based measurements are compared to a conventional spherical measurement as usually performed with roll-over-azimuth positioners. The results show that spline-based motion sequences enable faster antenna measurements, since the actual trajectory is no longer predetermined, but can be optimized by the robot controller itself for the underlying measurement setup.
Currently to determine the basic parameters of shales, namely Maturity (which indicates production potential), geochemical analysis need to be performed. These analyses may take days to weeks, depending on laboratory availability. Moreover, by the time the samples get to the laboratory, they could be damaged or poorly preserved, thus creating a significant source of uncertainty in the measurements. Pyrolysis is a method that introduces a sample of rock, of known mass, into a sealed oven that is programmed to heat the sample according to a prescribed rate of increasing temperatures that terminates at 650°C. During the initial heating, upon reaching a threshold in temperature somewhere around 300-350°C, a significant amount of hydrogen is recorded which is called the “S1” peak. With further increases in temperature beyond 350°C, another threshhold is reached at 550-600°C, where yet more hydrogen is evolved from the rock and the peak recorded at that stage is called “S2”. A microwave heating and testing for geological applications was tested with different shale samples. The system consists of a dual-mode microwave cavity, where heating and measuring is performed simultaneously with two different microwave sources. The cavity has a diameter of 104.92 mm and a height of 85 mm. A small shale sample of 9.8 mm diameter by 15 mm height is introduced in a quartz vial with an inner diameter of 9.8 mm and 120 mm. Depending on the electrical losses, the sample could be heated up to 1200°C. Initial complex permittivity measurements show that the imaginary part exhibits relaxation processes at specific temperatures. These temperatures coincide with the expected temperatures of the S1 and S2 peaks of the pyrolysis method, from which we can compute the vitrinite reflectance of the sample, which is an indicator of Maturity. Thus, allowing for quick estimates of maturity, which allows for real time decisions on the development of unconventional resources.