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Open Source Antenna Pattern Measurement System
An open-source antenna pattern measurement system comprised of software-defined radios (SDRs), standard PVC tubing, and 3-D printer hardware will measure the radiation patterns of student-built prototype antennas. The antenna pattern measurement system developed at Weber State University (WSU) was inspired by the published work of Picco and Martin . Their low-cost and practical system utilized commercially-available 2.4 GHz wireless routers. Open-source firmware was loaded on the routers to access the received signal strength indicator (RSSI) data. The RSSI was recorded versus antenna-under-test orientation using National Instruments LabVIEW. The WSU antenna pattern measurement prototype utilizes wideband software-defined-radios to generate, transmit, and receive the test signal. Synchronous belts, gears, and 3-D printer parts were chosen and designed to address mechanical problems described by Picco and Martin. Position control is achieved using an Arduino microcontroller with open-source software developed for 3-D printer systems. Measured principal plane gain patterns for three antenna prototypes are compared to simulated results. Models were constructed using commercial Method-of-Moments (FEKO) for comparison. Measured Radiation pattern data was scaled to the simulated Gain values for a quarter-wave monopole over a finite ground plane, a Yagi-Uda directional antenna, and an air-backed circular microstrip patch antenna. The low-cost, open-source nature of the measurement system is ideal for undergraduate-level investigation of antenna theory and measurement. It is anticipated the SDRs will permit future research of modulation methods and encoding to improve measurements in non-anechoic environments.
Polyhedral Sampling Structures for Phaseless Spherical Near-Field Antenna Measurements
In conventional Spherical Near-Field (SNF) antenna measurements, both amplitude and phase are necessary to obtain the Far Field (FF) of the Antenna Under Test (AUT) from the Near-Field (NF) measurements. However, phase measurements imply the use of expensive equipment, e.g., network analyzer, and rely on the assumption of having access to the reference phase, which is, for example, not the case in Over The Air (OTA) measurement scenarios. For these reasons, phaseless approaches gain attention and different methods have been investigated such as two-sphere techniques, indirect holography, or the use of different probes. Recent research on two-sphere techniques introduces algorithms originally developed for solving the so-called phase retrieval problem like PhaseLift or Wirtinger-Flow. Applied to SNF, the phase retrieval problem corresponds to obtaining the phase of the Spherical Mode Coefficients (SMCs) from amplitude NF measurements only. It has been shown that Wirtinger-Flow benefits from taking measurements over different structures, decreasing the redundancy. First investigations examined the combination of two spheres resp. a sphere and a plane and showed better reconstruction of the FF with the second combination. Furthermore, it has been shown that increasing the distance between both structures improves the reconstruction of the FF. Note that so far investigations have been based on the plane wave expansion. We currently deepen the knowledge presented above in a framework solely based on the spherical wave expansion. From a mathematical point of view, planes can be seen as spheres of infinite radius, i.e., a plane combined with a sphere may be interpreted as a special case of combining two spheres. This interpretation goes hand in hand with the observation that an increased radius difference between both spheres leads to better reconstruction performance. Consequently, we analyze different polyhedral sampling structures composed of planes (such as tetrahedrons or cubes), mimicking several spheres of infinite radius in different spatial directions. For the mathematical analysis of non-spherical structures in the basis of spherical waves, pointwise probe correction is used. First experiments show a better reconstruction of the FF compared to the standard two-spheres/sphere-plane sampling.
A Validated Model for Non-Line-of-Sight V2X Communications
As vehicle autonomy and active safety features become more advanced and ubiquitous, it becomes clear that vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication, together under the umbrella of vehicle-to everything (V2X), can help to enable these autonomous and active safety features by providing useful sensing and localized network capabilities. One problem facing the development of such communication networks is the difficulty involved in accurately predicting the key performance indicators (KPIs) associated with it - e.g., packet error rate (PER) and received signal strength indicator (RSSI) - for an arbitrary setup of antennas and occluders. In this paper we will present a model for V2X communications using a commercial simulation software, Altair's FEKO and WinProp suites, for predicting electromagnetic field intensity at microwave frequencies under different scenarios of antenna placement and occluder setup. We will also validate this model against field data collected using Cellular V2X (C-V2X) radios. We considered three distinct non-line-of-sight (NLOS) scenarios involving a pair of vehicles operating a CV2X inter-vehicle communication channel: 1. A stationary vehicle located directly behind a shipping container and a moving vehicle performing loops around it. 2. So-called urban canyon with tall metal walls on either side of the moving vehicle for a portion of its loop around the stationary vehicle. 3. Fully-covered tunnel, where both vehicles are moving, one leading the other around a loop and through a tunnel. We will discuss the simulations of these three scenarios in light of real-world data taken from field tests of identical scenarios, for the dual purposes of validating the simulation model against real-word data, and developing a model to predict the PER and RSSI at any theoretical receiver location. Together, these will allow us to perform a simulation for any arbitrary potential (NLOS) scenario and get an estimate of the channel PER and RSSI between any two spatial points, thereby help in developing standards for V2X communications, optimizing antenna placement for vehicles and infrastructure, and better understanding of these V2X systems overall.
Revising the Theory and Practice of Electrical Alignment Procedures for Spherical Near-field Antenna Measurement Facilities
The electrical alignment of the positioner of the Antenna Under Test (AUT) is an important issue to be accounted for before any antenna measurement can take place in a spherical near-field measurement facility. This is because the spherical transmission formula requires the AUT to be scanned on the surface of a sphere. Typically, the tower has been aligned by optical means but, usually, it is necessary to translate it along some axis to place the AUT in the center of the measurement sphere. Furthermore, mounting the AUT can alter the alignment due to its gravitational load. Therefore, alignment of the tower after mounting the AUT is a critical step, which is accomplished with the so-called flip tests . These flip tests, which can detect only the axis intersection and zero-? errors of a roll over azimuth system, have been discussed in the past, for example [1-2], but not as extensively as their importance would require. Moreover, there were no analytical proofs provided for the error formulas given, which forces the interested researcher to derive them again in order to comprehend them and adapt them to his measurement facility. This paper starts with a concise and thorough presentation of how the flip-tests are performed in practice, as well as their theoretical justification. In the second part, the paper presents a novel idea regarding the interdependence of the alignment errors. It has been observed experimentally that two linear coupled equations can model their behavior. Consequently, they can be fully corrected simultaneously with only two flip-tests, without the need of correcting each one in small steps. Simulation tests were performed validating these results. Finally, the paper concludes with addressing a few miscellaneous issues that are inevitably risen by the nature of this procedure, such as the effect of the antenna gain, the positioning of the probe and the distance between the AUT and the probe.
Measurement Traceability in the CISPR 16-1-6 pattern measurements for CISPR 16-1-4 Site Validations
The publication of CISPR 16-1-6  in 2107 marked a significant change in the CISPR documents, for the first time the consideration of how to perform antenna pattern measurements in and determine the associated estimate of the uncertainty of those measurement. This is a look at that technique and presentation of how that helps and relates to measurement traceability.
A Straightforward Dynamic Range Error Analysis
The significant measurement standards in the antenna measurement community all present suggested error analysis strategies and recommendations. However, many of the factors in these analyses are static in nature in that they do not vary with antenna pattern signal level or they deal with specific points in the pattern, such as realized gain, side lobe magnitude error or a derived metric such as on-axis cross polarization. In addition, many of the constituent factors of the error methods are the result of analyses or special purpose data collections that may not be available for periodic measurement. The objective of this paper is to use only a few significant factors to analyze the error bounds in both magnitude and phase for a given antenna pattern, for all levels of the pattern. Most of the standards metrics are errors of amplitude. However, interest is increasing in determining phase errors and, hence, this methodology includes phase error analysis for all factors.
Measurements of Non-Metallic Targets for the Austin RCS Benchmark Suite
A simulation-supported measurement campaign was conducted to collect monostatic radar cross section (RCS) data as part of a larger effort to establish the Austin RCS Benchmark Suite, a publicly available benchmark suite for quantifying the performance of RCS simulations. In order to demonstrate the impact of materials on RCS simulation and measurement, various mixed-material targets were built and measured. The results are reported for three targets: (i) Solid Resin Almond: an almond-shaped low-loss homogeneous target with the characteristic length of ~10-in. (ii) Open Tail-Coated Almond: the surface of the solid resin almond's tail portion was coated with a highly conductive silver, effectively forming a resin-filled open cavity with metallic walls. (iii) Closed Tail-Coated Almond: the resin almond was manufactured in two pieces, the tail piece was coated completely with silver coating (creating a closed metallic surface), and the two pieces were joined. The measured material properties of the resin are reported; the RCS measurement setup, data collection, and post processing are detailed; and the uncertainty in measured data is quantified with the help of simulations.
A Compact Reconfigurable Millimeter-Wave Antenna Measurement System Based Upon an Industrial Robot
Echodyne has recently completed and qualified a new millimeter-wave antenna measurement system for characterization of beam-steering antennas such as our Metamaterial Electronic Steering Arrays (MESAs). Unlike most far-field systems that employ a standard Phi/Theta or Az/El positioner, we use a six-axis industrial robot that can define an arbitrary AUT coordinate system and center of rotation. In different operational modes, the robot is used as an angular AUT positioner (e.g., Az/El) or configured for linear scan areas. This flexible positioning system allows us to characterize the range illumination and quiet zone reflections without modification to the measurement system. With minor modifications, the system could also be used in a planar-near field configuration. Range alignment can be easily performed by redefining the coordinate system of the AUT movement in software. The approximate 5.2-meter range length is within the radiating near-field of many arrays of interest, so we employ spherical near-field (SNF) correction when necessary, using internally-developed code. Specialty tilted absorber was installed in the chamber to improve quiet zone performance, over standard absorber treatment for similar aspect ratio ranges. Narrower ranges often have specular reflections that exceed 60° and benefit from the specialty tilted absorber designed to reduce the angle of incidence. We present an overview of the measurement system and some initial measurement data, along with lessons learned during design and integration. I. MEASUREMENT SYSTEM OVERIVEW A 7.3m x 3.7m x 3.7m footprint was allocated for the new R&D millimeter-wave antenna measurement chamber. After accounting for structural considerations, the final chamber interior dimensions are 7.1m(L) x 3.45m(W) x 3.35m(H) and the final range length (separation between range antenna and quiet zone center) is about 5.2 m. Table 1 lists the high-level goals of the measurement system are listed in. Table 1. Echodyne R&D chamber goals. Parameter Goal Frequency range 12-40 GHz, with provisions up to 80 GHz Polarization Dual-linear switched or simultaneous AUT positioner Azimuth-over-Elevation and linear scanning Quiet zone size 0.4m(L) x 0.4m(W) x 0.4m(H) Side lobe uncertainty +/-1 dB for-20 dB sidelobe Figure 1 shows the dimensions of the rectangular chamber, which is lined with the special absorber design described in Section II. Figure 2 shows an overview of the measurement system. The RF subsystem consists of a 4-port vector network analyzer (VNA), a Gigatronics GT-1050A power amplifier, a directional coupler (placed after the amplifier) to provide the VNA reference signal and a MVG QR18000 dual-polarized closed boundary quad-ridged horn  as the range antenna. This setup provides continuous frequency coverage from 12 to 40 GHz. External frequency converter modules can be used to extend the range further into millimeter wave. Horizontal and vertical polarization are acquired simultaneously by measuring three receiver channels (B, C & R1) and calculating the ratios B/R1 and C/R1 which remove the effects of amplifier drift (such as temperature coefficient). The range antenna is mounted to a rotary stage to allow direct measurement of Ludwig-III polarization if desired (versus polarization synthesis in post-processing). The AUT positioner described in Section III is a six-axis industrial robot that provides both angular azimuth-over-elevation and linear scanning with high-accuracy. Linear scanning allows planar near-field measurements in addition to the quiet zone evaluation shown in Section IV. The 5.2 m range length is within the radiating near-field of many arrays of interest, especially at higher frequencies. For example, even a relatively small (140 mm) AUT would have a 22.5° phase taper across at 40 GHz. We use the spherical near-field measurement correction  described in Section V to obtain true far-field patterns in the Az/El coordinates described by the robot motion. Figure 1. Rectangular chamber dimensions (in inches).
De-embedding Radome Depolarization from Measurements with a Non-Ideal Circularly Polarized Antenna Source
An approximation method is developed to remove the source antenna's cross-polarization discrimination (XPD) contribution from the total measured XPD. This modeling is shown to correlate very well on a flat-panel test with a radome's predicted (ideal-source) XPD. Additionally, a mathematical formulation of the theoretical cross-polarization discrimination (XPD) bounds is presented to validate the proposed method. The measured axial ratio should not exceed these bounds. The measured result is within these bounds and thus this model serves as an additional validation step to both the proposed method and the measured results.
Indoor 3D Spherical Near Field RCS Measurement Facility: A new high resolution method for 3D RCS Imaging
Indoor RCS measurement facilities are usually dedicated to the characterization of only one azimuth cut and one elevation cut of the full spherical RCS target pattern. In order to perform more complete characterizations, a spherical experimental layout has been developed at CEA for indoor Near Field monostatic RCS assessment . This experimental layout is composed of a 4 meters radius motorized rotating arch (horizontal axis) holding the measurement antennas while the target is located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allows full 3D near field monostatic RCS characterization. 3D imaging is a suitable tool to accurately locate and characterize in 3D the main contributors to the RCS. However, this is a non-invertible Fourier synthesis problem because the number of unknowns is larger than the number of data. Conventional methods such as the Polar Format Algorithm (PFA), which consists of data reformatting including zero-padding followed by an inverse fast Fourier transform, provide results of limited quality. We propose a new high resolution method, named SPRITE (for SParse Radar Imaging TEchnique), which considerably increases the quality of the estimated RCS maps. This specific 3D radar imaging method was developed and applied to the fast 3D spherical near field scans. In this paper, this algorithm is tested on measured data from a metallic target, called Mx-14. It is a fully metallic shape of a 2m long missile-like target. This object, composed of several elements is completely versatile, allowing any change in its size, the presence or not of the front and / or rear fins, and the presence or not of mechanical defects, … Results are analyzed and compared in order to study the 3D radar imaging technique performances.
Experimental Validation of Minimum Redundancy Scanning Schemes in PNF Measurements at V band
The planar wide-mesh scanning (PWMS) methodology is based on a non-redundant sampling scheme ,  and is thus without loss of accuracy. It has the potential to enable much faster measurements than standard Planar Near Field (PNF) scanning that is based on denser, regular, equally spaced NF sampling fulfilling Nyquist criteria. In , the non-redundant methodology has been validated numerically by simulated measurements on a highly shaped reflector antenna and with actual measurements on a pencil beam antenna in Ku-band and on a navigation antenna in L-band. In this paper, we present the experimental verification of the PWMS methodology, at V band using dedicated PNF measurements of a Standard Gain Horn antenna MVG SGH4000. The results accuracy of the non-redundant methodology has been investigated against Far-Field patterns, implemented by standard scanning methods, by visual comparison, and by computation of the Equivalent Noise Level (ENL). The achieved under-sampling factor is equal to 12, corresponding to similar time reduction in the stepped measurement system employed for the presented validation.
A Methodology for Instantaneous Polarization Measurements Using a Calibrated Dual-Polarized Probe
Accurately measuring the polarization of an antenna is a topic that has garnered much interest over many years. Methods abound including phase-referenced measurements using two orthogonal polarizations, phase-less measurements using two or three pairs of orthogonal polarizations, spinning linear probe measurements, and the rigorous three-antenna polarization method. In spite of the many publications on the topic, polarization measurements are very challenging and can easily lead to confusion, particularly in accurately determining the sense of polarization. In this paper, we describe a method of accurately and rapidly measuring the polarization of an antenna with the aid of a multi-channel measurement receiver and a dual-polarized probe. The method acquires phase-referenced measurements of two orthogonal polarizations. To enable such measurements, we describe a methodology for calibrating the probe. We also describe a tool for automating the polarization measurement and display of the polarization state. By automating the process, it is hoped that the common challenges and confusions associated with polarization measurements may be largely obviated.
Measurements on extended objects for radar field probes
An extended long object usually gives rise to a bright reflection (a glint) when viewed near its surface normal. To take advantage of this phenomenon and as a new concept, a discrete Fourier transform (DFT) on the RCS measurements, taken within a small angular range of broadside, would yield a spectrum of incident wave distribution along that object; provided that the scattering is uniform per unit length, such as from a long cylinder [1, 2]. In this report, we examine the DFT spectra obtained from three horizontal long objects of different lengths (each of 60, 20, and 8 feet). Aside from the end effects, the DFT spectra looked similar and promising as an alternative to the conventional field probes by translating a sphere across a horizontal path. Keywords: RCS measurements, compact range, field probes, extended long objects 1. The Boeing 9-77 compact range The Boeing 9-77 indoor compact range was constructed in 1988 based on the largest Harris model 1640. Figure 1 is a schematic view of the chamber, which is of the Cassigranian configuration with dual-reflectors. The relative position of the main reflector and the upper turntable (UTT) are as shown. The inside dimensions of the chamber are 216-ft long, by 80-ft high, and 110-ft wide. For convenience, we define a set of Cartesian coordinates (x: pointing out of the paper, y: pointing up, z: pointing down-range), with the origin at the center of the quiet zone (QZ). The QZ was designed as an ellipsoidal volume of length 50-ft along z, height 28-ft along y, and width 40-ft along x. The back wall is located at z = 75 ft, whereas the center of the roll-edged main reflector (tilted at 25 o from vertical) is at z =-110 ft. It is estimated that the design approach controls the energy by focusing 98% of it inside the QZ for target measurements. The residual field spreading out from the main reflector was attenuated by various absorbers arranged in arrays and covering the chamber walls.-, Tel. (425) 392-0175 2. Anechoic chamber In order to provide a quiet environment for RCS measurements, the inside surfaces of an anechoic chamber are typically shielded by various pyramidal and wedged-shaped absorbers, which afford good attenuation at near-normal incidence for frequencies higher than ~2 GHz. At low frequencies and oblique angles , however, Figure 1. A schematic view of the Boeing 9-77 compact range with dimensions as noted. insufficient attenuation of the radar waves by the absorbers may give rise to appreciable backgrounds. Figure 2 shows a panorama view inside the compact range, as viewed from the lower rear toward the main reflector and the UTT. With the exception of the UTT, all other absorbers are non-moving or stationary. A ring of lights on the floor shows the rim around the lower turntable (LTT), prior to the installation of absorbers. In order to minimize the target-wall interactions, the surfaces facing the QZ from the ceiling, floor, and two sidewalls are covered with the Rantec EHP-26 type of special pyramidal absorbers.
Use of OTA System Performance Metrics in the Design & Optimization of CATRs for 5G Testing
Delivering on the promise of 5G measurements requires the adoption of new RF system technologies that encompass both the mobile user equipment and the active base station. Keeping pace with the impact of new wireless system test parameters such as: Data throughput, Error Vector Magnitude, Symbol Error Rate, and technologies such as mm-wave Massive MIMO, OFDM, and QAM presents significant challenges to antenna test community. For the most part, the market has attempted to react by adapting traditional test equipment to the wireless market however 5G testing presents an ever-greater challenge and demands the incorporation of simulation effects when designing and optimising an antenna test system, especially as these systems have increased in complexity with the adoption of the indirect far-field method and specifically the compact antenna test range (CATR). This paper discusses how 5G communication system parameters affect the design of the CATR and how newly developed simulation capabilities have been incorporated to optimize the CATR design for 5G test applications.
A Review of the Changes and Additions to the Antenna Measurement Standard IEEE Std 149
The IEEE Standard 149, Standard Test Procedures for Antennas, has not been revised since 1979. Over the years the Standard was reaffirmed, that is, its validity was re-established by the IEEE APS Standards Committee, without any changes. Recently however, the IEEE Standards Association stopped the practice of reaffirming standards. This change in policy by the IEEE has been the "medicine" that this Standard needed. A working group was organized and a project authorization request (PAR) was approved by IEEE for the document to be updated. In this paper, the expected changes to the document are described and commented. The main change is to convert the Standard to a recommended practice document. Additionally, some new techniques to measure antennas, such as the use of reverberation chambers for efficiency measurements and more information on compact ranges, is discussed. Other topics inserted are more guidance on indoor ranges and an updated section on instrumentation. Most importantly, a discussion on uncertainty is included. The result will be a very useful document for those designing and evaluating antenna test facilities, and those performing the antenna measurements.
Proposed Changes and Updates on IEEE Std 1128 - Recommended Practice on Absorber Evaluation
The last published version of the IEEE Std 1128 is the 1998 edition. It is titled "Recommended Practice for RF Absorber Evaluation in the Range of 30 MHz to 5 GHz". Over the years, the document has been used widely for absorber evaluations in electromagnetic compatibility (EMC) applications as well as in antenna and microwave measurement applications. Besides the obvious frequency range which needs to be expanded to satisfy today's applications, several areas are in need of an update. The proposed document will change the upper frequency limit to 40 GHz (with provisions in the document to potentially extend above 40 GHz based on test methods). Measurement uncertainties were not discussed in the IEEE Std. 1128-1998. In the new edition, measurement instrumentation and test methods are expected to be updated with guidance on estimating measurement uncertainties. In the proposed document, a section on absorber evaluations for high power applications is planned, and fire properties and test methods will be included.
Accurate Calibration of Truncated Spherical Near Field Systems with Different Ground Floors using the Substitution Technique
The calibration of the antenna measurements system is a fundamental step which directly influences the accuracy of any power-related quantity of the device under test. In some types of systems, the calibration can be more challenging than in others, and the selection of a proper calibration method is critical. In this paper, the calibration of the truncated spherical near-field ranges typically used for automotive tests is investigated, considering both absorbing and conductive floors. The analyses are carried out in a 12:1 scaled multi-probe system, allowing access to the "true", full-sphere calibration which is used as reference. It will be demonstrated that the substitution (or transfer) method is an excellent calibration technique for these types of systems, if applied considering the efficiency of the reference antenna.
Non-contact Characterization of Antenna Impedance, Gain and Pattern through Open-Fixture Network Calibration
We present a novel, non-contact characterization technique for simultaneous characterization of conventional antenna parameters, including the antenna port input impedance, antenna gain and its radiation pattern, without requiring a network analyzer connection to the antenna port. The test antenna and the network analyzer are considered as a 2-port open-air fixture whose network representation corresponds to the desired antenna parameters. The unknown network parameters of the 2-port open-air fixture are determined via a novel calibration process using 4 offset-short termination standards. The error parameters determined by the calibration are then related to the test antenna port impedance and its gain as a function of frequency. Furthermore, the radiation pattern of the test antenna can also be characterized using measured reflection coefficient at the network analyzer port for two offset-short terminations of the test antenna port, while rotating the test antenna over the desired angular range. This novel technique is particularly attractive for installed-antenna applications where an active connection to the test antenna port is either difficult or undesirable, such as on-chip antennas and implanted antennas, to name a few. To demonstrate the efficacy our new method, we present the measured impedance, gain and radiation pattern of a diagonal-horn antenna operating over 360-450 GHz, and a lens-integrated planar butterfly antenna for the 220-325GHz band.
Generalized Test-Zone Field Compensation
Antenna measurement errors occur due to reflections and diffractions within the measuring chamber. In order to extract and correct the undesired signals, a technique based on test-zone field compensation and spherical wave expansion is applied to Compact Antenna Test Range (CATR) and Spherical Near-Field (SNF) measurements of a base transceiver station antenna. The required spherical test-zone field is acquired by simulating the corresponding measurement environment with the multi-level fast multipole method. Due to the numerical complexity of the problem, only the parts of the chamber with a significant influence on the measurement results are modeled. Comparing the determined directivities after applying the correction method, an exact overlap is achieved between the SNF and CATR solution.
Experimental validation of Reference Chip Antennas for 5G Measurement Facilities at mm-Wave
In this paper, the experimental validation of a micro-probe fed reference antenna targeting the upcoming 5G applications (24.25-29.5GHz band) is presented. The main purpose of these reference antennas is to serve as "gold standards" and to perform gain calibration of 5G test facilities through the substitution method. The outline of these antennas is based on a square array of four printed patches enclosed in a circular cavity. The RF input interface is a stripline-to-coplanar waveguide transition and allows for feeding the device with a micro-probe. Performance obtained by high-fidelity modeling is reported in the paper and correlated to experimental data. Interaction and unwanted coupling with the test equipment are discussed. The use of echo-reduction techniques and spatial filtering is investigated to mitigate these effects.
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