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A Unique Spherical Near-Field Test System for Commercial Aircraft Radar Radome Testing
Kefeng Liu, Anbang Liu, Denis Lewis, October 2023

A novel test system has been developed using the Spherical Near-Field (SNF) test method to test commercial aircraft radar radomes fully complying to the RTCA-DO-213 Change 1A [1] test requirements. In contrast to either a compact range or a far-field outdoor range to test directly for far-field patterns, this test range employs a fixed scan area SNF test method [2] and transforms the near-field patterns to the required far-field patterns. This test system has the advantage of a more compact test site size than the other two types of test ranges; yet maintains a long enough test distance to minimize the radiated near-field coupling between the probes and the Antenna Under Test (AUT) to a negligible level. The test system also features a multi-axis AUT positioner that supports relative angular positions between the radome and the radar panel antenna to simulate both AZ/EL and EL/AZ gimbal motions as required by RTCA-DO-213A specifications. Additionally, a multi-probe SNF scan antenna system is employed to expediate SNF data acquisition. This compact, high precision SNF antenna test system also demonstrates the potential to eliminate the need for λ/4 shift in the test distance as required by RTCA-DO-213 Change 1A, resulting in a potential 50%-time savings in transmission efficiency testing using the near-field test method when the test distance is much greater than the required 10λ. Furthermore, it also demonstrates the potential to reduce the number of reference antenna pattern tests for transmission efficiency from 231 to 1, since the panel antenna is stationary during each of the 231 test configurations and will be of the same AUT patterns. Test data supporting the accuracy and efficiency of this test system is also documented.

A Squat Cylinder-Dihedral Dual Calibration Device for Compact Ranges at UHF
Hirsch Chizever, Laura Suzuki, October 2023

The use of squat cylinders as both primary and secondary calibration targets is commonplace within the radar cross section (RCS) measurement community. Secondary calibrations have become a best practice activity for ranges seeking or maintaining certification. The calibration process, often referred to by the measurement community as a “Dual-Cal,” uses two squat cylinders of similar but unequal dimensions that provide range operators with a broadband calibration vector and a measurement uncertainty metric important to range certification. Despite their popularity, the need to ensure resonance scattering occurs below the desired measurement band results in physically large cylinders at UHF. In addition, the need to access the test zone for separate cylinder measurements may add substantial time to the calibration process and require specialized equipment, especially for large ranges. In response to these issues, a 22.5-degree right dihedral has been inserted into a squat cylinder form factor, creating a primary and secondary calibration target within one body, each separated in azimuth by 180 degrees. This two-target calibration device removes the need to access the target zone twice and mitigates errors associated with separate mounting schemes. The cylinder aspect, now truncated by the imposition of a dihedral, has 50% extended lower frequency coverage at UHF due to oblique edge scattering at vertical polarization. At horizontal polarization, the dihedral interruption of the cylinder creeping wave reduces its contribution for ka<4. The dihedral aspect provides a full polarimetric calibration, resulting in co-equal frequency responses for each polarization in the high frequency limit. The design parameters of the squat cylinder-dihedral device, its computed full-wave frequency response, and relevant scattering features are discussed.

New Designs for a Feed Fence to reduce the direct coupling to the Quiet Zone on Compact Ranges
Mark Ingerson, Vince Rodriguez, Daniel Janse van Rensburg, Anil Tellakula, October 2023

Absorber fences have been used on compact ranges since their first implementations. The purpose of this fence is to hide the feed positioner and reduce the direct coupling between the feed and the device under test (DUT). A known problem caused by such a fence is that it diffracts the plane wave generated by the reflector, creating an interfering ripple on the illumination of the DUT in the quiet zone. Traditionally, fences have serrated edges to direct this diffracted signal away from the quiet zone. However, this redirection is not always achievable or even repeatable from one facility to the next. Often low frequency requirements drive absorber physical size, leading to very large absorbing surfaces that cannot be optimized to reduce this interfering signal. In this paper, the fence design presented in a recent publication [1] is further optimized by modifying its shape and absorbing material parameters. The performance of this new design is compared with traditional fences.

Accurate Evaluation of Antenna Measurement Range Performance with the SWE Transmission Formula
Francesco Saccardi, Andrea Giacomini, Lars Foged, October 2023

The spherical wave expansion-based transmission formula allows to accurately evaluate the coupling (or S21 parameter) between a transmitting and a receiving antenna. Its use as tool for probe corrected spherical near-field to far-field transformation is well accepted and documented. On the other hand, its direct use in the evaluation of antenna measurement performance has been exploited only in recent years. In this paper we will show how measurement performances predicted with the transmission formula compare with actual measurements. Taking as examples relatively complex antenna measurement systems like spherical near-field, plane wave generators and CATR, we will focus on the prediction of the accuracy of the measured radiation patterns, also including the approximation of reflections from the test environments, and on the evaluation of link budgets.

Compact RCS Test Range Feed Carousel and Baffle House Design
Gil Yemini, Stefano Sensani, Andrea Giacomini, Lars Foged, Marcel Boumans, Matan Kahanov, Maria Baskin, Ilan Kaplon, October 2023

A new compact range for RCS measurements has been installed and qualified by Orbit/FR Engineering Ltd. MVG. It has a Quiet Zone of 3m diameter, 3m length and operates from 0.7 to 50 GHz, with a feed carousel that allows for fully automated feed change. The RF design is not intended for antenna measurements in its current configuration, but mainly dedicated to RCS. The operational frequency band is split into three sub-bands: each of the lower two bands have a monostatic operated dual polarized feed, while the higher band has a quasimonostatic operated feed configuration with two dual polarized feeds. Pulsed Tx/Rx modules are directly integrated into the feed assembly. Also, the RF band switching equipment, as well as the network analyzer, are integrated in the feed carousel, so that there are no flexing cables or any other relative movement of RF components when the relevant feed is moved into the focus. Together with tight temperature control, this leads to the best possible RF stability. Since all measurements are time gated, there is no need for an absorber baffle wall to prevent feed direct leakage into the quiet zone. Thus, all feeds are mounted on a clean absorber disk without any absorber blockage and unwanted primary pattern distortion down to a conical angle of 90deg. This allows to obtain an exceptionally good QZ performance even at the lowest frequencies, with an outstanding comparison with the predictions based on Physical Optics. The paper will describe the range design fundamentals, the feed carousel concept and the relevant RF instrumentation. The Quiet Zone performance evaluated by field probing with a Shorted Antenna located in the Quiet Zone will be extensively presented, demonstrating full compliance with the specifications.

Compact RCS Test Range Field Probing using a Shorted Antenna as Target
Gil Yemini, Stefano Sensani, Andrea Giacomini, Lars Foged, Marcel Boumans, Matan Kahanov, Maria Baskin, Ilan Kaplon, October 2023

A new compact range for RCS measurements has been qualified. It has a quiet zone of 3m diameter, 3m length and operates from 0.7 to 50 GHz. The range is oriented for RCS measurements, whereas antenna measurements are not foreseen. All RF equipment is integrated close to the feeds with highly integrated pulsed Tx/Rx-modules. Therefore, classical field probing by moving a probe antenna along a linear slide would require significant modification of the RF system. If one measures the RCS of a target on the linear slide, it is difficult to distinguish the target down range reflection from the reflection of the linear slide structure. A long stand-off between target and slide is not practical for mechanical reasons in regard to accuracy requirements at 50 GHz. More important, simply measuring a reflective plate will not give any cross-polarization information. A more advanced target is created by using an antenna with a short circuit after an RF cable to locate the reflection of the short well behind the scanner in down range. In addition, the antenna receives only nominal quiet zone co-polarization, consequently, only reflects co-polarization from the short, and the feed receives the compact range induced cross-polarization at the feed (oneway). The method has shown to be extremely effective. More important, it uses the RF instrumentation and RCS measurement methods as designed for regular operation without any modification, thus is the most realistic system level quality representation of the quiet zone, can be repeated at any time without elaborate range reconfiguration requirements and can serve as part of the commissioned RF system performance qualification. The paper will present the quiet zone field probe test setup, a calculation of antenna and RF cable requirements, an analysis of the down range profile of scanner and reflective antenna and field probing results.

Accurate Antenna Characterisation at UHF/VHF Frequencies with Plane Wave Generator Systems
Lars Foged, Francesco Saccardi, Vincenzo Schirosi, Andrea Giacomini, Francesco Scattone, Lucia Scialacqua, Arianna Diamanti, Enrico Tartaglino, Nicolas Gross, Shoaib Anwar, Evgueni Kaverine, Per Iversen, Edward Szpindor, October 2023

This paper aims to compare the capabilities and advantages of Plane Wave Generators (PWG) and Compact Antenna Test Ranges (CATR) of similar physical size, operating in the VHF/UHF frequency range. The primary focus of this study is on the benefits of utilizing the PWG at such low frequencies for antenna and device characterization. We demonstrate that the PWG offers a superior approximation to the far-field (FF) plane wave condition in the quiet zone (QZ) compared to similar sized CATR systems. The better performance of the PWG at these frequencies is expected, as this is an unusual frequency range for an optical system such as CATR. Due to the efficient focusing properties of the array, the PWG exhibits significantly reduced side wall illumination and thus resulting reflections within the anechoic chamber. This translates into a substantial improvement in overall measurement uncertainty. The CATR system requires specific edge treatment, such as serrations or rolled edges, which increase the overall system's size and associated cost while reducing the effective area of the reflector. Our findings suggest that at low frequencies such as VHF/UHF, a PWG-based solution can be designed to comparable performance to the CATR system while maintaining a considerably smaller size and lower cost, making it an attractive alternative for low frequency antenna testing at in anechoic environments.

Horn Antenna Manufacturing Using Additive Manufacturing Techniques
Jeffrey Fordham, Jon Swarner, Eric Kim, Griffin Fox, Corey Agan, October 2023

Additive manufacturing methods, also known as 3D printing, have proven to offer many advantages in manufacturing a wide range of products. These methods have advantages of rapid prototyping, rapid production, and the ability to produce mechanical parts that cannot be realized with traditional machining or casting methods. Various methods have been developed which use a wide variety of raw materials and methods. For example, the Selective Laser Sintering (SLS) method has been used in 3D printing of antennas [1], where metal conductivity is required along with accurate mechanical tolerancing. Other methods using plastic such as stereolithography (SLA) where a liquid photopolymer resin is cured using an ultraviolet laser and Fused Deposit Modeling (FDM) material extrusion where a plastic wire is melted and deposited layer by layer to construct the part are being used to produce RF components and antennas. In the case of plastics, a conductive layer must be deposited onto the plastic to ensure conductivity. Recent work toward the development of horn antennas produced using SLS, SLA and extrusion methods has been accomplished. The methods have been shown to produce horn antennas capable of meeting a variety of applications in the test and measurement industry where accuracy and repeatability are key metrics. A comparison of methods is presented along with advantages and disadvantages. Performance data will be presented for some horns showing the capabilities of the various methods.

Measurement Uncertainties in Outdoor Far-field Antenna Ranges
Edwin Barry, Pieter Betjes, Eric Kim, October 2023

Consolidated methodologies have long been established to assess measurement uncertainties in near-field antenna measurements. More recently, similar detailed approaches have been developed for compact ranges and adopted as standard practice. However, currently there is no analogous methodology for outdoor far field measurement facilities. This paper presents a framework for assessing the measurement uncertainties on an outdoor far-field elevated range. Various sources of uncertainty in an outdoor far-field range are identified, using the industry standard 18 term analysis for nearfield range assessment as a baseline. An example analysis based on an actual outdoor far-field range is presented. The uncertainty terms are quantified by analysis, observation, or measurement, and finally combined by the root sum squared method to arrive at the gain uncertainty and the -30 dB sidelobe level uncertainty.

New Methods for Extraction of VHF Electrical Properties of Conductive Coatings
Ren Geryak, John Schultz, October 2023

This paper describes two reflection methods to measure highly conductive coatings at VHF frequencies: 1) a resonant method based on eddy-current sensing at HF and VHF frequencies, and 2) a wideband method at VHF and UHF frequencies, based on a shorted transmission line combined with and computational electromagnetic (CEM) simulations to invert surface impedance. In both cases, the methods are able to determine surface impedances with sensitivities of a small fraction of an ohm. Both methods have strengths and weaknesses with respect to ease of calibration, sensitivity, frequency range, and use on non-flat surfaces. This paper describes both approaches and presents measurements on a variety of conducting materials and coatings. The resulting properties are also compared with DC conductivity measurements collected with a four-point probe system. The predicted accuracy for both methods is presented based on simulated data and empirical measurements.

Tunable Cellular Desensitization using SD Card Data Transfer
Michael Foegelle, October 2022

For some time now the CTIA W-IoT OTA Reverberation Chamber Ad-Hoc Group has been looking for an OTA test artifact that exhibited repeatable narrow band cellular desensitization so that it could be used to perform round-robin testing between labs and investigate the impact of different test methodologies (e.g. reverberation chamber vs. spherical antenna pattern measurement in an anechoic chamber) on intermediate channel desense testing. Since device manufacturers aren't eager to provide devices with known problems, some alternative was required. Attempts were made to modify a device by removing shielding cans, only to completely degrade device performance across the entire spectrum. Using an external signal generator feeding a coupler at the DUT was also considered, but cable effects and equipment variations would have impacted repeatability in the variety of anticipated test environments. Creating a custom device with an embedded interference source met with cost and other practical limitations that stalled progress along that avenue. A member of the working group related anecdotal evidence suggesting that SD card communication within the phone was known to be a problematic noise source that could cause cellular desensitization. Initial investigation centered on the use of an off-the-shelf SD card testing app to try to generate uniform traffic, but none of the evaluated tools had an option for continuous testing. Focus then turned to developing a custom app for the purpose, but later changes to the Android operating system have deprecated the use of external SD cards, removing standardized support and making the development of a custom application impractical. Another possible solution for long duration interference would be to just play a video from the SD card, but the variability of a typical compressed MPEG video, both in content and compression level, would likely cause surges of data transfer with pauses in between. What was needed was a solution to cause continuous data transfer with a constant signature (i.e. sending the same data constantly) to ensure stability and repeatability. Thus investigation turned to creating a customized video file in an uncompressed format to address these limitations. This paper will show the results of this effort.

Optimization of In-Vehicle Connectivity through Simulation-Augmented Antenna Measurements
Benoit Derat, Mert Celik, Winfried Simon, David Schaefer, Adrian Fleidl, Konstantin Schorp, October 2022

As radiocommunications and internet-based services have become ubiquitous, customer expectations for infotainment capabilities and reliability in vehicles have largely increased. As such, the optimization of the distribution and orientation of antennas within the car is required to deliver the adequate connectivity performance. Yet, making direct measurements of electromagnetic field distributions radiated by structure-integrated radiofrequency transceivers is extremely tedious, if not practically and economically impossible. Recent papers introduced the approach of simulation-augmented measurements, appearing as a relevant solution to that problem. This method relies on a three-step approach: (i) measure the phasor electric field radiated by the standalone or part-integrated antenna module around the test sample; (ii) use an algorithm to calculate equivalent electric and magnetic currents over a surface closely encompassing the device under test (DUT); (iii) inject these currents as a Huygens source into a full-wave solver, where the complete scattering and absorbing environment is then taken into account. This paper presents the concrete application of this approach to the evaluation of the electric field inside a vehicle, based on separate measurements of WiFi and Bluetooth antennas. These measurements are performed using a spherical near-field system, with either the standalone antennas as DUT or the antennas embedded into the physical middle console of a car. The equivalent sources generated from experimental data are then imported into the virtual car model, and interior electromagnetic fields are computed using the Finite-Difference Time-Domain technique. The assessment is realized for various conditions without and with driver and passengers. The results are analyzed and limitations, as well as uncertainties of the technique are discussed.

Acceleration of Over-The-Air Measurements Under Extreme Temperature Conditions Through Optimization of Air Flow and Thermal Efficiency
Benoit Derat, Ralf Meissner, Anes Belkacem, Guenter Pfeifer, Constantin Sinn, Markus Herbrig, Jose Fortes, October 2022

5G communications have supported the deployment of millimeter-wave beam-steering technologies at an unprecedented commercial scale. Mobile phones operating in frequency ranges above 20 GHz integrate antenna arrays and radiofrequency front-ends which control magnitudes and phases of signals to enable adaptive beam-steering. As per the 3GPP Test Specifications, a large number of tests covering the various operational modes of such devices are required in order to establish that the performance is adequate for guaranteeing the integrity of the mobile network. The defined measurement methodology relies on Over-The-Air (OTA) evaluations in Compact Antenna Test Ranges (CATR). As mobile wireless user equipment are practically utilized in diverse environmental conditions, a part of the test plan imposes spherical OTA measurements at extreme temperature conditions ranging from -10 to +55° C. Such temperatures indeed influence the active electronics in the device under test (DUT) and hence the beam-forming performance. This paper presents an innovative realization of a CATR with embedded thermal chamber supporting the above-described test capabilities. Inventive steps are introduced to solve the complex engineering problem of allowing fast temperature ramps to go through the complete range in a few minutes, while allowing two-axis rotations of the DUT, and all of this with preventing damages from the anechoic chamber and positioner and limiting the radiofrequency impact of the thermal testing chain. Thermal and air flow simulation and measurement results are presented, establishing how the design allows sustaining high pressure with low air leakage. Measurements of the quality of quiet zone with and without thermal enclosure demonstrate the limited RF impact of the introduced materials encapsulating the DUT. The derived solution is applied to measurements of a commercial 5G mobile phone, illustrating the influence of the environment on the DUT operation and corroborating the need for such test scenarii.

EMF simulation of base station antennas in real sites using Spherical Wave Expansion and diffracted fields
Celia Fontá Romero, Alicia Auñón Marugán, Fernando Rodríguez Varela, Pablo Bielza López-Manterola, José Luis Alcolea Coronel, José Ignacio Alonso Montes, Manuel Sierra Castañer, October 2022

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.

Using a VNA Based Spherical Near Field Antenna Measurement System for Active Antenna System Performance Verifications
Chang-Lun Liao,, You-Hua Lin, Ike Lin, Bo-Cheng You, Chang-Fa Yang, De-Xian Song, Wen-Jiao Liao, Yuan-Chang Hou, Tswen-Jiann Huang, October 2022

Nowadays, 5G new radio and commercial networks have been widely developed and deployed by many communication service providers around the world. State-of-the-art techniques such as massive multiple input multiple output systems, 3D beamforming technologies, etc. are utilized to enhance spectral efficiencies and system capacities within cellular coverage areas. Additionally, 5G base stations with active antenna systems (AAS) are comprised of the passive antenna array, transceiver frontend and base band units, all integrated into one module, so that the traditional antenna RF ports are replaced with ethernet-based interfaces. Consequently, different from conventional 4G antenna system verification processes, to ensure the optimal cellular signal coverages of the 5G AAS base stations, new measurement methods to verify the radiation properties at RF carrier frequencies of the AAS need to be employed. The radiation pattern test method of the AAS by using a vector network analyzer (VNA) based spherical near field antenna measurement system through over-the-air (OTA) to obtain the magnitude and phase distributions of the electromagnetic fields from the antenna under test (AUT) with single-tone transmitting will be presented in this paper. In order to verify the above mentioned concepts, a signal generator is used to provide the single-tone source into a commercial passive base station antenna. Also, two received channel connections to the VNA are included, where a reference antenna placed adjacent to the back of the AUT for phase recovery is added together with the existing probe of the spherical near field antenna measurement system for reconstructing the near-field amplitude and phase of the fields during scanning. Thus, the near-field to far-field transformations and back projections can be performed for active antenna performance verifications. Radiation patterns obtained by the above OTA near field measurement method demonstrate good agreements with those from conventional near field tests at 3.5 GHz for 5G FR1 AAS performance verifications.

Cylindrical Near-Field Measurement and Far-Field Characterization of 300-GHz Band Antenna Based on an Electrooptic Measurement Technique
Yusuke Tanaka, Shintaro Hisatake, October 2022

We demonstrate cylindrical near-field measurement and far-field characterization of 300-GHz band antennas using photonics-based technologies. The measurement system is based on a self-heterodyne technique and non-polarimetric frequency down-conversion technique in which an electrooptic (EO) sensor was used. An optical beat signal generated using two 1550 nm laser diodes with the difference frequency of 300 GHz was EO converted by a uni-traveling-carrier photodiode (UTC-PD) to generate 300 GHz RF signal. The material of the EO crystal was a DAST (4-N,N-dimethylamino-4-N-methyl stilbazolium tosylate) and the dimension was approximately 0.5 mm x 0.5 mm x 1 mm. The EO probe was composed entirely of dielectric material, thus the scattering by the probe was minimized. In addition, the use of optical fiber significantly reduces scattering compared to conventional probe antennas that use metal cables or waveguides. As an optical local oscillator signal (LO signal), a coherently frequency-shifted optical beat signal generated based on the self-heterodyne technique was used. By tuning the frequency of one laser diode, the frequency of the RF signal can be swept. The system bandwidth is limited by the bandwidth of the UTC-PD, which covers WR-3.4 band (220-330 GHz). The RF signal up-converted to the optical domain in the EO crystal was coherently detected by a low-speed photodiode to generate intermediate (IF) frequency signal. The amplitude and phase of the IF signal, which are copies of those of the RF signal, were detected with a lock-in amplifier. The antenna under test (AUT) was a rectangular-type horn antenna (WR-3.4) with an antenna gain of approximately 25 dBi. The AUT was rotated by ±45° horizontally and the EO probe mounted on a 4-axis robotic arm was linearly moved vertically by ±15 mm to measure the cylindrical near-field distribution. The far-field distribution was estimated by transforming the measured cylindrical near-field distribution without probe correction. The simulation results and measured results were agreed very well. In E-plane, the first to third sidelobe levels agreed within 1 dB. The 3dB beamwidths of the measured result were 10.3° and 9.5°, whereas those of the simulated results were 9.5° and 9.7°, in the E- and H- plane, respectively.

Investigation of Inhomogeneity of Material Characteristics on the Hybrid-Absorber Performance
Amin Enayati, October 2022

With the growing applications of wireless systems in different aspects of everyday life, from the consumer-electronic devices to internet-of-thing applications to wireless health-monitoring systems, there is an expanding need for reliable measurement of the radiating performance of these devices. The electromagnetic compatibility (EMC) tests, including immunity and interference tests, are normally done in shielded rooms the walls of which are covered by the so-called hybrid absorbers. These absorbers are made of a magnetic lossy layer giving absorption at low frequencies and a dielectric lossy geometrical absorber which is mainly responsible for the electromagnetic absorption at higher frequency range. The heart of hybrid-absorber design, which can be reduced to a wide-band matching problem, is to match the dielectric lossy part to the magnetic lossy layer. The magnetic layer which is mostly made up of a ferrite material, is a relatively thin layer, i. e. less than 1 cm thick, which is supposedly homogeneous. The dielectric geometrical absorber part has a relatively large thickness, e.g. 30 inches, and incorporates geometries like a pyramid to make a tapering against the wave which is going to be absorbed by the absorber. Because of the relatively large thickness of the dielectric lossy part and the production-process techniques used to make these parts, there are inhomogeneities in this part. In the current paper, the impact of the inhomogeneity of the dielectric part on the matching performance of the hybrid absorber is investigated in details. In the 1st stage, a 30-ich absorber is chosen and sliced in 15 different layers the permittivity is of each measured separately. Using these permittivity values, a complex model is made and simulated to get an expected reflectivity value on the ferrite layer. In the 3rd step, the absorbers of the same production batch are chosen to be measure in real-scale measurement setup and the reflectivity values are measured. Finally, the measurement and simulation results are compared and the impact of inhomogeneity of the dielectric absorber on the hybrid-absorber performance in concluded.

Numerical and Experimental Validation of Near-Field Power Density Reconstruction from Radiative Field Measurements
Benoit Derat, Martin Wittmann, Mert Celik, Walid El Hajj, Davide Colombi, October 2022

For millimeter-wave wireless devices used in the close proximity to the human head or body, the compliance evaluation to regulatory exposure limits is determined from near-field free-space power density measurements. For mobile phones and other portable equipment, the standard assessment technique involves the characterization of the power density on planes, as close as 2 mm from each facet of the device under test (DUT), as well as on anthropomorphic surfaces. These measurements are typically realized by means of a pseudo-vector diode-detected probe, acquiring the electric field magnitude and polarization ellipse at multiple locations over the scanning area. Phaseless techniques have been employed to deduce the required phase and magnetic field information for the calculation the Poynting vector. Although accurate, this technique presents some limitations: prohibitive test times; the inability to distinguish between various frequency contributions of the electric field due to the detection process; or the necessity to implement specific test modes in the DUT to fix the radiated beam in a given state. A recent paper proposed an alternative method which overcomes these listed limitations. The approach relies on the use of spherical antenna / over-the-air (OTA) phasor electric field acquisitions in an anechoic chamber environment, performed in the radiative field region and combined with near-field processing through equivalent currents reconstruction. This paper proposes an extensive validation of this method based on simulations and measurements of reference antennas, as defined in the IEC 63195. The reference measurements are realized with a standard-compliant 6-axis robot assessment system. The uncertainty contribution coming from probing at distances where reactive field components cannot be captured is investigated, demonstrating a negligible influence on reconstructed field distributions down to a third of the wavelength from the reference antenna, for which a theoretical interpretation is provided. It is also shown that characterizing the detailed changes in the reactive field is not necessary to obtain an accurate peak spatial-average power density value, which is the relevant metric for compliance assessment. A systematic analysis of the error affecting this specific quantity is also provided.

Numerical considerations to improve the Reduced-Order Model Approach for Antenna Measurements
Benjamin Fuchs, Laurent Le Coq, Michael Mattes, Nicolas Mézières, Samuel Corre, October 2022

The characterization of antennas is a time-consuming task. Its acceleration leads often to large and sensitive numerical problems. Therefore, special care must be taken of the choice of the parameters, the optimization, and the stability of the employed resolution methods. Based on Huygens’ principle, the radiation operator can be defined from an equivalent surface enclosing the Antenna Under Test (AUT). The discretization of this operator leads to the so-called radiation matrix. An expansion basis of the fields radiated from the equivalent to the measurement surface is constructed by the Singular Value Decomposition (SVD) of that matrix. The Reduced-Order Model (ROM) is the compressed representation of this basis obtained by truncating the SVD. The truncation order, T, is computed by inspection of the singular value distribution and is strongly linked to the number of degrees of freedom of the radiated fields. Several practical and technical aspects are studied in this article to provide a systematic, efficient and reliable procedure for the characterization of the radiated fields using the ROM. Analytical criteria are used to define the dimensions of the radiation matrix enabling a stable determination of the compressed basis. The truncation order, T, is the key-point of this method as it determines the size of this basis. Therefore, its variation is studied with respect to the discretization step and the geometry of both equivalent and measurement surface. Finally, the Randomized SVD (RSVD) is used in order to significantly reduce the computation time with negligible impact on the accuracy. To illustrate our procedure, it is applied to various scenarios and experimental results of spherical measurements. Estimations of the time savings by using the RSVD are also provided.

Ultra-thin EBG backed flexible antenna for 24 GHz ISM band WBAN
Mubasher Ali, Irfan Ullah, John Batchelor, Nathan Gomes, October 2022

“A novel, ultra-thin, electromagnetic bandgap (EBG) backed antenna is presented for 24 GHz ISM band wearable applications. The via-less EBG unit cell shows both Artificial Magnetic Conductor (AMC) and EBG Characteristics. With dimensions of 0.254λ0× 0.254λ0, it is easy to fabricate at a millimeter-scale. The antenna has bow-tie slots, designed with an overall dimension of 0.91λ0 × 0.84λ0 × 0.01λ0, backed by a 5 × 5 element 0.01λ0 thick EBG/AMC structure; it is manufactured on a flexible Rogers 5880 substrate (thickness = 0.127 mm, = 2.2, tanδ = 0.0009). The proposed antenna is the thinnest (0.02λ0) EBG-backed antenna when compared to available K-band EBG-backed antennas. The performance of the EBG-backed antenna in terms of reflection coefficient and free-space radiation patterns is investigated in scenarios with and without structural bending. It is shown that the integration of the EBG enhances the antenna’s front-lobe gain by 2.63 dBi, decreases back-lobe radiation by 12.2 dB, and decreases 93% the specific absorption rate (SAR (1 g)) from > 28 W/kg to <1.93 W/kg, significantly reducing potential harm to the human body. Furthermore, the EBG-backed antenna was analyzed under a tough on-body and structural deformation measurement setup and the results show the performance of the EBG-backed antenna is highly insensitive to body proximity, and that its performance is preserved when bent along either axis. Therefore, Proposed EBG backed antenna structure demonstrates suitability for K band conformally mounted WBAN applications.”
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