Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
The characterization of antenna radiation pattern is a costly but a mandatory step for the development of any radiating system. Nowadays, these assessments commonly call for the estimation of the whole 3D radiated far field. Such evaluation is a time consuming task and many research works aim to minimize its impact on the whole prototyping process. Of course, the expected accuracy on the results has to be preserved in the meantime. To this end, two main approaches can be cited: reducing the field acquisition time or decreasing the cost of the measurement system itself. The first point can be achieved by more efficient sampling strategies (number of field samples as well as their spatial distribution) and the second one by magnitude-only, or phaseless, measurements. Unfortunately, phase retrieval problems are notoriously hard to solve and these numerical difficulties may be mitigated by considering large field samples, which goes against the reduction of the field acquisition time. We propose a phaseless measurement procedure in far field that amounts to solve a convex optimization problem to overcome the numerical difficulties arising in characterization of antenna radiation patterns from magnitude-only samples. More specifically, a regularization is applied to the spherical wave expansion of the radiation pattern to promote physical solutions. The proposed approach enables an accurate characterization of the far-field magnitude pattern from a small number of samples with respect to usual phaseless procedures. The proposed approach is confirmed by several experimental validations done at IETR that will be shown at the conference.
Digital array technology has advanced over the past few years to where it is now possible to build a large, wideband, multi-element digital array that can produce multiple steerable beams from the same aperture. These types of systems often have the analog-to-digital and digital-to-analog converters (ADC/DAC) and radio-frequency (RF) front end mated directly to the antenna, requiring a new measurement technique as the antenna under test (AUT) cannot be connected to traditional RF measurement equipment. Several years ago the Air Force Research Laboratory (AFRL) Sensors Directorate developed a custom 32 element uniform linear array using commercial off-the-shelf (COTS) low-noise amplifiers (LNAs) and a multi-channel digital receiver. Custom software was developed to perform automated element and digital beam pattern measurements using the compact range position controller. Hand tuned calibration parameters were calculated to form the digital beams. This work demonstrated feasibility of digital array measurement within a compact range environment. Recently AFRL has developed a highly integrated digital array with 1024 elements, LNAs, high-power amplifiers (HPAs), attenuators, phase shifters, transmit/receive switches, polarization switches, and eight multi-channel digital receiver/exciters. Measurements were required to not only test the functionality of the digital array, but also to build a calibration table for each element across the full frequency range of the array. The hand-tuned calibration method developed for the 32 element array was automated in order to build all of the necessary calibration tables for the 1024 element array. Calibrated beam patterns were also collected to analyze beam shape and pointing angle metrics. Following compact range measurement, the 1024 element array was relocated to a 100ft tower for outdoor RADAR experimentation where the collected calibration tables were successfully applied on the system. This paper will discuss challenges and successes in measurement of digital arrays within the compact range environment.
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.
Compact omnidirectional antennas are highly sought for a multitude of present-day wireless applications such as smart car keys, radio frequency identification (RFID) tags, tire pressure monitoring system, hand-held communication devices, and high-temperature harsh-environment wireless sensors. This paper discusses the performance and the unique challenges in measuring the radiation performance of a compact (~1/25th to 1/10th of a wavelength) helical and microstrip combined structure operating as a normal mode helical antenna (NMHA) around 300MHz. The helical wire structure (27-turn, 37mm high and 6.2 mm wide) is connected to the end of a 50 Ωmicrostrip line fabricated on 1.5 mm thick FR4 substrate. The microstrip line provides a ground plane to the helical structure, serving as an integral part of the radiating element. A tiny 1:1 balun transformer was used to partially decouple the integrated NMHA from the external sheath of the coaxial cable connected to a vector network analyzer, thus allowing proper NMHA impedance measurement. The NMHA S-parameters were simulated on two different platforms, ANSYS-HFSS and WIPL-D Pro, and compared to the frequency of the measured structures, with all simulations and measurements agreeing within 3.5%. Varying the length of the ground plane associated with the microstrip line from 13 mm to 76 mm resulted in the decrease of the measured NMHA operational frequency by 3.2%. The measured impedance of the fabricated NMHA (including the balun) was close to 50 Ω for the 51 mm long line without the need of additional matching circuit. The measured transmission loss for two identical antennas (each 26 cm3) placed about 1 m apart was 22 dB. This performance is comparable or better than the coupling between much larger antennas currently used in harsh environment power plant applications, such as suspended plate antennas (42,500 cm3) or planar inverted F-antennas (11,800 cm3) operating around the same frequency. In addition, the proposed NMHA structure can be implemented using substrates and wires capable of operation at temperature above 300 °C, which constitutes an appealing solution for high-temperature harsh-environment applications such as those found in industrial machinery, metallurgic industry, power plant boilers, and turbine engines.
Abstract— A 2021 AMTA paper[1] introduced a 3D holographic filtering algorithm optimized for the planar near-field (PNF) geometry. This filter has been shown to have an excellent combination of AUT-signal preservation, stray-signal rejection, and processing speed. It requires only the sampling of a conventional PNF measurement, along with a specified 3D boundary surrounding all of the AUT’s possible radiating sources. The 2021 paper[1] suggested some topics for further investigation, specifically the optimal Z spacing through the 3D hologram and the X- and Y-widths of the blanking window’s tapered extension, and those are investigated here. This paper also explores the combination of filtering and probe correction, since the measured convolution of probe and AUT spatial distributions will be wider than that of the AUT by itself. Finally, additional comparisons are made to the more traditional spherical-mode-truncation approach with different synthesized constellations of stray-signal radiators. Keywords: modal filtering, spatial filtering, holographic filtering, stray signals, planar near field [1] S.T. McBride, P.N. Betjes, “Holographic PNF filtering based on known volumetric AUT bounds,” AMTA 2021, Daytona Beach, FL.
A compact ultra-wideband (UWB) ground penetrating radar (GPR) antenna has been developed for extraterrestrial subsurface sensing from 130 MHz to 2000 MHz continuously. The antenna was designed as a payload of a new cube rover developed by Astrobotic for lunar exploration. The maximum payload dimensions are 58cm x 20cm x 18cm (LxWxH). The lower frequency bound of 130 MHz allows for deeper penetration depth and the upper frequency bound of 2000 MHz provides a large bandwidth for achieving a high depth resolution. Designing such compact UWB GPR is challenging for many reasons: small antenna volume relative largest wavelength, wide operating frequency range, minimization of clutter from antenna and surface reflections, and maximization of the transmission of radar signals through the air-soil interface. The proposed antenna design adopts the dielectric loaded horn-fed bowtie dipole design. The antenna operates primarily from the dielectric-loaded horn section at frequencies above 400 MHz where the ULTEM 1010 material is used to load the horn thereby increasing its electrical size and controlling the radiation patterns. Below 400 MHz, this antenna functions as a folded dipole where the entire 3-D conducting arms and the conducting top plate contribute to the antenna operations. Special RF choke designs are also developed to suppress undesired cavity modes which are excited in the cavity behind the feed position. In addition, a wideband microstrip balun circuit board was designed and integrated directly on to the antenna arm for connecting the antenna’s balanced 120 ohm port to a 50 ohm coaxial connector without being affected by high-G vibrations and shocks during typical rocket launches. An antenna prototype was fabricated, and its antenna performance was measured with a good agreement with simulation predictions. This paper will describe the antenna specification, operating principles, as well as measurement and simulation performances.
During the last few years, the increasing use of wireless equipment has raised the quantity of radiation energy to which human bodies are exposed. For this motivation, an evaluation of the Specific Absorption Rate (SAR) for persons is fundamental to determine the amount of radiation that human tissue absorbs and to comply with human safety regulations. Standard testing methodology consists of measurements with robot-based scalar/vector near-field probes and post-processing. The probe acquires the field level inside a phantom filled with liquid to ensure compliancy with certification standards. Although accurate, this technique could be extremely time-consuming, especially with the arrival of new frequency bands, new standards (5G, Wi-Fi 7), and the requirement to test different beams directions for beam-forming MIMO configuration. Another testing methodology, used especially for pre-assessment, consists of a full simulation of the radiator in the presence of the phantom, but this implies that the full wave model of the device is available, and this is rarely the case. To overcome the above-mentioned limitations, an alternative technique presented in this paper can be applied. This is based on a standalone measurement of the radiating device, that is post-processed with the method of the equivalent currents to generate NF source (in the form of a Huygens box). The SAR values inside the phantom are assessed using a non-invasive procedure with the assistance of a numerical simulation tool. Such method represents a fast procedure for pre-analysis of device prototypes, allowing to perform the conclusive testing only on the final device to verify the compliance with the regulations. The methodology is here experimentally validated on a dipole radiating in a presence of a phantom model by comparison of numerical simulated data and a reference measured data by a MVG ComoSAR V5 system.
Antennas are used in virtually all wireless, communications and radar systems. As key elements in these applications, antennas play a crucial role in determining the system’s overall performance. This makes accurate antenna characterization essential for any wireless application. Traditionally, electrically large antenna ranges are not equipped to perform return loss measurements and thus a separate benchtop vector network analyzer (VNA) setup is required for measuring reflection coefficient or VSWR of an antenna under test (AUT). In this paper, we demonstrate the two-port S-parameter measurement capability of the NSI-MI Vector Field Analyzer™ (VFA) and how it can be used to integrate return loss measurements in an antenna range. The VFA’s ability to perform multi-channel vector (amplitude and phase) electrical measurements and its long cable support using remote mixer interface (RMI) modules makes it well suited for antenna characterization, especially in electrically large measurement systems. For this experiment, we selected three known millimeter-wave components as devices-under-test (DUT) and measured the S-parameter matrix for each. These WR-10 band measurements were made using the VFA with Virginia Diodes VNAX frequency extension modules. Results are compared with Keysight’s N5225A performance network analyzer (PNA) using the same set of frequency extension modules for verification. Millimeter-wave S-parameter measurements taken on VFA and PNA setups for all DUTs are compared based on three factors: Repeatability, reproducibility, and measurement comparison. The variations between successive measurements are presented in graphical form to compare repeatability of both instrument setups. Reproducibility results are compared to show the difference between independent repeat measurements taken on both instrument setups. Error distribution comparison is presented for reproducibility test data to compare the measurement variations contributed by random sources for both instrument setups. Measurement comparison result shows the total difference between independent VFA and PNA measurements taken for each DUT. Keywords — Millimeter wave measurements, Scattering parameters, Calibration, Network Analyzers, Antenna measurements
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.
Over the past decades, near-field (NF) measurements have been established as a reliable alternative to direct far-field (FF) or compact-range measurements for the verification of radiation properties of antennas. Quantities of interest typically include the FF characteristic obtained by means of an NF FF transformation (NFFFT), which is a computational post-processing step applied to the NF data. Common NFFFTs work with time-harmonic data and require the acquisition of magnitudes and phases of the NF samples with respect to a common reference signal. In other words, classical NFFFTs require the observed magnitude and the observed phase data to be drift-free during the time span of the complete measurement. With increasing measurement frequency and exposed or complex measurement setups in uncontrollable environments, e.g., as encountered in outdoor NF antenna measurements with unmanned aerial vehicles (UAVs), phase stability quickly becomes a limiting factor. Therefore, nonlinear phaseless NFFFTs have been developed that do not require any phase information, which, however, heavily rely on accurate and globally consistent magnitude information and are notorious for their unreliable behavior. Recently, a linearized and reliable NFFFT operating on locally consistent, i.e., relative, phase information has been reported. By using local phase differences within the NF data, the method becomes immune to phase drifts of the reference signal. However, in real-world measurements in uncontrolled environments, drifts in the measured power or magnitude may occur as well, e.g., caused by temperature variations during UAV flights, which render common phaseless NFFFTs useless. In particular, this prevents the use of the otherwise reliable linearized transformation. We investigate NFFFTs requiring a variable degree of global synchronization. In particular, a linearized transformation utilizing only relative, i.e., locally synchronized, information, both in magnitude and phase, is presented. It is shown that the transformation yields similarly accurate results as transformations employing global data, while being immune to magnitude and phase drifts. Furthermore, we compare the overall benignancy of a complete set of retrieval problems: completely phaseless, magnitudeless and mixed relative/global magnitudes and phases. Transformation results for simulation data illustrate the accuracy and suitability of the transformations with relative data, even for electrically large problems.
Motivation and background: The increasing sophistication of wireless communication systems necessitates accurately designed test environments such as anechoic chambers. The minimum achievable level of noise and interference in such test environments is essentially determined by the reflectivity of the absorbers installed, emphasizing the importance of characterizing their scattering behavior under realistic test conditions. In order to improve the modeling of absorber-lined anechoic chambers e.g., based on ray-tracing methods, a profound understanding of the relationships between the geometrical (e.g., pyramidal or convoluted shapes) and material properties (complex-valued dielectric permittivity) and the frequency- and angle-dependent reflectivity of the absorbers is needed. Objectives and methods: The angle-dependent scattering off convoluted microwave absorbers at normal and oblique incidence was investigated at frequencies between 2 GHz and 18 GHz. Based on measured permittivity values, a unit-cell model was constructed to compute the angle-dependent reflectivity of absorbers of different shapes. To verify the model, the scattering off such absorbers was measured in a bi-static setup at different angles-of-incidence up to 60 degrees, and compared to the numerical results. In addition to the convoluted absorber geometry, pyramidal and wedge-shaped absorbers were studied, in order to analyze the influence of the absorber geometry on the reflectivity while maintaining the same material properties. Results and conclusions: The numerical results of the convoluted absorbers agreed well with the measured reflectivity, thus validating the numerical model. The results revealed an increase of the reflectivity at angles-of-incidence above 45 degrees, in accordance with expectation. Compared to the convoluted geometry, the pyramidal and wedge absorber shapes showed reflectivity values about 10 dB lower, for frequencies at which the electrical size of the absorbers exceeded unity. Together with the results of previous studies, these findings provide important ingredients for a comprehensive database of the angle- and frequency-dependent absorber reflectivity, from which a consistent ray-tracing modelling of anechoic test environments can be derived. This research has been funded by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) under the grants HE3642/14-1 and BO4990/1-1 (Electromagnetic modeling of microwave absorbers - EMMA; Project-No. 418894892).
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.
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.
Plane wave generator (PWG) for Over The Air (OTA) characterization of beamforming millimeter wave devices, provides an attractive solution comparing to conventional measurement techniques (Compact Antenna test Ranges (CATR) and Far-field chambers). MVG’s Plane wave generator for 5G NR FR2 applications ([1]-[4]) is an innovative tool which permits the user to measure the radiating elements with low to medium directivity radiation characteristics with excellent precision. Conventional CATR systems are not suited for stationary DUT (with / without person) measurement scenario. In this paper, experimental results are presented for a dual-polarized PWG system, covering the 3GPP bands n257, n258 and n261 (24.25-29.5 GHz). System measurement results show good comparison with simulations and measurements of the PWG alone. Another advantage of PWG presented here, is that we can modify the size of the QZ. Results from a pre-production unit for a 15cm QZ shows amplitude variation of less than ±1 dB and achieve more precision for smaller DUT. Measurement results from the pre-production unit with a quiet zone of up to 38cm sphere diameter, show amplitude variations of less than ±2dB. This variation is compatible with the DUT + phantom or human measurement application. Pattern results for Antenna Under Test (AUT) with low to medium directivity (6dBi up to 17dBi) compare well with simulations and measurements from other systems. For a given AUT, the impact of different positioning mast is also evaluated. Excellent stability of patterns, when the AUT is placed at different positions inside the QZ, is observed. These results confirm that the dual-polarized PWG system presents an attractive solution for FR2 characterization of low to medium directivity radiating elements.
Progressing towards highly automated vehicles, radar systems have been developed into reliable assistance systems of environmental perception for a wide spectrum of mobile applications in air, on sea and rails, and especially on roads. This success as well as further improvements necessitate the precise characterization of radar objects with radar cross-section (RCS) measurements throughout the manifold parameter space, including frequency, aspect angles or even illumination and observation angles in bi-static radar constellations. According to the IEEE RCS standard 1502-2020, parasitic effects from ground reflections have to be taken into account in the test setup in almost all RCS measurement systems. In ground-plane ranges, multipath signal propagation is even considered intentionally. In this paper, the influence of ground reflections on bi-static radar measurements has been investigated both analytically and experimentally. A geometry-based analytical model was applied to calculate interference and the resulting small-scale fading of the electric field strength at the receiver. The geometry consists of independently arranged transmitter, receiver, and scatterer. The model includes antenna crosstalk, ground reflections for different relative heights of transmitter and receiver, and the scattered signal contributions. As a result, six paths are considered in terms of their time delays and phases, resulting from the classical two-way propagation model in a point-to-point link plus the four-way radar propagation model including ground reflections. The model yields interference gains between 0 and 4, where the maximum value is uniquely obtained at equal distances between transmitter and scatterer, and between scatterer and receiver, respectively. The variations of the bi-static angle lead to further fluctuations, which confirm to expectation and will be described in the full paper. The analytical model was validated with bi-static radar measurements in a semi-anechoic chamber with a metallic ground floor. As a canonical radar target, a metal sphere was measured in the frequency range between 1GHz and 10GHz at different heights and distances. The measurement results confirm the analytical model and provide the basis for further extensions of practical relevance, e.g., the reflectivity parameters of the ground (e.g., dry and wet road surfaces). Funded by: Federal Ministry of Education and Research (BMBF), grant number 16ME0164K
This paper presents a selection guide for metal mesh based on shielding effectiveness and optical visibility requirements. Concepts of mesh sizing, wire diameter, metal type, opening size, metal color, and mesh patterning are discussed. The guide provides a detailed explanation of factors that contribute to the shielding performance and optical transparency of various mesh options. Metal mesh has a range of applications in the microwave, antenna, and EMC industries as they are particularly suited for protecting chamber viewing windows. Shielding effectiveness performance is dependent on the mesh sizing, wire diameter, and opening size, where the dimensions of the apertures directly influence the suitability of the mesh for a given frequency range. Finer mesh yields superior shielding, but with limited optical visibility. For this reason, the necessity for finding an optimal tradeoff between shielding performance and optical properties arises, where the selection guide in this paper can be used to make an informed decision. For ideal optical properties, the mesh sizing is critical since it determines the visibility through the material. Mesh layering and alternative optically transparent shielding solutions like RF film are also compared. Although layering of metal mesh offers additional shielding, the layering is associated with a reduction in visibility due to the mesh density and patterning from the Moiré effect. Alternatives like RF film can offer highly transparent solutions, but with inferior shielding effectiveness than metal mesh. This paper provides a quantitative analysis of shielding effectiveness results based on mesh parameters and aperture dimensions. The appropriate frequency ranges for the various metal meshes are also calculated. Using the selection guide presented in this paper, the user is enabled to make an educated technical decision on the metal mesh best suited to satisfy the shielding effectiveness and optical visibility requirements for the application.
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.
Motivation and background: Wireless communications are key for connected and automated driving. Beyond automation levels that require the presence of a driver, tele-operated driving has been receiving more attention recently. For such applications, gapless wireless coverage and stable connectivity are required, enabling a reliable exchange of data like control information or high-definition maps even under poor radio wave propagation conditions. Therefore, extensive testing of the link stability of mobile wireless communication systems is necessary, especially in challenging scenarios that are susceptible to link failure. Objectives and methods: We propose the emulation of relevant corner-case scenarios for virtual-drive testing, consistently and reproducibly derived from field-operational tests on public roads. The available data rate of a LTE link near mobile cell edges is considered a relevant test metric, since the link is expected to be particularly susceptible to failure under such conditions. We performed field-operational tests on two different test tracks, in order to prove the reproducibility and consistency of the proposed case. We have emulated the scenarios in a wired setup under realistic conditions using a communication tester and an interference generator. Power-related key-performance indicators like RSRP and SINR as well as the achievable throughput were systematically studied under laboratory conditions. Results and conclusions: The region around cell edges could undoubtedly be identified as a challenging scenario for automotive LTE communications, leading to a reduction of the data throughput by a factor of 5, on average, compared to the maximum data rate during a test run. This effect could be consistently observed on both test tracks. The emulation of wireless link parameters in such corner-cases reproduced the physical parameters of the field-operational test results very well. Changes of the data rate could be associated with the channel quality indicator. Approaches to improve the emulation of the drive tests is in the focus of future work. However, given the simplicity of the test setup, it represents a sound basis for refined over-the-air tests.
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.
Near-field (NF) measurements is considered as a very accurate and versatile antenna testing technique. It became widely used as a preferred measurement technology in antenna measurement systems about four decades ago. Today, hundreds of near-field antenna test facilities are installed worldwide. The IEEE Std 1720™ “Recommended Practice for Near Field Antenna Measurements” is specifically dedicated to near-field antenna measurements. It therefore complements the IEEE Std 149-1979™ “Standard Test Procedures for Antennas” which describes general antenna measurement procedures. The Std 1720™ was originally approved in 2012 as a completely new standard by the IEEE Standards Association Standards Board. It is highly relevant for users performing NF antenna measurements but also the design and evaluation of NF antenna measurement facilities. After 10 successful years, the standard expires this year and will no longer be an active standard under the IEEE. A revision is required to update the document with new developments and technologies that have matured since the first edition. This is the scope of project P1720 that was approved by IEEE-SA in 2019 to undertake “minor revision” of the current standard. A Working Group (WG) of the Antennas and Propagation Society Standards Committee (APS/SC) has been formed for this task. The WG is transversal, with users and experts of the near field measurement field and consist of approximately fifty dedicated volunteers from industry, academia, and government. This paper gives an update on the running activities and discusses the suggested changes to the standard.