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In the 2013 revision of the IEEE Standard for Definitions of Terms for Antennas [1], multiple new terms were added to describe active antenna systems. One such term is receiving efficiency, which was added to describe the behavior of either a passive receiving antenna or an active receiving antenna system. The definition of receiving efficiency contains other new terms such as isotropic noise response and isotropic noise response of a noiseless antenna. These new terms and definitions may cause some confusion for individuals responsible for antenna design and measurement. We attempt to demystify a few of the terms added to IEEE Std 145-2013, especially those terms that relate to receiving efficiency. In addition, we propose a measurement technique for measuring the receiving efficiency of an active receiving antenna system.
After a five-year renovation of the National Institute of Standards and Technology (NIST) Boulder, CO, antenna measurement facility, the Antenna On-Axis Gain and Polarization Measurements Service SKU63100S was reinstated with the Bureau International des Poids et Mesures (BIPM). In addition to an overhaul of the antenna facility, the process of reinstatement involved a comprehensive measurement campaign of multiple international check-standard antennas over multiple frequency bands spanning 8 GHz to 110 GHz. Through the measurement campaign, equivalency with 16 National Metrology Institutes (NMIs) and continuity to several decades of antenna gain values was demonstrated. The renovation process, which included implementing new robotic antenna measurement systems, control software, and data processing tools is discussed. Equivalency results and uncertainties are presented and compared to checkstandard historical values.
This paper presents a new test procedure to asses and validate key performance indicators for NGSO antennas, and serves to introduce said methodology to the antenna measurement community to foster a discussion on future evaluation procedures for modern day ground segments. Beyond introducing the proposed test methodology we also present results highlighting the actual accuracy of a UAV based measurement system enabling the proposed measurement procedure. The paper is intended to be viewed as an initial proposal for a qualification methodology.
This paper extends the time-domain gated response isolation scheme for full polarimetric calibration with a modified Thru-Reflect-Match procedure for network analyzer selfcalibration where precise knowledge of the metrology standards is not required. Cross-polarization contributions from the measurement setup are neglected to simplify the procedure. A simulated cascade analysis is included to demonstrate the relative scattering parameter error of the sample under test when the measurement setup cross-polarization level is neglected. The featured calibration analysis leverages a 4x4 scattering parameter matrix notation to capture the polarimetric scattering at each cascaded stage and develops a 16-term error correction factor model to account for cross-polarization scattering contributions from the measurement sample. Finally, a wire-grid polarizer is used as a modified Match standard where a series of interrogations at multiples orientations, in combination with Thru and Reflect measurements, enables cross-polarized scattering channels to be characterized. This polarimetric self-calibration approach uses physically realizable metrology standards and accounts for all error terms for precision focus beam system measurements.
The IEEE Std 1720™, "Recommended Practice for Near-Field Antenna Measurements," serves as a dedicated guideline for conducting near-field (NF) antenna measurements [1]. It serves as a valuable companion to IEEE Std 149-2021™, "IEEE Recommended Practice for Antenna Measurements," which outlines general procedures for antenna measurements [2]. IEEE Std 1720 was originally approved in 2012 as a completely new standard by the IEEE Standards Association Standards Board. It holds significant importance for users engaged in NF antenna measurements and contributes to the design and evaluation of NF antenna measurement facilities. With its tenyear term coming to an end in 2022, the standard will no longer remain active. Nonetheless, a "minor revision" of the existing standard is in progress and is expected to be completed in 2023. The objective of this paper is to provide insights into the ongoing activities surrounding the revision and to explore the proposed changes. It aims to facilitate a discussion on the modifications to and their implications for modern NF antenna measurements.
The reflectivity of foam absorber materials is governed by the correct loading and mixture of carbon and other supplicants such as fire retardants. In order to assess the reflectivity of the absorbers various measurement setups are applied, each having different advantages and disadvantages in terms of frequency coverage and RF performance. The measurement setups are used both in the quality control (QC) as well as for product development. Especially for the product development case, it is important to understand limits of these setups as the lower the reflectivity gets, the more difficult it becomes to detect minute differences between different variants of the absorbers. For reflectivity measurements of microwave absorbers, the available dynamic range and calibration-quality of the setup plays a vital role in this respect. By determining the uncertainty of the measurement setups, a clear assessment can be made to the quality of the measurement and the product to insure consistent QC, as well as plan for the product development.
The IEEE Std P2816 recommended practice for computational electromagnetics applied for the modeling and simulation of antennas is currently being developed by the IEEE Antennas and Propagation Standards Committee (APS/SC), sponsored by the IEEE Antennas and Propagation Society (APS). The document provides guidance on the numerical modeling of antennas deployed in free space using commonly adopted computational electromagnetics (CEM) techniques such as the finite element method (FEM), the finite difference time domain (FDTD) method, the Method of Moments (MoM), the finite integral technique (FIT) and the transmission line matrix (TLM) method. Benchmark models and comparisons of numerical simulation results are included for potential users of the standard to better understand the uncertainties and limitations of these techniques. A biconical antenna was previously proposed as a benchmark model. The numerical simulation results showed a good overall agreement among the participating laboratories and against the analytical solution. Herein, a 5G New Radio (NR) FR1 ultrawide band (UWB) antenna is proposed as another benchmark model for the development of IEEE Std P2816. In addition to the comparison of the numerical simulation results obtained from the participating laboratories, the simulation results are confronted with preliminary measurement results.
The existing IEEE-STD 1128 on “Recommended Practice for RF Absorber Evaluation in the Range of 30 MHz to 5 GHz” was published in 1998. The standard has been referenced frequently and used as a guide for RF absorber evaluations. The document has several aspects which need updating, including the frequency range of coverage, requirements for newer test equipment, advances in test methodologies and material property evaluation, measurement uncertainty considerations, and absorber high power handling and fire testing requirements. The working group is divided into task groups and is in the final stage of collecting inputs from these subgroups. The next step is to consolidate the inputs and produce a draft standard for a wider distribution before being submitted for balloting. The subgroup contributions can be found on the IEEE imeetcentral website (https://ieeesa. imeetcentral.com/p1128). The sections which have received substantive updates include bulk material measurements, instrumentation, absorber reflectivity measurements, and power handling test. In this paper, we will provide some detailed discussions on the planned updates from these contributions. For areas which did not receive sufficient input, the working group plan to table those topics for future considerations.
This paper addresses the circularly-polarized (CP) gain uncertainty when using linearly-polarized feeds to obtain circular polarization in Compact Antenna Test Ranges. In particular, our emphasis is placed on quantifying the inaccuracy caused by deviations in amplitude and in phase of the two orthogonal linear measurements. This is of paramount importance especially for highly directive CP antennas operating at high frequencies in that the CP gain will be adversely impacted even by a small deviation from an ideal 90- degree rotation, as well as by a situation when the rotation may cause a slight boresight misalignment. To characterize the gain uncertainty, we look at ratio differences between the peak amplitude of the linear measurements, as well as cases when the phase shift of the two orthogonal linear measurements is no longer 90 degrees. The former is done through mechanical and electrical boresighting technique in the initial setting. The latter, which is the focus of this paper, is carried out through several case studies in practice mimicking some non-ideal 90- degree rotation settings.
With the event of integrated and multi-standard wireless links, phaseless antenna measurements are attracting more and more interest in research. Especially in the context of connected and automated driving, antennas, frontends, and digital signal processing units merge into telematic units and require new methods for performance evaluation in the installed state. The measurement of the phase diagram and the exact absolute positioning of electrically large antennas, i.e., antennas interacting with the car body, present challenges for safety-relevant applications and reliable test methods. This paper describes a way to determine the position of automotive antennas in the installed state with sub-wavelength precision from phaseless measurements. Realistic LTE uplink signals were used as test signals as they would be transmitted by an active device in a real-world scenario. The localization algorithm is based on orthogonal power measurements of the transmitted signal on a cylinder surface and a non-linear optimization. By comparison with a conventional localization based on spherical far-field data, an accuracy of the approach of less than 1 cm was achieved, which is less than λ/16 at the considered frequency of 1870 MHz.
Antenna measurement Intercomparison Campaigns represent a successful activity within the working group on antenna measurement of the European Association on Antennas and Propagation [1] since the group foundation in 2005. These campaigns, constitute an important resource for participating facilities to demonstrate their measurement proficiency, useful internally but also towards obtaining or maintaining official accreditations. In this paper we present the completion of a campaign involving a high gain X/Ku/Ka-band reflector, MVG SR40 fed by an MVG SH4000 Dual Ridge Horn. Preliminary results were shown in [2]. Results from seven facilities are compared through plots of gain/directivity patterns. The data is used to generate reference patterns and establish accurate gain performance data based on the uncertainty estimates provided by each facility. Statistical analysis of the measured data such as Equivalent Noise Level and Birge ratio of each measurement with respect to the established reference will also be shown.
Near-field far-field transformations (NFFFTs) are usually performed for time-harmonic fields. In cases where insitu antenna measurements are required and the antenna under test (AUT) is not accessible for specifically tailored test signals, the need for handling time-modulated fields arises. The shorttime measurement (STM) approach offers a way to deal with continuously modulated fields while a time-harmonic NFFFT can be employed. We present results of numerical simulations to demonstrate and characterize the STM approach for the case of a cylindrical measurement geometry as found in UAV-based antenna measurements. We further derive guidelines from the simulation results that describe the applicability of the STM for different measurement situations.
Earlier works have shown the benefits of imaging stray signals in a range with planar-scanner data. This paper discusses some additional tools that can be employed for stray-signal identification. Related range diagnostics are presented that employ Fourier spectral and holographic processing of 1D linear scans through the quiet zone. For the special case of a compact range, the interpretation of arrival angles from the paraboloidal reflector surface is explored. Measured data from multiple facilities are presented that were used to locate, quantify, and remedy the unwanted signals.
Full Probe Compensation (PC) techniques for Spherical Near Field (SNF) antenna measurements have recently been proposed and validated with success [1]-[4]. Such techniques allow the use of antennas with more than a decade of bandwidth as near field probes in most systems. The clear advantage is that multi-service/frequency measurements campaigns can be performed dramatically reducing the number of probes hence decreasing the downtime between two measurements. This is a highly desirable feature for modern antenna measurement applications such as automotive. The use of a dual-polarized probes further improves the measurement efficiency as two orthogonal field components are measured at the same time. The possible differences between the pattern radiated by the two ports of the probe should sometimes be considered to keep the overall measurement accuracy. The full PC technique objective of this paper accounts for generic dual-polarized probes and is validated for the first time. For this purpose, measurements of three monocone antennas from 450 to 6000 MHz performed with only one wideband (15:1) dual-polarized probe will be considered.
Prior literature in the subject area of far-field antenna measurements has demonstrated an extrapolation technique to isolate and correct the errors associated with nearzone proximity effects, specifically multiple reflections between the probe and the antenna under test (AUT), thus allowing measurements to be acquired at separation distances much shorter than the conventionally defined far-field criteria. A recent paper on this topic described a modern, indoor, far-field antenna measurement range specifically designed to support the traditional extrapolation technique while also incorporating high-speed RF instrumentation and advanced software control of a mobile probe tower. The automation of the traditional technique was emphasized, and the application focused primarily on X-band performance. Herein presented is an updated and more broadband approach which utilizes both amplitude and phase data to extend the implementation to frequencies in the UHF-, L-, and S-band. Optimized correction factors are generated for additional extraneous signals, most notably the effects of multi-path interference. Using the generalized three antenna measurement approach as highlighted in the original technique, measurement examples are provided for broadband antenna range horns, and the resultant far-field gain calculations are again compared to similar data extracted using traditional near-field scanning techniques.
The question of how to perform a nearfield antenna measurement in the presence of the air-sea interface is one that has been raised previously by the author[1]. When discussing spherical near field measurements various approaches have been proposed for addressing this problem, that are also applicable to measurements taken over a conducting ground plane. In this paper we shall discuss some of the practical challenges involved in data collection and measurement methods when performing this type of measurement. Examples shall be taken from both spherical nearfield measurements of simple sources along with single-point at-horizon measurements to examine the challenges associated with these approaches. A notional approach for measuring realized power gain at the horizon will also be discussed.
A signal source can introduce phase-measurement errors when its output crosses through internal frequency-band breaks. The source phaselock circuits in this band-break region sometimes report approximate phaselock before complete phaselock occurs. The result of this approximate phaselock is a minor error in the output frequency, which can lead to phase-measurement errors at the system level. The magnitude of the phase errors depends on the amount of frequency offset and the difference in electrical lengths between the measurement system's signal and phase-reference paths. If this behavior were deterministic, then the resulting phase errors might be tolerable. Unfortunately, it was found that the final settling time (measured in many hundreds of milliseconds) was not consistent, depended in part on the two specific frequencies surrounding the band break, became more confused if a second sweep encountered the band break before the first break had settled, and of course changed behavior if the frequencies were sequenced in reverse order or measured one at a time. The design approach described herein reduced to negligible the phase-measurement errors due to frequency errors in two large multioctave test systems. The approach relies on managing range transmission line lengths so that propagation time is sufficiently equal among the various signal and reference paths. Measured data are presented that show the advantage of the optimized system design.
A near-field scanner has been upgraded, maintaining mechanical hardware more than 65 years old and extending it with suitable computer control to enable an 8.9x1.6m^2 scanplane. Already in 1957 X-band phase accuracies within 3 degrees were reported (ref.1). The facility is computer controlled, with servo's to enable position and polarisation control and a Rohde and Schwartz network analyser in the loop. It is positioned in an area near the main workshop and runs proprietary software for control, acquisition and transformation. An old satellite antenna has been aligned as Antenna Under Test (AUT) and measured near 12 GHz. It was measured before as reported in (ref.2). The antenna is an engineering model of an antenna used on the OTS satellite in mid 80's. It has a few properties which are worthwhile to use for inspection, to enable to get insight into scanner properties and transformation results. Deviation between electrical and mechanical axis, low cross polarisation, orthogonal channels and specific input impedance can be mentioned as points to verify and to control with verification measurements exploiting symmetries and flip-tests, rather than ticking off in an 18-term error budget usually adopted. Direct gain measurements have been established. The probe can be selected, either an open-ended waveguide or a circular waveguide with annular corrugation as probe for instance. It involves related discussion of probe correction. The first results show acceptable information for the facility, with initial comparison to previous results for pattern and absolute gain. It has allowed to survey alignment, assess scanner control properties and assess microwave component properties - with interest into direct gain measurements. A short historical description for the facility (ref.1) and antenna precedes a main discussion of the followed procedures and obtained results for the AUT with related discussion.
The evolution of cellular communication technologies has been replicated by the automotive industry with modern vehicles being almost universally fitted, as a bare minimum, with a radio system, a cellular communication system and Bluetooth capability. Higher end vehicles have additional capabilities such as WiFi, GNSS, TPMS, smart keyless entry and smart start/stop feature. All these systems are highly integrated as part of the vehicle's infotainment unit and they must operate satisfactorily in a co-existing manner. Automotive wireless testing is currently facing several challenging aspects with one such aspect being MIMO OTA (Multiple-Input-Multiple-Output Over-The-Air) testing of the terrestrial cellular communication system of the vehicle. In this paper, we will examine the current approach for MIMO OTA testing in the 4G and 5G cellular environments and discuss various scenarios on how existing techniques can be adapted to support MIMO OTA testing in the automotive industry. MIMO OTA testing is typically carried out either using conducted testing techniques or using a Multi Probe Anechoic Chamber (MPAC); both these methods have their advantages and limitations and, to a certain extent, a degree of applicability to a very large article under test. This paper covers these two established MIMO OTA testing techniques and considers their applicability to the automotive MIMO OTA testing scene. Following on from this analysis and the challenges exposed herein, additional MIMO OTA test methods are put forward along with an assessment of how well they perform in an automotive test environment.
Phase uncertainty in antenna measurements introduces significant errors to the amplitude of the transformed pattern in Spherical Wave Expansion (SWE). To get a better understanding of the impact of phase errors, the measured phase error of a Low Noise Amplifier (LNA) is synthesized as a random phase error and subsequently added to the measured antenna patterns of three different antennas during the SWE. The resulting erroneous patterns are compared with the measured reference patterns and the error magnitude and probability distribution are studied. It is proven that the introduced errors to the transformed far-field patterns can be substantial. Furthermore, the relation between the antenna type and the error level and distribution is elaborated. The error level is different for the three antennas and the error level distribution is dependent on the mode spectra of the antennas.