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KRISS has introduced a 6-axis industrial robot into an antenna measurement system. This allows for various measurement applications and the continuous development of additional ones. Among these measurement applications, representative functions such as antenna gain measurement, material characteristics measurement, 3D field scanning, and RCS measurement are continuously being improved. The validity of the technology is discussed by comparing its results with measurements taken in a fully anechoic chamber.
This paper presents research validating the conductive resonant sphere creeping wave phase dilation discovered in high-resolution imaging presented at the 2023 Antenna Measurement and Techniques Association (AMTA), which focused on using a small resonant sphere as a test probe for assessing Radar Cross Section measurement accuracy [1]. The associated analysis uncovered a discrepancy in the creeping wave Standard Model physical pathlength around the sphere having less phase than required for resonance. This paper presents a new creeping wave phase dilation model resolving the phase difference and validating results with computational electromagnetic field predictions.
This paper investigates measurement uncertainty in a Reverberation Chamber (RC) within the lower FR2 bands (24.25-29.5 GHz). The study focuses on the impact of several factors contributing to RC measurement uncertainty, including finite sample size, polarization imbalance, and spatial non- uniformity. A series of 24 measurements were conducted using a horn antenna, known for its directivity in mmWave frequencies, varying antenna parameters such as height, orientation, position on the turntable, and polarization within a predefined chamber volume. The measurement uncertainty was evaluated by a method based on the standardized 3GPP and CTIA approaches, incorporating uncorrelated measurements and analyzing Pearson correlation coefficients between measurement pairs. An analysis of variance (ANOVA) was performed on the frequency-averaged power transfer function to identify the significance and impact of each variable on measurement variability. Additionally, the K-factor was estimated for each measurement set as part of the RC characterization, using an alternative approach to account for the turntable stirring effect. The findings highlight which variables most significantly influence measurement uncertainty, where the antenna orientation emerges as the most significant factor for the mmWave directive antenna setup.
In this paper we introduce a novel technique for the efficient production test and measurement of 5G, Massive MIMO array antennas for the purpose of verification, diagnostics, and fault detection that drastically reduces the number of measurements required and the associated acquisition time needed. The technique utilises compressive sensing and sparse sampling combined with a total variation measurement approach that enforces the requisite sparsity on the problem. In this paper, we compare this new spherical near-field total-variation based acquisition approach with the authors existing, analogous, planar technique. Extensive performance comparisons are presented which aggregate results across many test cases which is a necessity, and a consequence of the statistical nature of the compressive sensing technique that is imposed by virtue of the requirements of the Restricted Isometry Property (RIP). Crucially, this paper identifies and addresses a fundamental flaw within the application of many total-variation based methods and especially when used with the difference field between a reference antenna and a production test antenna. This extends the use of a novel analysis process that incorporates an l0 based minimisation strategy to overcome this problem thereby restoring the CS process to very nearly the levels of performance attained in our prior work.
We report a new class of wearable loop sensors for monitoring human kinematics (particularly, joint flexion angles) while overcoming limitations in the state-of-the-art. Previous studies have demonstrated the feasibility of these loop sensors using tethered connections to a network analyzer. In this work, we take a major step forward to demonstrate untethered operation for the sensor. To this end, transmitter and receiver boards are designed and integrated into the loops. The transmitter board sends a Radio-Frequency (RF) power of 5.68 dBm at 34 MHz upon a 50 Ω load, while the receiver board detects the power level and transmits the data to a nearby personal computer (PC) via Bluetooth. Flexion tests are conducted upon a tissue-emulating phantom to validate the setup. To quantify performance, we calculate the root mean square error (RMSE) between the estimated angle from our sensor and the gold-standard angle from a marker-based motion capture camera system, as well as Pearson’s correlation coefficient (ρ). The proposed sensor shows outstanding performance with an average RMSE of 0.670° and an average ρ of 0.99966. Overall, our sensor outperforms state-of-the-art wearable kinematic technologies by being highly accurate, seamless, lightweight, unobtrusive to natural motion, and reliable over time.
The need for fast and accurate measurement techniques for electromagnetic exposure from modern communication devices has increased since few years. The exposure metric for frequencies up to 10 GHz is the Specific Absorption Rate (SAR). The Link approach has been studied and validated since few years to evaluate the SAR for passive antennas and some active devices which can be controlled in terms of output power and have no automatic power adjustment mechanism. In this paper, we go a step further and apply the Link approach to measure the SAR for a commercial smart phone, where we have no a priori knowledge or control, over the power control mechanism, and the antenna position inside the phone. The measurements are done with a 10MHz bandwidth LTE signal communication, between a commercial smart phone, and the Radio Communication Tester (RCT) emulating a mobile Base Station. The E-field distribution and SAR values, computed from the Link approach, are compared to results from the same DUT measured with a legacy SAR (single probe with a robot and phantom) measurement system. The results show SAR values, within 2.8% (0.1dB) for 10g SAR, and -7.1% (-0.3dB) for 1g SAR (at 5mm separation between phone and phantom), between the Link and Legacy approach. The SAR values at 0mm separation distance are calculated using extrapolation, and the difference is 7.0% (0.3dB) for 10g SAR and -6.2% (0.28dB) for 1g SAR. Based on these results, it is shown that the Link approach is a faster alternative SAR measurement approach, applicable for pre-compliance, during early stage of development, and for post-production scenarios.
In modern integrated radar systems conventional antenna measurements are often impractical due to the lack of access to the antenna feed points. For frequency modulated continuous wave radars, the two-way radiation pattern can be characterized with a reflector while utilizing the integrated transmit and receive module. However, some post-processing steps are required for this measurement method to obtain the frequency-resolved radiation characteristic. This paper takes a closer look at the fast Fourier transform (FFT) and inverse FFT with the associated window functions and the necessary range gating including zero-padding based on simulations. A sufficiently wide range gating is necessary to reconstruct the frequency resolution of the antennas correctly. Yet a trade-off between the required wide range and the filtering of mutual coupling and reflections from the environment has to be made in the case of real measurements. Moreover, depending on whether a frequency in the center or at the edge of the chirp is to be reconstructed, different window functions provide the most accurate result.
The application of a series of interconnected single-axis motion controllers distributed throughout an antenna measurement range has some important advantages when compared to multi-axis controllers that must reside in a central control room. The technologies used for distributed real-time control based on the Ethernet for Control Automation Technology (EtherCAT) standard are discussed, as are advantages and tradeoffs to be considered. The greatly reduced requirement for signaling between the control room and the remote axes reduces cost in system design and manufacturing. In practice, the shorter electrical signal runs can enhance electromagnetic interference (EMI) performance, noise immunity and safety.
This paper presents a study on the performance of GNSS antennas at various vehicle positions. Simulations and measurements were conducted in the L1-Band with and without an additional ground plane. The results were evaluated in terms of Right-Hand Circularly Polarized (RHCP) gain, axial ratio, and accuracy at different frequencies and positions. Real-world measurements using a ublox receiver were performed to validate the simulation results. The findings provide insights into the optimal placement of GNSS antennas in vehicles to enhance signal reception and reliability.
Over the past two decades, many measurement facilities have been involved in various international comparison campaigns led and supported by the European Association on Antennas and Propagation (EurAAP) working group (WG) on measurements (WG5). Its activities cover various areas of antenna measurements. These activities play an important role for the documentation and validation of laboratory proficiency and competence, helping to improve the antenna measurement procedures/protocols in facilities and standards such as ISO 17025, IEEE 149, IEEE 1720. The analysis and data elaboration have promoted discussions among the antenna measurement community experts and have led to modernization of comparison techniques. This paper highlights some selected EurAAP WG5 activities including, for example, international antenna measurement intercomparisons, self-assessment measurements of facilities, outreach collaborations and outcome disseminations (e.g., revisions of international standards for antenna measurements).
The aim of this research is to understand modeling techniques tailored specifically for low electrical conductivity materials, such as e-threads (σ~104 to 106 S/m) and other conductive polymers (σ < 104 S/m), for a wide range of antenna design applications (e.g., implantable antennas, flexible wearable antennas, and more). Commercial datasheets for such materials primarily report DC conductivity data. However, it has long been reported that conductivity of these materials exhibits frequency dependence, with notable increase in losses at higher frequencies, attributed to phenomena like surface roughness and skin effect. Our study involves a systematic exploration of diverse materials suitable for modeling low-conductivity scenarios, leveraging the capabilities of CST Microwave Studio. This involves the usage of various numerical solvers for analysis, with a goal to optimize antenna design in free-space as well as in proximity to the human body. Our analytical framework encompasses not only the evaluation of Radio-Frequency (RF) parameters such as return loss, gain, and antenna efficiency, but also extends to encompass system-level performance metrics, such as computation time and memory requirements. Overall, the proposed approach enables the identification of the most suitable modeling approach for antennas fabricated via low-conductivity materials, empowering near real-world simulation results.
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 1720-2012 was approved in 2012 as a completely new standard by the IEEE Standards Association Standards Board (SASB). It holds significant importance for users engaged in NF antenna measurements and contributes to the design and evaluation of NF antenna measurement facilities. A revision of the existing standard is nearing completion and is expected to be completed in 2025. The objective of this paper is to provide insights into the ongoing activities and to explore the proposed changes. It aims to continue the discussion on the modifications to the standard and their implications for modern NF antenna measurements.
One of the major contributions to the measurement uncertainty of antenna measurements are multiple reflections between antenna under test (AUT) and probe antenna. In the case of spherical near-field (SNF) measurements, multiple reflections are typically estimated and compensated for by conducting full SNF measurements at different radii and averaging the transformed far-field results. However, the need for several measurements leads to a multiplication of the measurement duration, and subsequently to an increase in costs. Another option is to increase the measurement radius, which might not be possible depending on the positioning equipment. Therefore, a technique to reduce multiple reflections between AUT and probe antenna by intentionally tilting the latter is presented. The technique is evaluated with a robotic antenna measurement system, the flexibility of which allows to almost arbitrarily tilt the probe antenna and perform a spherical measurement in this tilted configuration. It is shown that the magnitude of the reflections can be reduced significantly with this approach, even for small tilt angles. A comparison with the conventional averaging technique indicates that the presented approach reduces the error to a similar level, but at a fraction of the measurement time.
Radomes are structures or enclosures designed to protect antenna and associated electronics from the surrounding environment and elements such as rain, snow, UV light, and strong wind while at the same time not impacting the performance of the antenna. In some cases, radome designs include frequency selective surfaces (FSSs) embedded within the inner, outer, or intermediate interfaces of the radome. When properly designed, the FSS embedded radome structure can enhance the performance of an antenna system by filtering out unwanted frequencies. The design of Radomes, especially those containing multiple layers and curved frequency selective surface (FSS) elements, are extremely complex, with the modeling and simulation of these systems taking days and even weeks to complete. In this paper, we present advanced computational tools for fast and accurate simulation of the FSS embedded radomes using characterized surfaces. A detailed study on different FSS elements for their frequency response of the reflection and transmission coefficient behavior is also presented. Simulations are performed to study the effects of insertion losses, boresight error and effect on the antenna side lobes. Computational resource comparisons for simulations of actual structure of the radome versus those simulations using characterized surfaces are presented.
This paper presents an open-source framework for collecting time series S-parameter measurements across multiple antenna elements, dubbed MPADA: Multi-Port Antenna Data Acquisition. The core of MPADA relies on the standard SCPI protocol to be compatible with a wide range of hardware platforms. Time series measurements are enabled through the use of a high-precision real-time clock (RTC), allowing MPADA to periodically trigger the VNA and simultaneously acquire other sensor data for synchronized cross-modal data fusion. A web-based user interface has been developed to offer flexibility in instrumentation, visualization, and analysis. The interface is accessible from a broad range of devices, including mobile ones. Experiments are performed to validate the reliability and accuracy of the data collected using the proposed framework. First, we show the framework’s capacity to collect highly repeatable measurements from a complex measurement protocol using a microwave tomography imaging system. The data collected from a test phantom attain high fidelity where a position-varying clutter is visible through coherent subtraction. Second, we demonstrate timestamp accuracy for collecting time series motion data jointly from an RF kinematic sensor and an angle sensor. We achieved an average of 11.8 ms MSE timestamp accuracy at a mixed sampling rate of 10 to 20 Hz over a total of 16-minute test data. We make the framework openly available to benefit the antenna measurement community, providing researchers and engineers with a versatile tool for research and instrumentation. Additionally, we offer a potential education tool to engage engineering students in the subject, fostering hands-on learning through remote experimentation.
This paper presents a novel design for a multi-probe antenna array for continuous measurement in a planar near- field system. This design reduces scanning time while maintaining accuracy compared to conventional methods used in near-field planar systems. The work introduces the design of the irregular probe array and discusses its trade-offs and functionality. It includes a comparison of the results from the two methods mentioned and analyzes the time durations associated with each approach. Additionally, the paper provides projections based on previous data to estimate scan durations for a large number of sampling points, considering the impact of the velocity of the linear positioners.
Free space material measurements illuminate a material or component with wave propagating through space. Algorithms for inverting intrinsic properties or thickness from free space measurements usually assume an ideal plane wave. This is an approximation because a typical incident beam is finite in extent and comes from a nearby aperture. In reality, the beam consists of a distribution of plane waves around the propagation direction. Typically, the illumination spot is minimized to measure different areas of a material and characterize homogeneity, or because the component itself is limited in size. A smaller spot leads to a wider distribution of plane-waves, which causes an effect called space loss, where the illuminating beam spreads as it travels. An ideal plane wave does not have space loss, so the plane-wave assumption results in systematic error when space loss is present. This paper derives a correction for the space loss phenomenon and applies it to thickness inversions used in microwave spot probe measurements. The correction is demonstrated on commercial microwave probes and quantified with a series of computational electromagnetic simulations. These calculations are discussed in terms of microwave mapping of radomes to measure performance and establish their compliance with design specifications.
The IEEE Std 149-2021TM recommended practice for antenna measurements was recently revised by the IEEE Antennas and Propagation Standards Committee (APS/SC), sponsored by the IEEE Antennas and Propagation Society (AP-S). The document represents a major revision of IEEE Std 149-1977TM. It describes the procedure for the measurement of the transmitting and receiving properties of an antenna that is assumed to be a passive, linear, and reciprocal device. Among different topics addressed, it provides guidance about the antenna range design and evaluation. To complement this document, an international antenna measurement campaign was launched in an aim to provide an example of measurement that may be expected when applying this standard. A 5G New Radio (NR) ultrawide band (UWB) antenna was selected for this measurement campaign.
Industrial robotic arms offering high speed, precise positioning repeatability, and a high degree of freedom in motion, are an attractive alternative positioning solution for supporting a wide variety of scan geometries using a single antenna measurement system. For multi-function and production antenna measurement applications, this makes them a cost-effective solution compared to custom designed positioner stack-ups. However, motion is not the only consideration when implementing a multi-functional measurement system. The RF system design needs to be equally flexible to accommodate different measurement topologies and operating modes. Ideally, the solution should be flexible enough to also provide a clear upgrade path to accommodate future requirements. This paper discusses the use of commercial modular multi-port Vector Network Analyzer products in the implementation of a distributed RF system for a 14-axis robotic antenna measurement system that supports multiple antenna measurement geometries with minimal manual reconfiguration. This novel RF system design has the capability of simultaneously measuring multiple antenna test ports and can be easily reconfigured to support a variety of measurement configurations and other applications.
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.