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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.
We present a bench top demonstration of dropped-channel polarimetric compressive sensing to recover range profiles of a simple scene. Four antennas (H and V transmit and H and V receive) are connected to an arbitrary waveform generator and digital oscilloscope with programmable attenuators and phase shifters inline to control crosstalk. Range profiles of the scene are generated for three measured channels; the fourth is reconstructed from information imbedded in crosstalk using basis pursuit denoising. Reconstructed range profiles are shown to agree with measurements of all channels obtained without crosstalk contamination. Thus, the bench top setup demonstrates the potential use of dropped-channel polarimetric compressive sensing to reduce data storage and transmission burden while preserving full pol information.
The impact of receiver internal leakage on planar near-field measurement uncertainty is significantly influenced by the selection of near-field parameters. Understanding how specific scan parameters affect the far-field leakage level is essential for effective mitigation. This paper establishes quantitative relationships between near-field parameters and the far-field peak amplitudes of both leakage and the antenna under test (AUT), as well as the mean noise level in the far-field pattern, based on empirical results. Systematic scans were performed by altering only one or two specified near-field setup parameters per measurement, and graphical comparisons are provided. Practical approaches for mitigating receiver leakage are demonstrated through a case study involving receiver leakage on a planar scanner with a maximum scan area of 3.6 m x 3.6 m (12 ft x 12 ft). Additionally, a method for estimating the far-field receiver leakage level relative to the beam peak is discussed.
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.
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.
The measurement of active devices or Active Antenna Systems (AAS) necessitates the assessment of transmitter and receiver characteristics, such as radiated power, sensitivity, and occasionally data throughput. The AAS transmit and receive properties can be fully characterized by evaluating two spatial power quantities. Equivalent Isotropic Radiated Power (EIRP) when the AAS operates as a transmitter, and Equivalent Isotropic Sensitivity (EIS) when it functions as a receiver. This testing often requires an Over-the-Air (OTA) measurement setup and is relatively simple to perform when the measurement distance is sufficient for both the probe and AAS to be in the far field. For physically and electrically large AAS’s, this assumption can be hard to satisfy. This paper explores techniques for assessing spatial-directional transmitted and received power-related performance metrics of active devices using spherical near field measurement techniques. This approach can be complemented by phase recovery techniques to enable accurate NFFF transformation. The presented method is validated by experiments on a suitable validation mockup.
In this paper, the Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS) of Narrowband Internet of Things (NB-IoT) over Non-Terrestrial Networks (NTN) in the Anechoic Chamber (AC) are investigated. The following contributions are presented. Firstly, for the first time based on authors' best knowledge, this paper presents the Over-the-Air (OTA) TRP/TIS performance of NB-IoT NTN in the AC. Secondly, detailed analysis including test repeatability, measurement uncertainty, and test time etc. are given as well. The early exit algorithm for NB-IoT TIS based on Chi-Square distribution is investigated, and significant improvements have been found from the test results. Thirdly, various key NB-IoT NTN specific parameters, such as Round-Trip Time (RTT), Doppler shift, signal fading, and others have been discussed too. For TIS, we use 2 different RTT configurations (0 ms and 255 ms) to perform the tests, and give the corresponding analysis. Finally, some suggestions are being proposed for the future test methodology developing.
We present on a novel gain extrapolation antenna range, the Compact Homodyne Extrapolation System (CHEXS), that can achieve absolute antenna gain measurements with uncertainties of +/-0.1 dB or better with as few at 10 data points and is significantly more compact, up to six times shorter than conventional gain extrapolation ranges. This compact gain extrapolation range achieves these beneficial attributes by measuring the homodyne signal that occurs naturally between two directional antennas that often exhibit strong third order mutual coupling at close proximity. The design and operation of the CHEXS is presented along with gain measurements of NIST reference standard gain antennas which are shown to be equivalent to those obtained using a conventional gain extrapolation range.
We have newly developed a millimeter-wave vector measurement system for an oscillator-integrated antenna using a time-domain measurement setup. The measurement system consists of two mixers, one for the antenna pattern measurement and one for the phase reference measurement. In this paper, we show the developed W-band millimeter-wave measurement system configuration. In addition, we show the measurement results in the time domain and the estimated magnitude and phase in the frequency domain for a FMCW automotive collision detection radar.
This paper presents a tracking and localization system for passive RFID tags. The localization and tracking system comprise a rotatable RFID reader and sixteen fixed passive tags spread around the room. By strategically positioning passive tags, we demonstrate the possibility of tracking and localizing any passive RFID tag that enters the system. The localization algorithm represents each tag as an x and y coordinate, with the reader representing the origin. The algorithm runs every 0.5 seconds to update all tag locations. The algorithm uses the distance that the passive tag is from the reader and the angle from the positive x-axis the tag lies on to locate the passive RFID tag. The algorithm finds distance using the RSSI (Received Signal Strength Indicator) value and the tag's angle by taking the active tags' average position in that region. This system is helpful for localization and tracking applications. In environments like warehouses or large outdoor areas, where it's crucial to track items or individuals across a vast space.
This paper presents the design, simulation, and experimental validation of a compact full-polarimetric antenna module for short-range radar sensors. Existing radar modules often use same-polarized antennas, potentially missing cross-polarized signals. While polarimetric radar systems offer superior polarization diversity, they are typically costly and complex. Research on radar polarimetry for short-range radar sensors is limited, and a compact antenna design is desirable for seamless integration and flexible placement in modern sensors. Additionally, collecting full-polarimetric data with a small sensor is crucial for developing realistic channel model tailored to short-range sensors. Developing a radar sensor with full-polarimetric operation is challenging due to size limitations and design complexity. This study introduces a 24-GHz full-polarimetric radar system utilizing a novel compact antenna module that captures both co- and cross-polarized signals. The well-designed antenna module, combined with generalized calibration techniques (GCT) demostrated outstanding performance in simulations and experimental validation. Both results closely aligned with ideal target scattering matrices. The proposed module's accuracy and reliability were confirmed through the successful characterization of various targets. These findings highlight the potential of the proposed antenna module for advanced radar sensors applications.
Non-terrestrial networks (NTNs), including satellites, high-altitude platforms (HAPS), and unmanned aerial vehicles (UAVs), operate above the Earth’s surface. Along with ground base stations, they often require the implementation of beamforming and beam tracking techniques to achieve high-speed, low-latency transmission, thereby ensuring seamless coverage. Consequently, diagnosing the functionality of the radio units (RUs) in those network devices and verifying their beamforming patterns are critical for the effective applications of this technology. This paper presents the 3D far-field pattern measurements and calibrations of the RF carrier EIRP levels for millimeter-wave beamforming testing suites that emulate RU operations. This is achieved using a combination of the planar near-field (PNF) and compact antenna test range (CATR) measurement systems at Taiwan Tech. A side-deployed PNF scanner is used in over-the-air (OTA) scan mode for 3D antenna pattern measurement and aperture diagnosis of the RU devices in transmit mode, utilizing controlled scan beams of single-tone and modulated RF carriers. Additionally, a compact range (CR) mode is employed to calibrate the RF EIRP in the peak direction of each RU-scanned beam. Beamforming patterns obtained from the near-field measurements in the OTA scan mode demonstrate good agreements with conventional near-field tests and show reliable EIRP values at 28 GHz for 5G FR2 radio units.
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.
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.
The novel extension of the synthetic aperture radar (SAR) technique to the terahertz (THz) spectrum has emerging short-range applications, especially in an indoor environment. One of the key applications is the generation of a high-resolution indoor environment map in emergency scenarios such as a burning or smoky building, where optical technology might not provide any relevant information. The THz SAR map enables precise localization, classification, and material characterization of concerning objects which can assist in identifying the danger from electrical cables located in the walls and ceilings, and the structural integrity and failure of the walls/ceilings. Hence, the investigation of through-wall sensing at the THz spectrum is of vital importance. This paper addresses the through-wall sensing at the THz spectrum by employing the SAR technique. A miniature version of the wall using gypsum plasterboards is constructed, where the plasterboards are mounted on a frame. Two types of frames are considered, where one frame is of wood and the other is of metal. Additionally, electrical cables are placed between the plasterboards. This miniature version is quite similar to a practical environment. Besides, some of the considered components of the wall are in a burned state. For through-wall sensing, a vector network analyzer (VNA) based testbed is implemented and measurements are recorded in both transmission and reflection modes for three frequency spectrums, which are 75-100 GHz, 220-330 GHz, and 325-500 GHz. At the THz spectrum, the penetration capabilities are always of concern. Therefore, foremost, penetration losses among different components of the wall are investigated with transmission measurements. Further, to evaluate the sensing capabilities behind the wall, transmission measurements are recorded by considering the whole structure of the wall. Besides, relative attenuation among different frequency spectrums is presented. The addressed evaluation is also of significant interest in the area of wireless communication such as 6G and security. Lastly, in reflection mode, a 2D SAR trajectory is implemented and a 3D image of the wall is reconstructed. It is analyzed for identification and precise localization of the cables and frame-blocks. The identified components are further processed for burned state detection.
Spherical Near-Field (SNF) antenna measurements are one of the most accurate antenna characterization methods. However, despite the high accuracy, they have several drawbacks. One of them is the requirement/challenge to acquire not only the amplitude but also the phase of the near-field measurements in order to reconstruct the far-field of the antenna. However, in comparison to amplitude, phase measurements require expensive equipment and are more prone to inaccuracies, particularly at higher frequencies. Moreover, in specific scenarios such as over the air measurements, a reference phase is unavailable or inaccessible. To overcome this, phaseless approaches are of interest and different methods such as using different probes or the two-spheres technique are investigated. The latter has gained more interest in recent research by introducing phase retrieval algorithms such as Wirtinger-Flow, PhaseLift or Gerchberg-Saxton to SNF. We consider an SNF setup with a roll-over-azimuth positioner for the Antenna Under Test (AUT) and a probe mounting with 90° rotation in azimuth. Measuring two spheres with different radii necessitates translating the measurement coordinate system on the AUT-probe axis. This can be done either via an offset of the probe mounting or via a linear axis, whereby the latter is the more flexible solution in terms of measurement automation. In our approach, the considered measurement setup is part of a hybrid test range, consisting of an SNF setup and a Compact Antenna Test Range (CATR). The AUT positioner, part of both CATR and SNF, is mounted on an additional linear axis. Since the linear axis has been designed to measure at different positions in the quiet zone of the CATR, it is not aligned with the near-field probe. Thus, when measuring two spheres, the probe misalignment must be compensated in post-processing by means of an additional rotation of the probe’s spherical mode coefficients. This method allows using arbitrary oriented linear axes to vary the measurement radius and hence increases the flexibility in choosing different radii for the two-sphere technique, which is a critical parameter in the phaseless reconstruction of the far-field.
A custom radar kit that integrates with a portable computer (laptop) for assembly and operation by students and researchers has been developed at MIT Lincoln Laboratory. The assembled radar kit uses two low-cost cylindrical metal cans that serve as the antennas, one for transmitting and one for receiving radar signals. The antennas operate as linearly polarized openended circular waveguides (10.5 cm diameter) fed with a thinwire monopole probe. Over the 2.4 to 2.5 GHz band, the measured reflection coefficient is less than −10 dB, the peak realized gain is greater than 7 dBi, and the half-power beamwidth is approximately 70 degrees in both the E- and Hplanes. FEKO method of moments simulations of the antenna are compared with the measured data and good agreement is demonstrated.
Radar sensors are an essential component in the automotive sector and take over safety-relevant functions in the field of autonomous driving. Therefore, the need for validation of automotive radar systems is increasing. Within this paper, a measurement setup for automated static and dynamic tests of integrated radar sensors is set up in the robot-based measurement chamber available at the Institute of High Frequency Technology, RWTH Aachen University. The system parameters two-way pattern, range and speed resolution as well as angular resolution and separation capability are measured and analyzed for an integrated automotive radar sensor. The measured results show the expected performance of the radar system and point out the high variability of the built setup.
High precision antenna measurements can be carried out in different ways, for example directly in the far-field, in a compact antenna test range (CATR) or in a near-field range. Far-field measurements have the disadvantage that they require a lot of space and are sensitive to environmental influences. Although these effects can be avoided with a CATR, these systems are demanding and expensive. For this reason, simplifying near-field measurement setups are often preferred, whereby three main methods have become established: planar near-field (PNF), cylindrical near-field (CNF) and especially spherical near-field (SNF) measurements. Current measurement setups are usually optimized for one of these techniques and are therefore only of limited use for the other methods. Recent developments have focused on robotic measurement systems, which are able to overcome the boundaries between the different measurement techniques. Due to the high number of degrees of freedom and an almost unlimited positioning and orientation possibility in space, these systems offer numerous advantages due to their flexibility. This allows the same measurement system to be used seamlessly to perform PNF, CNF and SNF measurements. Even for more demanding measurement procedures, for example based on compressed sensing, robotic systems create the possibility to efficiently approach the required sampling points. At the Institute of High Frequency Technology at RWTH Aachen University, such a robot-based measurement setup is currently being established. In addition to the six-axis robot arm, the system has two additional axes, specifically a linear axis on whose slide a rotary axis is mounted. In the currently used configuration, the antenna under test is mounted on the axis of rotation, while the probe antenna is installed at the robotic arm. This results in a total of eight degrees of freedom combined in a novel test range design, which distinguishes the measurement setup from existing ones. Further details on the measurement setup, the implementation of antenna and radar measurements and the operation of the entire system will be explained.