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Anechoic ranges require constant temperature and humidity, proper lighting to be able to work inside the range and closed-circuit television (CCTV) cameras to monitor the system while the measurement is being done. In addition, anechoic chambers require fire detection and suppression. Traditionally these penetrations are minimized and placed in non-critical areas. But the true effect of them has not been fully investigated. In this paper, antenna measurements as simulated in an indoor far field range. The approach to model the measurement is like the one the author presented in [1] and [2]. Thus, a range antenna (or near- field probe) and an antenna under test (AUT) are placed in free space and the AUT is rotated at discrete angles as it was done in [1]. Then a second model includes CCTV cameras, HVAC vents, light fixtures and both air sampling tubes and fire suppression nozzles and placed around. The simulation with these disruptions is repeated at the given discrete angles. The model does not include the absorber on the range. The model assumes a perfect absorber and the results of the simulated antenna measurement are compared to an ideal case with no disruptions. The results, while being approximations, provide a worst-case error for those disruptions of the RF-absorber layout. The results can be used to estimate the potential uncertainty on the measurement caused by the different systems that must be part of the anechoic enclosure. The technique is applied here to indoor far field measurements, and for near-field systems. Results show that for your typical roll over azimuth positioner, the effects of the penetrations on the ceiling are very small with differences in the -35 to -40 dB levels.
A new method is developed for accurate transmission measurements through a surface using a far-field Gaussian weighting approach for use in anechoic chambers. A trivial approach to measuring transmission characteristics would be to mount a sample-under-test between two antennas and simply measure the boresight transmission using a network analyzer. This approach is enhanced by instead measuring the transmitted fields over a hemispherical field-of-view and then weighting the measured far-fields to synthesize a Gaussian illumination of the sample. This approach can be utilized to effectively illuminate the sample-under-test with an arbitrary excitation with a high degree of customization in post-processing (e.g., beam polarization, direction, waist size, and location). The approach is validated by characterizing transmission through a copper clad substrate and a frequency selective surface (FSS) from 4 to 40 GHz. Additionally, a sample of Rogers 5870 is measured from 8 to 40 GHz. For each sample-under-test, S21 measurements are compared for the boresight and Gaussian weighted methods, showing greater agreement with theoretical or simulated values for the Gaussian case.
This paper presents a novel approach to radome measurement. Traditional radome measurements in anechoic chambers provide information on radome losses and beam deflection but cannot fully capture the RF environment the system will be operating in once deployed, which includes scattering sources and diffraction from the radome. It is also very difficult to characterize radome effects using similar approaches once the radome has been installed. This research investigates the use of a USRP-based field probing system to characterize the RF field of view for a radome located at the OneRY Range at Wright-Patterson Air Force Base (WPAFB) in Dayton, Ohio. Using a custom-built planar positioner along with two channels of the USRP, relative amplitude and phase measurements are taken inside the radome and processed into angle and time of arrival data, which are presented as angle vs distance plots. These show the direction and distance of scattering sources in the field of view of the aperture. For this radome, two scattering sources are identified along the path from the installation to a secondary transmit site. Diffraction from the radome wall is also detected and characterized. This method represents a new way of visualizing scattering and diffraction in radome-based installations. This method also provides a way to characterize existing radome installations that have not been measured in anechoic chambers, or in situations where the RF hardware has been changed to cover frequencies not previously characterized. The processing algorithm is presented along with plots comparing indoor and radome collects. Results from a 2D electromagnetics simulation are also presented to further validate diffraction measurements.
The wall-reflectivity technique is a proven method to validate the reflectivity reduction of large metallic walls covered with electromagnetic absorbing materials. While for a theoretical perspective it is sufficient to perform only two quasi-monostatic measurements, one for a known reference target and one of the wall, it has been shown that system dynamic range as well as clutter reduction can be achieved by performing spatial averaging using a linear slide, taking several measurements along the perpendicular direction against the wall. In this work the effect of improvements of the accuracy and positioning repeatability of the linear track is investigated. Measurement results are shown indicating the improved capabilities of the measurement setup.
Near-Field (NF) antenna measurement ranges have evolved as an alternative to Far-Field (FF) ranges to be the prominent method for pattern estimation from measurement. This is because NF ranges are more convenient to use and require much less space in laboratories [1]. The Microwave Vision Group (MVG) StarGate series, such as the legacy Satimo StarGate 64 (SG64), employs an array of multiplexed probes to perform measurements, sampling across a synthetic aperture created by moving the test antenna with respect to the probe array. This example of a commercial system does not use a Vector Network Analyzer (VNA), and was not designed to be updated. This means that it cannot benefit from improvements made in RF measurement equipment, requiring instead that a new system be purchased, which is unrealistic for many users. This work describes the initial process of updating a legacy SG64 to use a VNA. It includes characterization of the control signals, the transmit and receive paths, as well as the potential improvements to performance and lifetime that upgrading the legacy system to a VNA-based configuration offers.
The primary role of an anechoic chamber is to provide a reflection free environment that can be used for electro-magnetic measurements, with antenna pattern being one of the most prominent measurements utilizing anechoic chambers. Real world anechoic chambers, however, rarely provide a reflection free environment. Reflections in an anechoic chamber can arise from a mismatch between the absorber size and the frequency used, the angle of incidence between the absorbers and the wave front, various metallic objects inside the chamber and more. As reflections can introduce impairments in the measurements, it is highly desirable to measure an anechoic chamber for reflections and reduce these reflections as much as possible (especially in the designated “quiet zone”). This paper introduces an innovative reflection evaluation method that harnesses both communication processing and radar processing to localize reflection sources in an anechoic chamber. The chamber setup consists of a probe and an antenna under test (AUT). The probe emits a signal, which is directly received by the AUT along with reflections within the anechoic chamber. Employing either a frequency modulated continuous-wave (FMCW) or stepped-frequency signal, the indirect path length is estimated, resulting in a ellipsoid representing potential reflection points. By intersecting multiple ellipsoids generated through relocating the probe and projecting the intersection onto the chamber, the reflection location is determined. The method’s efficiency has been demonstrated through implementation and validation in an anechoic chamber, with the paper presenting real measurement results for validation purposes.
Radiated Two Stage (RTS) over-the-air wireless testing method is a well known method for evaluating the performance of wireless devices, over multiple radio access technologies. At the heart of this method, all impairments are generated mathematically and loaded into a channel emulator such that the testing is done in a controllable and repeatable manner. After the desired signal passes through the channel emulator, it is transmitted over-the-air to the device under test. This final leg of the over-the-air transmission introduces an additional channel section that is often undesired. To remove the effect of the transmission over-the-air, a precoding of the transmitted signal is performed, often based on the reporting of the power received by the device under test at each of its antenna ports. However, when large metal objects are tested, significant multi-path can occur and thus creating frequency-selective channels that are not easily captured by power measurements. In this paper this phenomenon is analyzed from a mathematical perspective, a simulation example is shown with the effect of power averaging over different bandwidths. We demonstrate that reducing the signal bandwidth used for power measurements significantly improves the accuracy of the precoding matrices of the signal, thus more effectively eliminating the undesired last leg.
Accurate determination of the far-field distance is essential for characterizing antenna performance. The Fraunhofer distance is widely used to estimate the far-field distance of antennas; however, the true far-field distance is often quite different from the Fraunhofer distance depending on antenna type and size. This study presents a comprehensive simulation framework to investigate the far-field distance of dielectric lens antennas operating in the sub-THz band. Using the HFSS SBR+ solver, the framework replicates a direct antenna measurement setup, enabling efficient and accurate analysis of electrically large problems. The far-field distance is defined based on gain saturation, and a new formula is derived through extensive parametric simulations, accounting for lens diameters and operating frequencies. Experimental validation is conducted using a modular anechoic chamber, demonstrating strong agreement between measured and simulated results. The findings confirm the reliability of the proposed framework and the derived formula, offering a practical tool for designing compact antenna test setups. This work advances the understanding of far-field criteria for lens antennas and provides a foundation for future research in antenna measurement systems.
Modern wireless standards such as LTE, HSPA, WiMAX, and 5G have introduced the need for more sophisticated testing of devices that use multi-antenna systems. Traditional Over-the-Air (OTA) test methods, initially developed for single-input single-output (SISO) devices, fall short when evaluating complex systems like Multiple-Input Multiple-Output (MIMO) devices. This paper discusses the convergence of traditional testing methodologies based on conducted RF testing and OTA antenna system test methodologies toward testing of the full antenna equipped device. This convergence embraces two important testing needs and scenarios: replay of preconfigured scenario, based on spatial fading emulation (SFE) / channel modelling and dynamic hardware-in-the-loop testing, where changes in the hardware state in reflected in the status of the testing scenario. By the integration of channel emulation and multiprobe anechoic configurations, scalable and flexible test strategies can be achieved accommodating testing needs in personal and automotive communication systems but also defense applications.
The Free Space Voltage Standing Wave Ratio (FSVSWR) method has been the de facto standard for assessing anechoic chamber performance for more than fifty years. However, it depends on specialized linear scanning hardware and can take several days to complete a full data sweep. In this paper, a circular scan approach is introduced where the receive antenna is mounted at the quiet-zone boundary on a standard turntable or multi-axis positioner and then rotated through 360° to obtain a single-cut radiation pattern. We apply three data-processing techniques, namely plane wave decomposition, matched filtering and matched filtering with spectral filter, to extract the chamber’s plane wave spectrum and to locate reflections. To ensure accurate energy recovery for each reflection, we incorporate an anti-leakage compensation step into the spectrally filtered matched filtering process. The proposed methods are validated through numerical simulations and measurements in a fully anechoic chamber.
One of the major challenges of radio frequency (RF) propagation at 60 GHz is the high path loss and significant attenuation due to obstructions. These limitations hinder the implementation of wireless communication when the line-of-sight (LOS) path between the transmitter and receiver is blocked. To address this, intentional use of reflective environments is proposed as a potential solution to establish alternative paths between the transmitter and receiver particularly for Industrial Internet of Things (IIoT) applications. We have developed a test chamber to create and alter reflective scenarios at 60 GHz with full traceability to primary standards. The chamber allows device testing and scenario design for wireless devices at 60 GHz. Measurements were conducted in a hybrid anechoic/reflective chamber using open-ended waveguide antennas for transmission and reception. A synthetic aperture at the receiver was employed to emulate large array configurations, by moving a receiver antenna with a small articulated robot to create up to a 35×35-element grid. Spherical reflectors of various sizes and positions were tested to generate intentional reflections. The channel-induced error vector magnitude (EVM) using 64-QAM modulation was measured for each configuration and for different array sizes. Results show that EVM improves with increasing reflector size. The study also identifies the minimum array sizes needed to achieve acceptable EVM performance. These findings are promising for the development of reliable 60 GHz WLAN systems using reflector-assisted non-line-of-sight (NLOS) communication.
Tapered anechoic ranges were introduced in the late 1960s. Since their introduction tapered anechoic chambers have become popular tools for the measurement of antenna patterns at frequencies under 1 GHz. Dating back to their first installations, several papers mention the fact that these chambers did not have a spherical wave propagation and thus, the Friis transmission equation to measure gain cannot be applied [1,2]. The array factor theory of taper chambers presented in [3] states that from the point of view of the antenna in the QZ the tapered chamber appears to be a free space environment. The phase behavior across the QZ, reported in [4] appears to agree with the theory since the phase distribution follows the far field equation. In this paper simulations for a dipole and a biconical antenna are performed that suggest that the array factor theory for the tapered ranges while not perfect provides an approximated explanation for their operation. The simulations confirm the measurements done in [2] and additionally show that at some discrete frequencies the propagation in the tapered range does follow closely the free space attenuation.
With the increasing need for higher quality automotive connectivity and location services, full-vehicle over- the-air testing has become a topic of growing interest. As the size and costs of ranges required for such tests is however prohibitive, many companies have looked into combining antenna measurement and electromagnetic compatibility tests into the same chamber environment. This paper provides an overview analysis of the complexity and constraints associated with such a choice. A numerical investigation of an entire test range is offered to derive conclusions on possible site limitations relating to unwanted reflections within a dual-purpose chamber.
This paper provides a brief overview of two new concepts of plane wave generators (PWGs) for applications in antenna and wireless device measurements. These PWGs aim to increase flexibility in emulating various multipath testing conditions within the same measurement environment, addressing the high cost and complexity of conventional systems. The first concept, utilizing a chamber antenna array (CAA) inside an overmoded waveguide (WG), leverages the reflecting walls of the metal rectangular WG in conjunction with a CAA to synthesize obliquely incident plane-wave fields at the device under test. This has been demonstrated for telecom sub-6 GHz applications (e.g., for total radiated power and pattern measurements), with ongoing studies on its evolution to Reconfigurable Intelligent Surface (RIS) based PWGs for millimeter-wave frequencies. We discuss the design and analysis foundations, highlighting key requirements and limitations to maximize flexibility. We use simulations with a customized modeling framework and measurements from our first prototype systems: an overloaded waveguide (WG) chamber with a 6 × 7 CAA at 915 MHz and a 16 × 16 RIS PWG at 28 GHz. WG-based PWG is evaluated using metrics such as uniformity, angular spread, and bandwidth. For the RIS PWG prototype, we demonstrate the practically achievable complex reflection coefficient values to evaluate the requirements for PWG applications.
Absorber treatment for an anechoic range is designed to attenuate the potential reflections from the walls, ceiling, and floor and to keep a certain level below the direct path between the range antenna (or probe) and the quiet zone (or minimum radiated sphere for spherical near-field ranges). There are, however, some antenna measurement systems where the range changes or moves as the data is acquired. In some cases, the probe moves around the antenna-under-test (AUT) along a section of circle supported by an arch or a gantry. In other ranges, the multiple probes are switched on and off; these probes are supported by an arch. Because the direction of the range moves with respect to the walls, ceiling, and floor, it is a bit more complex to arrive to an optimal absorber layout, as well as locating the preferred placements for the instrument rack, door, and vents in the range. In this paper, a higher-order-basis-function method of moments approach is used to model a gantry-supported probe as it moves around the location of the AUT. The power density at the walls as the probe moves is analyzed to arrive to an optimal absorber layout that will provide adequate levels of reflections for measuring an antenna. The paper looks at a gantry that moves from +135° to -135° with the AUT rotating 180° and for a gantry that moves from 0° to +135° with the AUT rotating 360°. The latter will require a smaller range with one of the walls closer to the location of the antenna under test. A series of recommendations based on the electrical size of the absorber at different areas of the range are provided.
Piezoelectric transmitters operating at acoustical resonance have been shown to radiate effectively in the Very Low Frequency (3 kHz to 30 kHz) and Low Frequency (30 kHz to 300 kHz) regimes. Such transmitters make use of the inverse piezoelectric effect to couple electrical signals into mechanical vibrations, resulting in near field radiation. This new class of electrically small antennas, known as mechanical antennas or ‘mechtennas’ can provide several orders of magnitude higher efficiency than similarly sized electrically small conventional dipoles. Measuring the dipole-like near field pattern of such piezoelectric field emitters in the Very Low Frequency and Low Frequency range using conventional techniques is not possible. To address this limitation, a simple capacitor plate-based setup is presented that enables the measurement and plotting of the near field patterns of such transmitters. Design and simulation of the capacitor plates to model the fields along with electric field pattern measurements of a Y 36◦ cut Lithium Niobate transmitter having longitudinal mode resonance at 82 kHz are presented.
Mode filtering has been shown to be very effective in suppressing spurious reflections in antenna measurements. Specifically, it has been well documented that in the quasi-far-field, the two polarizations are decoupled, making it possible to apply standard cylindrical near-field theory on the amplitude and phase data acquired from a single polarization measurement on a great circle cut [1]. The method was further extended to allow data collected from an unequally spaced angular abscissa by formulating the solution as a pseudo-inversion of the Fourier matrix [2]. This formulation, however, can be prone to spectral leakage because of nonorthogonality of the Fourier basis on an irregularly sampled grid, especially when the positions deviate significantly from the regular grid [2]. In this paper, we propose to use Compressed Sensing (CS) to compute the Cylindrical Mode Coefficients (CMCs), which improves the signal to noise ratio, allowing more accurate recovery of the prominent modes. The CS recovery is tenable because with the coordinate translation of the measurement pattern to the rotation center, the Maximum Radial Extent (MRE) of the antenna under test is greatly reduced, making CMCs quite sparse in the mode domain. The novel application of CS presented in this paper further expands the generality of the mode filtering method, which is now applicable to under-sampled data (at below the Nyquist rate) acquired on positions that grossly deviate from the equally-spaced regular grid.
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.
We describe a planar near-field instrument capable of measuring the non-linear response of an electronically steered antenna (ESA) up to the third harmonic while requiring only a single scan with a single probe. The system performs phase-coherent measurements of the aperture near-field at the fundamental frequency, second harmonic, and third harmonic simultaneously, which are then transformed to the far-field. When system losses are appropriately accounted for, these far-fields are accurate representations of the harmonic patterns relative to the fundamental. A broadband dual-polarized probe combined with a specially-configured network analyzer is used to capture all frequencies and both polarizations within a single scan. Using a ultra-broadband probe introduces some limitations to the measurement, but offers a significant increase in measurement speed. In this paper we disclose various architecture and design aspects of the instrument, discuss its advantages and limitations, and compare non-linear PNF measurements with non-linear array simulations and direct far-field measurements.
The purpose of radar cross-section (RCS) measurement is to determine the amount of scattering that occurs when the radar signal illuminates the target. It is generally performed to prove a design concept. RCS measurement chamber requires a good signal-to-noise ratio during the measurement. When the measurement is performed in a non-controlled environment, coherent background subtraction associated with time gating is commonly used to improve the quality of the RCS data. Although these techniques are usually effective, residual clutter and background level still need to be removed to accurately characterize the target’s RCS in highly cluttered environments, such as semi-anechoic chambers. In this paper, a four-step post-processing technique is presented. In addition to the vector background subtraction and timegating techniques implemented in our previous work, a statistical algorithm called Principal Component Analysis (PCA) is applied to the ISAR image of the target. It is an extension of the PCA technique to RCS measurement. It is shown that residual background and clutter can be reduced by the statistical filtering method through eigenvalue decomposition of the RCS data. The technique is presented and evaluated through measurement of the RCS of a dihedral corner reflector at the X-band in the semi-anechoic chamber of the Directed Energy Research Center.