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Spherical Near-Field antenna measurements are broadly used for vehicular measurements, which almost always include several antennas. Due to the large size of vehicles and the reduced size of near-field ranges, it is often impossible to displace the vehicle so that the desired Antenna Under Test (AUT) be in the center of the measurement sphere - and when it is possible, it is highly impractical to repeatably displace the vehicle for each of the antennas. Nevertheless, it is often required to retrieve the radiation characteristics of the AUT as if it were centered. In this work, Parallax-based methods for the correction of near-field acquired data are discussed, and a novel method based on the correction of the probe’s relative view angle and distance to the offset AUT is introduced. This method, additionally, does not require any matrix (pseudo)inversion for the calculation of the Spherical Wave Coefficients (SWCs) and can be solved with classical FFT-based Near-Field-to-Far-Field Transformations (NFFFT) based on the Wacker transmission formula.
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.
Transceiver satellites with a ”bent-pipe” payload are commonly used in communication systems. Accuracy of measurement of their main End-to-End (E2E) parameters, such as Saturating Flux Density (SFD), Gain flatness (G/F), Equivalent Isotropic Radiated Power (EIRP) and Gain over Temperature (G/T) depends not only on the test setup, but also on the accessibility of different test points in the payload. In this work, we focus on the error budget for different accessibility levels when the payload is tested in Planar Near-Field (PNF).
As the demand for efficient and accurate characterization of mmWave antennas grows, compact antenna test ranges (CATRs) have become preferred alternatives to traditional far-field ranges due to their smaller size requirements. CATRs transform spherical waves into planar waves at short distances using a parabolic reflector. The quality of the CATR’s quiet zone depends on minimizing edge diffractions caused by fields reflecting off the reflector’s rim. Techniques like serrated and blended rolled edges are used to reduce these diffractions. While blended edges perform better, serrated edges are more commonly used due to their ease of manufacturing and lower cost. To enhance the convenience, affordability, and performance of CATRs, this work introduces a 3D-printed blended edge reflector for a Ka-band system. Manufactured on a desktop 3D printer, this high-performing reflector shows promising results. Additionally, a surface roughness analysis of CATR reflectors quantifies the impact of surface roughness on the purity of plane waves in the quiet zone across various frequencies. Measurement results from the additive manufactured reflector align with TICRA GRASP simulations. This work aims to improve efficiency and accuracy in mmWave and sub-terahertz frequency measurements, which require high precision in antenna characterization.
The extrapolation method is widely used for antenna absolute far field gain calibration. The technique involves measuring responses between precisely aligned antenna pairs across varying distances. Previous studies have suggested that how one measures the separation distance—whether from aperture face to face or from phase center to phase center—doesn't influence the resulting far-field gain. However, our present study demonstrates that this assumption is incorrect. The choice of reference points for measuring separation distance can indeed impact the computed far-field gains. Our investigation shows that using the distance from the phase centers provides the most accurate far-field gain. Through numerical experiments and measurement data, we illustrate the discrepancies in the far-field gains caused by different distance definitions. Since the phase center of the antenna under test is usually unknown in practice, finding the phase center separation distances to apply to the extrapolation calculation isn't straightforward. To address this, we introduce a novel searching algorithm that varies an offset distance during polynomial fitting. This generates various convergence curves with different trends and rates, allowing for the accurate determination of phase center separation distances. The proposed algorithm not only enhances the accuracy of the antenna gain extrapolation method but also provides the phase center information of the antenna under test, all without requiring additional measurements.
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.
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.
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.
This paper presents an analysis of the truncation errors of co-pol and cross-pol data by comparing a far-field pattern obtained from simulation, with different patterns obtained from the near-field to far-field transformation for different scan area sizes. It is shown how these errors are reduced when the scan area is larger, the reason being that more significant fields are being captured by the probe; however, the improvement comes at the expense of longer measurement time. From this problem, a new method is proposed where the system makes sure to measure all the significant fields and avoid the insignificant ones, reducing the measurement time and increasing the accuracy.
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.
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.
The feasibility and radiation properties of the nullifier-based monopole array antenna are studied and analyzed. Since this antenna does not require grounding, arrays of this antenna are less prone to mutual coupling, at least to the part stemming from mixing currents in a common ground plane. Simulations results for the performance of a 2-element array of the nullifier-based monopole antenna and the mutual coupling between the elements are presented and compared with those of a similar array of conventional monopole. The proposed array of nullifier-based monopole can be used in wireless communication systems such as RADAR and IoT applications.
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.
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.
This paper presents antenna design and measurements for wireless audio applications in the 470-600 MHz frequency range. Simulation and measurement results show that going from an external whip antenna to an internal helix antenna, realized gain was reduced between 2-4 dB across the desired frequency band, agreeing with or better than theoretical maximum gain calculations.
A free-space material measurement for a small dielectric plate using a truncated Gaussian beam whose beam width is smaller than the material under test (MUT) is described. Measurement results of two glass plates of different thicknesses at W-band (75-110 GHz) show its validity and the minimum beam width of the truncated Gaussian beam for the reliable material property measurement of a small planar MUT.
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.
Frequency band requirements for satcom applications in certain cases overlap two conventional microwave frequency bands. Characterizing antennas using near field techniques over such bands require two separate probes resulting in substantial increase in measurement time. This work is motivated by providing solution to such requirements of overlapping bands (K and Ka-band) and wideband operation over an octave frequency from 17-33 GHz. We propose a new WR-38 band and present the design and development of WR-38 waveguide probe realized using 3D metal printing. Impact of higher order modes on operational bandwidth of waveguide, 3D metal printing surface roughness and fabrication tolerances is investigated. Fabricated probe is characterized using planar near field (PNF) and measured results are presented. Performance comparison is done by characterizing SGH-1800 (18-26.5 GHz) and SGH-2200 (22-33 GHz) with 3D printed WR-38 probe and commercial WR-42 and WR-34 probes.