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In an antenna production environment, efficient utilization of test chamber facilities is paramount to maintaining schedule and budget compliance. In many cases, troubleshooting and evaluation efforts must be offloaded to secondary test facilities to avoid the costly impact of sustained range downtime. Unfortunately, these facilities may be more limited in their capabilities and thus less conducive to efficient product evaluation. This paper presents a detailed recap of a recent investigation which relied on non-standard evaluation techniques. A modern AESA enhanced with experimental beam steer capabilities triggered excessive radome heating that resulted in considerable damage to the composite material and substantial delays in the contract’s delivery schedule. As a conventional high- power range was unavailable to perform the investigation, an unorthodox approach to the troubleshooting and evaluation effort was required. Particular technical emphasis will be placed on this investigation’s reliance on thermal measurement equipment as a substitute for conventional RF measurement methods. Implementation of the evaluation in a non-standard test environment will also be highlighted as a practical application for engineers operating in a similar manufacturing setting where non-standard technical solutions are often necessitated. Associated challenges, limitations, and insights will be emphasized.
This paper presents a numerical investigation into the cylindrical mode filtering method and the application of the Compressed Sensing (CS) for far-field single-cut antenna pattern measurements. For measuring a single cut antenna pattern in a far- or quasi-far-field distance, cylindrical mode filtering using an intentional offset effectively removes multipath reflections from the test environment. The CS algorithm enhances this method by enabling sampling on an irregularly spaced grid. This investigation uses numerically simulated data to examine the cylindrical mode filtering method, addressing questions about the mechanism of modal separation and sparsification facilitated by the coordinate translation of the pattern to the rotation center. It also discusses potential limitations of the method, including aspects not previously covered in the literature. We then assess the efficacy of modal recovery via CS compared to FFT and pseudo-inverse methods for both non-sparse and sparse modal data. For non- sparse data, the L1 minimization used by CS can accurately compute the antenna modes but does not offer advantages in terms of reducing the number of samples needed. When the modal data is sparse, the CS algorithm not only allows for irregular sampling but also reduces the number of samples below the Nyquist rate. Additionally, the study evaluates the algorithm’s robustness against added noise and compares its performance with traditional dense data acquisition schemes. The findings provide greater insights into the cylindrical mode filtering method and validate the effectiveness of the CS algorithm.
The size and optics of a Compact Antenna Test Range (CATR) determine its quiet zone and the lowest frequency at which it will meet nominal quiet zone specifications. If a reflector is not large enough to present a sufficient multi-wavelength surface at a given frequency, a plane wave is not generated. Operating compact ranges at lower and lower frequencies is a continuing desire in the measurement community. The normal solution for both instances is to increase the reflector size. This leads to larger test chambers, hence increasing cost. Collecting spherical near- field (SNF) data in a CATR within its normal operating frequency band is well known. However, this leads to collecting more data than required to obtain principal plane cuts in the CATR. This paper presents a study and empirical data on using low-frequency range antennas that operate down to one half the nominal CATR low frequency using SNF techniques to measure test articles at these frequencies with relative accuracy. The paper includes simulations of the quiet zone performance at low frequencies.
This is a continuation of the work presented at the AMTA 2022 symposium to assess the accuracy of on-axis antenna gain with commercially available computational electromagnetic (CEM) solvers [1]. Common practice for computing antenna gain normalization via the gain-transfer technique is to use the on-axis NRL gain curve of a pyramidal standard gain horn (SGH) derived by Schelkunoff and Slayton [2], [3]. Due to approximations in this formulation, Slayton assessed an uncertainty of ±0.3 dB for typical SGHs operating above 2.6 GHz. Since this uncertainty term is often one of the largest terms in the range measurement uncertainty budget for AUT gain, it is highly desirable to reduce it. Many studies in the past have attempted to improve upon Slayton’s expressions for SGH gain, but none have achieved widespread use. The previous investigation demonstrated the use of several commercially available solvers, including HFSSTM, CST Studio Suite®, and FEKO® to model the on-axis directivity and gain of a commercial off-the-shelf (COTS) X-band SGH [1]. In that work, the CEM simulation results from multiple solvers in HFSSTM, CST Studio Suite®, and FEKO® are shown to be within ±0.0075 dB of each other. This work is an extension to study how closely the simulation models match recent measurements of gain for the same MVG SGH820 horn discussed in previous paper. These measured and modeled results are compared with the international intercomparison results of a similar SGH [4], in conjunction with a best-estimated simulation model of the original dimensions from [4]. To capture the differences of the physical as-built antenna versus the simulation model, a simple tolerance study in simulation is performed based on the build tolerances of the antenna to provide an uncertainty estimate of the simulation results.
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.
For many applications, one needs to know the accurate in-situ response of complex antennas mounted on complex platforms. To accomplish this objective, modern numerical EM simulation software apply the equivalence theorem and Huygens' principle to construct equivalent electrical and magnetic sources within an arbitrarily chosen antenna volume from measured antenna data on a finite ground plane. These sources are then used to perform on-platform simulations to estimate in-situ antenna performance. However, these measured far-field data are often contaminated by additional scattering from the ground plane. This paper studies the application and effectiveness of a processing method for removing such contaminations directly from the far- filed data by employing spherical wave modes filtering. A simple patch antenna and an array of patch antennas tuned to 1.575 GHz are used for this study. A full-size simplified C-12J Huron aircraft model is used as the target platform. The performance of the proposed method is compared against the reference gain pattern data obtained from directly solving the method of moments (MoM) integral equations (HFSS-IE) with antennas mounted on the target platform.
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.
The objective of this paper is to provide some guidelines about the measurement uncertainty of Spherical Near Field (SNF) ranges when they are used to derive near field figure of merits instead of more conventional far field-based metrics. One of the main advantages of the SNF ranges is their flexibility. Indeed, from the NF scanning, the spherical wave expansion is applied, and it can be used as a powerful, accurate and efficient propagation tool, able to evaluate figures of merits at (almost) any distance from the device under test. This feature is particularly useful in the testing of modern antenna systems intended to operate in specific regions of space instead of conventional far field scenarios. Examples are Plane Wave Generators (PWG) which create a uniform field distribution in the proximity of the device, or more generic field synthesizer devices. Despite the flexibility of SNF systems, the evaluation of their uncertainty budgets is normally limited to far field-based metrics. Understanding under which conditions and in which measurement scenarios such uncertainty budgets are applicable to more generic near field metrics is the main topic addressed in this paper.
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.
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.
Classic methods for extracting material characteristics typically demand rigorous calibration, multiple samples, precise location measurements, etc. A recent research effort led by Zhao Caijun, Jiang Quanxing, and Jing Shenhui utilized a simple transmission/reflection method to extract high accuracy permittivity results from a Coaxial Line system. This method uses two uncalibrated scattering parameter measurements: one of the empty fixture and one of the sample at a single position. This paper extends the method to produce accurate permittivity results from a Rectangular Waveguide system once corrected for detector mismatch.
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.