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Far Field

Compact Bistatic Radar Cross Section Measurement System Using a New Plane-Wave Synthesis
Masanobu Hirose, Satoru Kurokawa, October 2023

We propose a compact bistatic radar cross section (RCS) measurement system using a new 2D plane-wave synthesis (PWS) employing 2D propagating plane-wave expansion and a single-cut near-field far-field transformation (SCNFFFT). Our system has been successfully applied to the bistatic RCS measurements of a metasurface (100 mm width, 50 mm height, and 0.127 mm thickness) at 60 GHz where two horn antennas are used for the PWS (Tx) and the SCNFFFT (Rx) and placed at the circular distances of 1.735 m and 0.35 m respectively. The peak and pattern errors of the RCS are 0.4 dB and below -25 dB respectively. Using the proposed 2D PWS and SCNFFFT, the compact 2D bistatic RCS measurement system is realized without large equipment such as CATR.

On the limitations of off-normal-incident measurement of reflectivity performance of microwave absorbers
Amin Enayati, Vince Rodriguez, October 2023

Challenges and limitations of off-normal reflectivity measurements of microwave anechoic chambers are presented. The NRL-Arch technique has been investigated for measurement of WAVASORB® VHP-26 for extreme incident angles; e. g. 80° for the frequency range of 1-20 GHz. It has been shown that the standard test techniques such as NRL-Arch have limitations and for extreme incident angles, simulation values are more reliable in most of the cases. In some rare cases some advanced techniques are available in the literature which are expensive and can be recommended for special projects only

Experimental Validation of Linear Multiprobe Arrays for Fast and Accurate PNF Antenna Characterizations
Francesco Saccardi, Andrea Giacomini, Lars Foged, Nicolas Gross, Thierry Blin, Per Iversen, Kim Hassett, Roni Braun, Lior Shmidov, Meng He, Chen Chen, Xavier Bland, October 2023

The application of multi-probe (MP) technology in near-field (NF) measurement scenarios is well-known for its ability to significantly reduce test time. This is achieved by electronically sampling the radiated field using different probes in the array, eliminating the need for mechanical probe movement. However, in planar near-field (PNF) measurements, the accuracy is contingent on probe correction (PC) during post-processing. Characterizing the pattern of each individual sensor in a PNF MP system presents an additional challenge, often being impractical or impossible. Previous publications have explored various approaches to address this challenge and achieve an accurate characterization of the MP equivalent pattern. In this paper, we focus on the average probe pattern (APP) technique, which involves the experimental determination of the MP pattern. To validate the effectiveness of the APP technique, we conducted experiments on a large PNF MP system equipped with a 4.65m probe array. Our measurements focused on an electrically large 1.5m diameter reflector antenna (MVG SR150 reflector, fed by a quad-ridge horn) operating in the 1.8–6.0 GHz frequency range. The validation process involved the comparison of MP measurements processed with the APP technique and conventional open-ended waveguide (OEW) PNF measurements. To ensure the reliability of the validation, we conducted the comparative tests within the same frequency range and test setup. This minimized the impact of measurement errors, enabling a robust and accurate comparison between the techniques. By validating the APP technique's effectiveness, we aim to establish its suitability for improving accuracy in PNF MP system measurements.

Accurate Antenna Characterisation at UHF/VHF Frequencies with Plane Wave Generator Systems
Lars Foged, Francesco Saccardi, Vincenzo Schirosi, Andrea Giacomini, Francesco Scattone, Lucia Scialacqua, Arianna Diamanti, Enrico Tartaglino, Nicolas Gross, Shoaib Anwar, Evgueni Kaverine, Per Iversen, Edward Szpindor, October 2023

This paper aims to compare the capabilities and advantages of Plane Wave Generators (PWG) and Compact Antenna Test Ranges (CATR) of similar physical size, operating in the VHF/UHF frequency range. The primary focus of this study is on the benefits of utilizing the PWG at such low frequencies for antenna and device characterization. We demonstrate that the PWG offers a superior approximation to the far-field (FF) plane wave condition in the quiet zone (QZ) compared to similar sized CATR systems. The better performance of the PWG at these frequencies is expected, as this is an unusual frequency range for an optical system such as CATR. Due to the efficient focusing properties of the array, the PWG exhibits significantly reduced side wall illumination and thus resulting reflections within the anechoic chamber. This translates into a substantial improvement in overall measurement uncertainty. The CATR system requires specific edge treatment, such as serrations or rolled edges, which increase the overall system's size and associated cost while reducing the effective area of the reflector. Our findings suggest that at low frequencies such as VHF/UHF, a PWG-based solution can be designed to comparable performance to the CATR system while maintaining a considerably smaller size and lower cost, making it an attractive alternative for low frequency antenna testing at in anechoic environments.

Estimating Uncertainties of System Level RF Parameters of Transponder Spacecraft Payloads
Edwin Barry, Pieter Betjes, Patrick Pelland, Daniël Janse van Rensburg, October 2023

This paper provides an overview of measurement uncertainties associated with a planar near-field test methodology for measuring typical system level characteristics of transceiver payloads. We describe a framework for analyzing the uncertainties when measuring these system level RF parameters in a near-field range. More specifically, saturating flux density (SFD), equivalent isotropic radiated power (EIRP), gain-to-noise temperature (G/T) and end-to-end gain vs. frequency are addressed. Results from a set of validation measurements, performed on a frequency converting simulated payload are used as baseline. A combination of analysis and direct measurements are presented to validate the measurement methodology for each parameter and estimate corresponding uncertainties. The contribution of this paper is the presentation of these methodologies and establishing an initial set of uncertainty boundaries to qualify the near-field test approach for this purpose.

A Simple Algebraic Approach for Finding Minimal but Most Representative Measurement Points of Antenna Patterns
Robert Geise, October 2023

In this contribution a simple algebraic approach is discussed on the minimum of required sample points for either a nearfield or a farfield configuration to calculate the antenna’s current distributions to accurately reconstruct the antenna’s radiation pattern anywhere in space. The proposed algebraic approach comprises a Gaussian quadrature sampling scheme for a set of Hertzian dipoles with unkown amplitudes representing the antenna current distribution. The algebraic equation system with the number of unknown amplitudes then suggests the minimum of required sample points in the radiated field. In this initial study simulation examples of a dipole antenna and a horn antenna are presented validating the proposed algorithm.

Horn Antenna Manufacturing Using Additive Manufacturing Techniques
Jeffrey Fordham, Jon Swarner, Eric Kim, Griffin Fox, Corey Agan, October 2023

Additive manufacturing methods, also known as 3D printing, have proven to offer many advantages in manufacturing a wide range of products. These methods have advantages of rapid prototyping, rapid production, and the ability to produce mechanical parts that cannot be realized with traditional machining or casting methods. Various methods have been developed which use a wide variety of raw materials and methods. For example, the Selective Laser Sintering (SLS) method has been used in 3D printing of antennas [1], where metal conductivity is required along with accurate mechanical tolerancing. Other methods using plastic such as stereolithography (SLA) where a liquid photopolymer resin is cured using an ultraviolet laser and Fused Deposit Modeling (FDM) material extrusion where a plastic wire is melted and deposited layer by layer to construct the part are being used to produce RF components and antennas. In the case of plastics, a conductive layer must be deposited onto the plastic to ensure conductivity. Recent work toward the development of horn antennas produced using SLS, SLA and extrusion methods has been accomplished. The methods have been shown to produce horn antennas capable of meeting a variety of applications in the test and measurement industry where accuracy and repeatability are key metrics. A comparison of methods is presented along with advantages and disadvantages. Performance data will be presented for some horns showing the capabilities of the various methods.

The Electric Multipole Produced by an SAE J2954 Wireless Power Transfer System Employing DD Couplers
James McLean, Robert Sutton, October 2023

Vehicular wireless power transfer (WPT) systems conforming to the SAE J2954 standard are thought to operate as inductive WPT systems. As such, they should be able to be accurately represented by a magnetic multipole source. For example, the magnetic field of the “circular” coupler, which is described in the SAE standard, can be represented by a combination of a vertical, linear magnetic quadrupole and a horizontal magnetic dipole. However, it has been recently shown that a significant conservative electric field exists in such a WPT system due to the multi-turn windings. This can lead to a significant electric multipole contribution, predominantly a vertical linear electric quadrupole for the circular coupler. In fact, the circular coupler electric field (not the magnetic field) is somewhat similar to that of a coaxial aperture. Here, we carry out a detailed analysis of the electric multipole representation of the “DD” coupler which is also described in the SAE standard. The analysis of the electric multipole of the DD coupler is more complex than that of the circular coupler. Because the DD coupler is composed of two side-by-side spiral windings, it is possible to obtain two different electric multipoles from configurations that produce nominally the same magnetic multipole and the same magnetic performance. Fortuitously, the configuration used in the DD coupler very nearly cancels the conservative electric field, the associated electric multipole, and the attendant emissions.

Optical Fiber Link Millimeter Wave Antenna Measurement System Using the Lock-in Amplifier
Satoru Kurokawa, Anton Widarta, Michitaka Ameya, Masanobu Hirose, October 2023

We have newly developed an optical fiber link millimeter wave band vector measurement system. The system consists of an optical fiber link millimeter wave transmission system, an optical fiber link millimeter wave receiving system, and the IF substitution method configuration using a lock-in amplifier (without a vector network analyzer). In this paper, we show the developed millimeter wave measurement system configuration and the millimeter wave measurement performance using the IF frequency measurement results.

Exploring the Effect of Varying Infill Densities and Patterns on Effective Relative Permittivity in 3D Printed Dielectric Substrates
Bibek Kattel, Winn Hutchcraft, Richard Gordon, October 2023

This paper explores the impact of varying infill densities for various infill patterns on the effective relative permittivity of 3D printed waveguide slabs. Previous studies have highlighted the substantial influence of infill patterns on the relative permittivity of substrates. The study aims to investigate the disparities in effective relative permittivity when diverse infill patterns are employed at various infill densities for multiple antenna substrates printed with identical parameters. Furthermore, this study examines the relationship between effective permittivities and infill densities for various infill patterns to identify suitable patterns for accurately estimating permittivity at lower densities. To accomplish this objective, dielectric slabs were 3D printed with a range of infill patterns and densities while maintaining consistent manufacturing parameters. The relationship between infill density and effective permittivity was analyzed for samples without the use of solid layers. The results revealed a linear behavior when solid layers were omitted during manufacturing. These findings underscore the critical role of infill pattern selection in determining material density and permittivity for antenna design and related applications.

Measurement Uncertainties in Outdoor Far-field Antenna Ranges
Edwin Barry, Pieter Betjes, Eric Kim, October 2023

Consolidated methodologies have long been established to assess measurement uncertainties in near-field antenna measurements. More recently, similar detailed approaches have been developed for compact ranges and adopted as standard practice. However, currently there is no analogous methodology for outdoor far field measurement facilities. This paper presents a framework for assessing the measurement uncertainties on an outdoor far-field elevated range. Various sources of uncertainty in an outdoor far-field range are identified, using the industry standard 18 term analysis for nearfield range assessment as a baseline. An example analysis based on an actual outdoor far-field range is presented. The uncertainty terms are quantified by analysis, observation, or measurement, and finally combined by the root sum squared method to arrive at the gain uncertainty and the -30 dB sidelobe level uncertainty.

Breaking the Limits: A High Performance Dual-Polarized Ultrawideband Antenna for Radar and Communication Systems
Syed Jehangir, Jorge Cerreno, October 2023

This paper presents the design of an ultrawideband (UWB) open-boundary dual-polarized quad-ridged horn antenna (QRHA) having an impressive 3-decades bandwidth from 1 to 32 GHz, making it an ideal choice for a wide range of applications in radars and communication systems. Its unprecedented bandwidth performance in a single and compact antenna geometry covers various frequency bands including L, S, C, X, Ku, and K. The ridge tapering profile of the proposed QRHA ensures excellent impedance matching, while the aperture matching prevents any phase distortion. The back-cavity design as well as cavity flaring is carefully optimized to achieve wideband performance along with no presence of pattern degradation specifically at the higher end of the frequency band. The antenna design exhibits a favorable impedance matching below -10 dB, well-matched copolar antenna patterns in the principal planes, and good crosspolarization (exceeding -20 dB) over a 3-decades bandwidth.

A Self-Contained and Airbourne SDR Transciever System for UAS based Antenna Pattern Measurement and Phased Array Radar Calibration Validation
Khuda Burdi, Antonio Segales, Caleb Fulton, Daniel Wasielewski, Igor Ivic, Jorge Salazar-Cerreno, Robert Palmer, October 2023

This paper discusses the novel development of a lightweight RF front-end system aimed at enhancing airborne antenna measurements in the far-field. The proposed system leverages advancements in software-defined radio (SDR) technology and high-performance RF front-end systems. While there are instances of SDR applications in UAS measurements, these systems are predominantly designed for anti-UAS and communication purposes, lacking focus on antenna and radar characterization. In contrast, the proposed system is purposefully tailored for RF applications, completely self-contained and airborne, possessing both RX and TX capabilities, and minimizing reliance on ground-based components. The system facilitates transmission and reception in both H- and V-polarization, employing two independent channels. Consequently, it allows for the simultaneous measurement of antenna or radar properties in both copolar (Cp) and cross-polar (Xp) orientations. The comparison between antenna measurements conducted within an anechoic chamber and those carried out utilizing the proposed UAS system demonstrates a substantial level of agreement.

A Self-Contained and Airbourne SDR Transciever System for UAS based Antenna Pattern Measurement and Phased Array Radar Calibration Validation
Khuda Burdi, Antonio Segales, Caleb Fulton, Daniel Wasielewski, Igor Ivic, Jorge Salazar-Cerreno, Robert Palmer, October 2023

This paper discusses the novel development of a lightweight RF front-end system aimed at enhancing airborne antenna measurements in the far-field. The proposed system leverages advancements in software-defined radio (SDR) technology and high-performance RF front-end systems. While there are instances of SDR applications in UAS measurements, these systems are predominantly designed for anti-UAS and communication purposes, lacking focus on antenna and radar characterization. In contrast, the proposed system is purposefully tailored for RF applications, completely self-contained and airborne, possessing both RX and TX capabilities, and minimizing reliance on ground-based components. The system facilitates transmission and reception in both H- and V-polarization, employing two independent channels. Consequently, it allows for the simultaneous measurement of antenna or radar properties in both copolar (Cp) and cross-polar (Xp) orientations. The comparison between antenna measurements conducted within an anechoic chamber and those carried out utilizing the proposed UAS system demonstrates a substantial level of agreement.

Characterizing Compact Antenna Test Range Using Advanced Computational Techniques
Venkata Bhyrava Murthy Devata, October 2023

Compact Ranges are widely used for antenna measurements across wide frequency ranges spanning frequencies as low as 350MHz to as high as 60GHz and above. Advances in electromagnetic (EM) simulations have significantly improved the design process for compact ranges, resulting in reduced costs. Characterizing compact range including the anechoic chamber is computationally very challenging in terms of computer memory and time. In this paper, we will present the full wave method, MLFMM for characterizing compact range without the chamber and application of asymptotic method, RL-GO to characterize the compact range inside the anechoic chamber.

The Impact of Rotating Linearly-Polarized Feeds on Circularly-Polarized Gain Uncertainty
Adam Mehrabani, Rob Mercer, Jeff Fordham, October 2023

This paper addresses the circularly-polarized (CP) gain uncertainty when using linearly-polarized feeds to obtain circular polarization in Compact Antenna Test Ranges. In particular, our emphasis is placed on quantifying the inaccuracy caused by deviations in amplitude and in phase of the two orthogonal linear measurements. This is of paramount importance especially for highly directive CP antennas operating at high frequencies in that the CP gain will be adversely impacted even by a small deviation from an ideal 90- degree rotation, as well as by a situation when the rotation may cause a slight boresight misalignment. To characterize the gain uncertainty, we look at ratio differences between the peak amplitude of the linear measurements, as well as cases when the phase shift of the two orthogonal linear measurements is no longer 90 degrees. The former is done through mechanical and electrical boresighting technique in the initial setting. The latter, which is the focus of this paper, is carried out through several case studies in practice mimicking some non-ideal 90- degree rotation settings.

Design and Validation of Quasi Ideal Ultra-Wideband 3dB/180° Couplers for High Precision Spherical Near-Field Probes
Andrea Giacomini, Francesco Saccardi, Vincenzo Schirosi, Antoine Raulais, Lars Foged, Jean-Marc Baracco, October 2023

Spherical Near Field (SNF) measurement systems are
primarily limited in usable bandwidth by the probe frequency
coverage. This limitation mainly arises from the presence of
higher-order azimuthal modes in the probe pattern [1]. In case of
electrically large or offset AUTs, such a limitation may be
overcome by a full probe correction algorithm for the NF/FF
transformation [2]. However, probes approximating first order
performance over the full bandwidth are generally preferred.
Traditionally, first-order probes based on geometrically
symmetric Ortho-Mode Junctions (OMJ) with externally
balanced feeding have been widely accepted. These probe designs
rely on couplers that provide equal amplitude and opposite phase
distribution at their output ports [3]. In this paper, the design
and validation of a novel 3dB/180° coupler is presented. The
concept is based on the natural anti-symmetric properties of the
electric field within the component, providing a quasi-perfect
amplitude and opposite phase distribution. To achieve these
properties, an architecture based on slot coupling is selected. The
design has been implemented in several frequency bands, from
UHF to Ku-band, as stand-alone cased components.
Experimental data at L/S-band is presented in this paper,
showing excellent performance in terms of matching, balance,
and isolation between output ports, well in-line with full-wave
electromagnetic predictions. In addition, the impact of the
coupler accuracy is also assessed on a relevant SNF test case.

Use of UASs for Outdoor Diagnostics of Large Antennas
Cosme Culotta-López, Snorre Skeidsvoll, Andrian Buchi, Joakim Espeland, October 2022

Unmanned aerial systems (UASs) enable the in situ diagnostic of antennas operated in outdoor environments. Additionally, their flexibility introduces the possibility of performing several diagnostic methods. In this overview work, the challenges of performing outdoor measurements with UASs are discussed and some of the possibilities they introduce are outlined. The main diagnostics tool when performing outdoor far-field measurements with UASs is the so-called raster scan. This is the two-dimensional scanning of a limited portion of the measurement sphere about the main lobe. From the information raster scans provide, it is possible to retrieve antenna parameters critical for the deployment of large antennas, such as the Side Lobe Level (SLL) in all directions, as well as the First Null Level. Additionally, assuming a fine scan, i.e., sufficient resolution, the interpolation of any 1D cut for diagnostics is possible. Once a problematic cut is interpolated and assessed, it can be measured using the UASs and increasing the measured angular range for further assessment. Assuming the measured large antennas are reflector antennas, the finding of a higher-than-expected SLL may point to a problem with the positioning of the feed. Measuring with UASs allows for an iterative measurement-and-adjustment process directly in situ, which guarantees that the antenna’s performance is within the boundaries required by either the application or regulations. Additionally, the flexibility of UASs provide further advantages, such as the assessment of the impact of environmental reflections in the radiation characteristics by flying along the radial component of the measurement sphere and assessing the measured ripple, using a method similar to the Voltage Standing Wave Ratio (VSWR) method used for the characterization of anechoic chambers. With this technique, the impact of the environment of candidates for an antenna deployment site can be assessed before the antennas are installed, thus supporting the choice process, and reducing the risk of malfunction. The discussion of the introduced techniques is supported by measurements, and future possibilities and advantages are studied.

On Convergence of the Upper Bound on the Ratio of Gain to Quality Factor
Alex J. Yuffa, Marc Andrew Valdez, Benoıt Derat, October 2021

An antenna’s practical far-field distance can be estimated from the upper bound on the ratio of its gain to quality factor. This upper bound is an infinite series that can be truncated based on the desired accuracy. We investigate the convergence properties of this bounding series. We find that the number of terms required for convergence depends on the antenna’s electrical radius in a way similar to the Wiscombe criterion used in Mie scattering theory. For typical experimental accuracy requirements, such convergence can significantly reduce the effective far-field distance.

Synthesis of a Phased Array with Planar Near-Field Techniques Based on Far-Field Measurements of a Sub-Array in a CATR
Bernd Gabler, Diego Lorente, L.G.T. van de Coevering, October 2021

Phased array antennas are often built from sub-arrays with identical or symmetrical layout. At an early project stage, performance verification measurements of the sub-array are valuable to proof the single module design. However, the characteristics of the final antenna are questionable without further processing. This work presents a concept that is based on far-field measurements of a sub-array in a Compact Antenna Test Range (CATR) in conjunction with planar near-field (PNF) processing to synthesize the entire phased array antenna characteristics. The procedure is explained with an example of a dual linear polarized L-band planar phased array antenna for an airborne synthetic aperture radar application. It is shown that the measured sub-array can be complemented by the synthesized twin to evaluate the characteristics of a final antenna that is not yet available in this form. The resulting performance of the synthesized entire phased array is presented and compared with simulations. The presented post-processing method would be beneficial to characterizing radiation patterns of large phased arrays by measuring only sub-arrays in a limited test-zone with any measurement principle.







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