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AMTA Paper Archive

Measurements of Incident Radio Frequency Power levels from the L3 Technologies ProVision Body Scanner for the National Academy of Science
Brian Kent, Tri Van, Ton Van, Kevin Hamblin, Jennifer Westhoven, October 2017

The Transportation Security Administration is tasked with the job of performing safety screening of millions of air travel passengers annually in a safe and efficient manner. One of the most widely deployed detection system is the L3 Technologies “Provision” body scanner, which utilizes millimeter wave radio frequencies (RF). Have you ever wondered what type and levels of RF energy are used to execute this routine security screening test? Recently, the Department of Homeland Security, Transportation Security Administration, tasked the National Academies of Science (NAS) to execute an updated safety analysis of the L3-Comm manufactured TSA ProVision Body Scanner units deployed in airports world-wide. In the process of executing their charter, the NAS realized there was very little peer-reviewed published data on calibrated field incident power within the ProVision scanner itself. While L3-Comm has their own factory acceptance program, the NAS wanted independent measurements executed on L3-Comm machines at four randomly selected airports. The NAS therefore contracted with the team of BerrieHill Research and Applied Research Associates to design a specialized field probe that could measure the RF emanations of the ProVision Units. This very challenging measurement environment required design ingenuity to fulfill the contract needs, since our team was not allowed to physically connect to any part of the ProVision machine. We had to place a field measurement device inside the unit where the passenger stands, and record all data over the air only. This paper will completely describe the BRC/ARA ProVision Scanner field probe measurement system, and present calibrated RF field measurements along with an uncertainty analysis of typical results.

A High Precision Group Delay Measurement Method for Circular Polarized High Gain Antennas
Georg Strauss, October 2017

In this contribution we demonstrate a method to measure the absolute Group Delay (GD) of a high gain dual feed offset reflector antenna for circular polarized signals in Ku- and S-band by which we reach a measurement accuracy better than 10 picoseconds. At first we discuss the definition and different possible measurement methods of GD. We specifically show that the utilization of the antennas phase centre does not lead to the demanded measurement accuracy. Instead we propose a measurement method that uses an electrically small Reference Antenna (RA). We use the measurement of the GD of the RA as a reference for the GD of the Antenna Under Test (AUT). Therefore the exact positions of the reference planes of the corresponding wave guide ports have to be ensured. For this we made use of a theodolite. These measurements must be performed in a Compensated Compact Range to meet the strict requirements of plane waves. Here the CCR of the Lab for Satellite Communication, Munich University of Applied Sciences was used. The GD of the (electrically small) RA is determined by measuring the GD of two identical RAs separated by an exact known free space distance and by referencing these measurements to the measured GD of the same arrangement, where the free space is bypassed by a long high precision rectangular wave guide with well-known dimensions. We demonstrate that by using a soft gating method the accuracy of the measurement results can be tremendously improved. Measurement results parametrized by the width of the gate window in the time domain are discussed. We further discuss the accuracy of the measurement results quantitatively and we especially show, that the influence of an antenna misalignment is negligible, as long the alignment error is smaller than the one dB power beam width. The measurement campaign was commissioned by the European Space Agency (ESA) to meet the requirements of the project Atomic Clock Ensemble in Space (ACES). By ACES a microwave link is used to compare the times given by different atomic clocks in space and on earth, so three ACES ground terminals were tested.

Comparison of Facilities for Low Level Coupling Tests in UAV EMC Certification
David Escot Bocanegra, Sergio Fernández Romero, Patricia López Rodríguez, Manuel Jesús Añón Cancela, David Poyatos Martínez, October 2017

Electromagnetic Compatibility (EMC) certification, aimed to ensure Air Vehicles (AV) safety, imposes the fulfilment of a number of requirements prior to flying in the airspace, in terms of usual Electromagnetic Interference (EMI) threats. Among them, and in relation to this study, the High-Intensity Radiated Field (HIRF) effects. Nowadays, Unmanned Aerial Vehicles (UAVs) regulations are being developed by several countries taking into account different safety requirements, proportionate to the risks. When the UAV risk is high due to its weight and dimensions, the certification requirements will be similar to those for manned aircraft. In this regard, there are two methods of evaluating the HIRF performance of a whole aircraft: traditional aircraft high level tests or alternative aircraft low level coupling tests. In any case, these kinds of tests need to be performed in dedicated test sites. Due to the size of aircraft, Open Area Test Sites (OATS) have been routinely used for these purposes. But they are outdoor facilities and suffer from intrinsic disadvantages, probably the most important one being the necessity of dealing with the vagaries of weather. As a result, alternatives to deal with EMC tests of such large items have been occasionally sought. This paper aims at comparing the results obtained when measuring part of the fuselage of an actual UAV in two test sites, an OATS and a Reverberation Chamber (RC). Two aircraft low level coupling tests are studied in depth, namely, Low Level Direct Drive (LLDD) and Low Level Swept Fields (LLSF) tests. In the former, the coaxial return technique was employed and, consequently, the reverberation chamber was used only as a mere shelter being the aim to confirm that the RC structure do not affect the results and good agreement with OATS is obtained. On the other hand, the LLSF tests were conducted in the RC with the paddle in stirrer mode and compared with the worst-case result obtained for several illuminations in OATS.

Radiation Center Estimation from Near-Field Data Using a Direct and an Iterative Approach
Cosme Culotta-López, Kui Wu, Dirk Heberling, October 2017

Spherical Near-Field (SNF) measurements are an established technique for the characterization of an Antenna Under Test (AUT). The normal sampling criterion follows the Nyquist theorem, taking equiangular samples. The sampling step size depend on the smallest sphere that, centered in the measurement’s coordinate system, encloses the AUT, i.e. the global minimum sphere. In addition, a local minimum sphere can be defined as the sphere with minimum radius which, centered in the AUT, encloses it alone. The local minimum sphere is always equal or smaller than the global minimum sphere, being equal when the AUT is centered in the measurement’s coordinate system. It is assumed that the local minimum sphere’s center coincides with the radiation center. Furthermore, it is possible to compute a Translated Spherical Wave Expansion (TSWE) centered in the local minimum sphere, thus needing less measurement points, as long as the relative position of its center is known. Due to practical reasons, it is not always possible to easily locate the radiation center. In this paper, the relative position of the radiation center of an AUT with respect to the measurement's coordinate system’s center is estimated from SNF data using two approaches. The first approach takes the phase center as an estimation of the radiation center and is based on the method of moving reference point, strictly valid for the far-field case, analyzing its error at different near-field distances. The second approach is based on a spherical modes' spectrum analysis: the closer the AUT’s radiation center is to the coordinate system's center, the larger the power fraction in the lower modes will be. The proposed algorithm iteratively displaces the SWE and checks the power in a predefined number of modes until the convergence criterion is fulfilled. It is important to note that no near-field to far-field transformation is used, for the less measurement points taken do not allow it. A thorough analysis of the estimation error is done by simulation for different cases and antennas. The estimation error of both methods is compared and discussed, highlighting the convenience of each method depending on the requirements.

Nearfield Antenna Measurements over Seawater – Some Preliminary Thoughts
David Tonn, October 2017

The principles of near-field antenna measurements and scanning in Cartesian and spherical coordinates are well established and documented in the literature, and in standards used on antenna ranges throughout government, industry, and academic applications. However the measurement methods used and the mathematics that are applied to compute the gain and radiation of the pattern of the test antenna from the near-field data assume typically that the antenna is operating in free space. This leaves several questions open when dealing with antennas operating over a lossy ground plane, such as the ocean damp soil, etc. In this paper, we shall discuss some of the motivation behind an examination of the physics and mathematics involved in performing a near-field antenna measurement over a seawater ground plane. Examples of past work in this are shall be discussed along with some of the challenges of performing far field antenna measurements in the presence of the air-sea interface. These discussions lead to some fundamental questions about how one defines gain in this environment and whether or not a near field approach could be beneficial. This will lead to some discussion of when and how the existing modal field expansions used in near-field measurements may need to be adjusted to account for the presence of the ground plane created by the ocean surface. An example of the limiting case of an antenna operating over a metallic ground plane will be discussed as a stepping stone to the more general problem of an antenna operating over a lossy ground plane.

Cost Functions in Near-Field Spherical Scanning Data Processing Algorithms
Michael Francis, Ronald Wittmann, October 2017

Spherical wave coefficients are chosen to minimize a cost function that is a norm of the residual of the fit. For example, in standard orthogonality-based processing algorithms [1], the cost function is an integral (over 4 p steradians) of the squared amplitude of the difference between actual measurements and predicted values. Some recent work [2,3] at NIST has led to the use of discrete norms where the integral is replaced by a weighted sum. We explore issues regarding the choice of these weights, the relative performance of different weighting schemes, and the relation between the continuous and discrete cases. These norms are mathematically equivalent if there is a solution with zero residual. In practice, we have observed noticeable variation due to the presence of measurement errors, including multiple reflections, room reflections… Also, different weighting schemes are associated with widely varying condition numbers. When the condition number is large, small measurement errors can lead to large errors in the result. Additionally, we show that the integral cost function mentioned above can be reduced to a discrete quadrature. M.H. Francis and R.C. Wittmann, Chp. 19, “Near-Field Scanning Measurements: Theory and Practice” in Modern Antenna Handbook, ed. C.A. Balanis, John Wiley & Sons, 2008. R.C. Wittmann, B.K. Alpert, M.H. Francis, “Near-field, spherical-scanning antenna measurements with nonideal probe locations,”IEEE Antennas and Propagat., vol. 52, pp. 2184 – 2186, August 2004. R.C. Wittmann, B.K. Alpert, M.H. Francis, “Near-field antenna measurements with nonideal measurement locations,”IEEE Antennas and Propagat., vol. 46, pp. 716 – 722, May 1998.

Assessment of a 3D-Printed Aluminum Corrugated Feed Horn at 118.7503 GHz
Joshua Gordon, Lavanya Periasami, Albin Gasiewski, David Novotny, Michael Francis, Ronald Wittmann, Jeffrey Guerrieri, October 2017

We investigate all-metal 3D printing as a viable option for millimeter wave applications. 3D printing is finding applications across many areas and may be a useful technology for antenna fabrication. The ability to rapidly fabricate custom antenna geometries may also help improve cub satellite prototyping and development time. However, the quality of an antenna produced using 3D printing must be considered if this technology can be relied upon. Here we investigate a corrugated feed horn that is fabricated using the powder bead fusion process for use in the PolarCube cube satellite radiometer. AlSi10Mg alloy is laser fused to build up the feed horn, including the corrugated structure on the inner surface of the horn. The intricate corrugations, and tilted waveguide feed transition of this horn made 3D printing a compelling and interesting process to explore. We will discuss the fabrication process and present measurement data at 118.7503 GHz. Gain extrapolation and far-field pattern results obtained with the NIST robotic antenna range CROMMA are presented. Far-field pattern data were obtained from a spherical near-field scan over the front hemisphere of the feed horn. The quasi-Gaussian HE11 hybrid mode supported by this antenna results in very low side lobe levels which poses challenges for obtaining good SNR at large zenith angle during spherical near field measurements. This was addressed through using a single alignment and electrical calibration while autonomously changing between extrapolation and near-field measurements using the robotic arm in CROMMA. The consistency in parameters between extrapolation and near-field measurements allowed the extrapolation data to be used in-situ as a diagnostic. Optimal near-field scan radius was determined by observing the reflection coefficient S11 during the extrapolation measurement. The feed horn-to-probe antenna separation for which |S11| was reduced to 0.1 dB peak-to-peak was taken as the optimal near-field scan radius for the highest measurement SNR. A comparison of these measurements to theoretical predictions is presented which provides an assessment of the performance of the feed horn.

Determination of the Far Field Radiation Pattern of an Antenna from a Set of Sparse Near Field Measurements
Scott Kordella, Kenneth Grimm, November 2016

This work introduces a new technique in electromagnetic antenna near-field to far-field transformation (NF/FF). The NF/FF transformation is based on the solution of an inverse problem in which the measured NF and predicted FF values are attributed to a set of equivalent electric and magnetic surface currents which lie on a convex arbitrary surface that is conformal to the antenna under test (AUT). The NF points are conformal to the AUT, reducing the number of samples and relaxing positioning requirements used in conventional spherical, cylindrical and planar NF/FF geometries. A pseudo inversion of the matrix representing the mapping of the equivalent sources into the near-field samples is obtained by using the singular value decomposition (SVD). The SVD is used to form an approximation of the inverse of the matrix. This inverse, when multiplied by the NF measurement vector, solves for the efficiently radiating components of the current, and not the essentially non-radiating components of current which are not visible in the measurements. The inversion technique used is robust in the presence of measurement noise and provides a stable solution for the unknown currents. The FF is computed from the currents in a straightforward manner. The work develops the theoretical foundation for the approach and investigates the FF reconstruction accuracy of the technique for a test case. Approved for Public Release; Distribution Unlimited. Case Number 16-0884 The author's affiliation with The MITRE Corporation is provided for identification purposes only, and is not intended to convey or imply MITRE's concurrence with, or support for, the positions, opinions or viewpoints expressed by the author.

Practical Considerations for Coordinate System Rotations in Mode-Space
Ryan Cutshall, Jason Jerauld, Justin Dobbins, November 2016

Rotating the coordinate system of an antenna pattern can be problematic due to the need to interpolate complex data in spherical coordinates. Common approaches to 2D interpolation often introduce errors because of polarization discontinuities at the spherical coordinate system poles. To overcome these difficulties, it is possible to transform an antenna pattern from field-space into spherical mode-space, perform the desired coordinate system rotation in mode-space, and then transform the modes in the rotated coordinate system back into field-space. This method, while more computationally intensive, is exact and alleviates all of the interpolation-related issues associated with rotations in field-space. Although rotations in mode-space have been implemented in commercially available software (e.g., the ROSCOE algorithm provided by TICRA), these algorithms may not be well understood by the general antenna measurement community. Therefore, the first goal of this paper is to present an easy-to-understand algorithm for performing rotations in mode-space. Next, the paper will address the challenge of computing the rotation coefficients, which are required by the mode-space coordinate system rotation algorithm. Although J. E. Hansen presented a method for recursively computing the rotation coefficients, this method is numerically unstable for large values of N (where N is the upper limit of the polar index). Therefore, this paper will present a numerically stable method for the recursive computation of the rotation coefficients. Finally, this paper will show the relationships between Euler angles and both Az-over-El angles and El-over-Az angles. These relationships are quite useful because it is often desired to rotate an antenna pattern based on Elevation and Azimuth angles, whereas the inputs for the mode-space rotation algorithm are Euler angles. Knowing these relationships, the Euler angles may be computed from the Azimuth and Elevation angles, which can then be used as the inputs to the mode-space rotation algorithm.

Phase Error Characterization of a Space-Fed Array
Brian Holman, Jacob Houck, Philip Brady, November 2016

GTRI has been developing a method for insertion phase calibration, as discussed in the paper “Insertion Phase Calibration of Space-Fed Arrays,” which was presented at AMTA in 2015 [1]. This method has been implemented to characterize the phase response of phase shifters in a system currently under fabrication at GTRI. One of the primary requirements for the phased-array antenna of this system is a maximum RMS phase error. The RMS phase error for this array is influenced by a variety of error sources, including phase shifter quantization, beam steering computer (BSC) algorithmic error, phase shifter unpredictability error, test fixture induced error, phase shifter thermal drift, and phase shifter frequency dependency. Each of these error sources has been categorized as either a non-deterministic error, whose behavior can be statistically characterized but not calibrated out, or as a deterministic error, whose behavior can be characterized and potentially calibrated out. The non-deterministic errors include element unpredictability, which is induced by the inability of an individual phase shifter to precisely repeat a given phase command, and errors induced by the calibration test fixture itself. The deterministic errors include phase shifter quantization error, which is a function of the phase state bit precision, BSC algorithmic error, which is driven by the numerical preciseness of calculation of the commanded phase states for each element, thermal driven phase drift, and phase shifter frequency dependency across the band of operation. To calibrate the insertion phase and phase-state response curves for all phase shifters used in the system, a custom-built calibration fixture was constructed into a septum wall that separates two semi-anechoic chambers. The realized phase-error budget of the system under fabrication was affected directly by the accuracy of both the calibration method and this fixture. We will present our analysis of all phase-error sources as they contribute to the overall phase-error design goal of the system. We have shown how the design and implementation of both the calibration fixture and methodology meet that goal.

An Overview of Atom-Based SI-traceable Electric-Field Metrology
Joshua Gordon, Christopher Holloway, Matthew Simons, November 2016

We present an overview of radio frequency (RF) electric-field measurements using Rydberg atoms. This technique exploits the rich resonance response of these atoms which can occur across a large frequency range from about 500 MHz-500 GHz. This measurement utilizes alkali atoms such as rubidium and cesium atoms confined in a glass vapor cell that are excited optically by to different lasers to high energy Rydberg states. Once in the Rydberg state the atoms exhibit a significant response to RF fields. The presence of the RF field alters the optical spectrum of the atoms, which can be interrogated to determine the RF field strength. One of the main goals of this work is an atomic standard measurement of RF fields that is intrinsically calibrated, directly linked to the SI and atomic structural constants.

The Measurement of Horizontal Magnetic Dipole Moment at a Conducting Ground Plane Using a Modified Van Veen Loop
James McLean, Robert Sutton, November 2016

Magnetic Field Wireless Power Transfer (MF-WPT) systems such as those used in vehicular applications produce extraneous emissions not only at the fundamental frequency (typically in the LF range) but also, due to rectifier harmonics and short-time-scale ringing in the H-bridge and rectifier circuits, over a broad spectrum which extends well up into the HF frequency range.  Thus, characterization of the emissions from such a system must cover this broad frequency range.  The Van Veen Loop or Loop Antenna System has been successfully used to characterize some MF-WPT systems.  However, typically the couplers in such a system are situated essentially at ground level.  One problem with using the conventional Van Veen Loop to characterize an MF-WPT system is that there is some possibility that removing the couplers from the ground will modify the current distribution in them and hence change the extraneous field.  Thus, it would be useful to determine the net magnetic dipole moment of an MF-WPT system in situ.  In the case of conducting ground, the vertical magnetic dipole moment is nearly completely canceled by its image.  The net horizontal magnetic dipole moment is thus the predominant source of the far electromagnetic field.  Therefore, we consider measuring the two orthogonal components of the net horizontal dipole moment of an MF-WPT system situated at conducting ground. The Van Veen Loop can be adapted to operation at a conducting ground plane by taking advantage of the images of the two component loops with horizontal axes. With this in mind, a system has been developed which is essentially half of a Van Veen loop.  That is, it consists of two orthogonal shielded “half” loops which terminate at the ground plane. We analyze this unconventional Van Veen Loop and also provide experimental verification of its performance in the time and frequency domains.  Finally, we provide details of the design which is similar to, but not the same as, that given in the CISPR 16-1-4 standard.

Spherical Field Transformation for Hemispherical Antenna Measurements above Perfectly Conducting Ground Planes
Raimund Mauermayer, Thomas Eibert, November 2016

The spherical multipole based near-field far-field transformation is extended to near-field antenna measurements above a perfectly electrically conducting (PEC) ground plane. As the effect of the ground plane is considered in the transformation by applying the image principle to the spherical modes radiated by the device under test (DUT), the near-field measurement points above the ground plane are sufficient to fully characterize the radiation behavior of the DUT above PEC ground. The nonequispaced fast Fourier transform (NFFT) is employed in the forward operator of the inverse problem in order to apply the transformation to e.g. spiral scans which are favorable to large and heavy scanner systems. If the elevation axis is located above or below the ground plane, an additional translation operator is integrated into the transformation to consider such an offset in the mechanical system. The proposed method is applied to synthetic and simulated automotive antenna near-field data in order to show its effectiveness.

Time Gating Based on Sparse Time Domain Signal Reconstruction from Limited Frequency Domain Information
Raimund Mauermayer, Thomas Eibert, November 2016

Time gating is one of the most widespread techniques to suppress the effect of unwanted echoes on antenna measurements. It just requires the measurement of the antenna under test (AUT) for a carefully chosen bandwidth and frequency step size and the isolation of the direct AUT signal contribution from the echo contribution in time domain is quite intuitive. Although a frequency sweep is usually fast compared to the axes movement, it might become the speed limiting factor for large measurement bandwidths. Thus, time gating techniques that need a minimum bandwidth are beneficial. Therefore, a gating method is presented that reconstructs a time domain signal with high resolution from a minimum measurement bandwidth based on the assumption that the time domain signal is sparse, i.e. it mainly consists of samples with low amplitude and only few samples with high amplitude which are related to the peaks of the direct and the echo signal. The effectiveness of the proposed method is compared with the well known fast Fourier transform (FFT) and matrix pencil method (MPM) based techniques using echoic near-field antenna measurement data.

Gain Comparison of 3D Printed Horns and an Electroformed Horn of the Same Size and Shape
Michael Francis, David Novotny, Joshua Gordon, Alexandra Curtin, Ronald Wittmann, November 2016

The National Institute of Standards and Technology has used the three-antenna extrapolation method to determine the on-axis gain of several standard gain horns in the WR8 frequency band.  All the horns, but one, are pyramidal horns of similar size and shape and were manufactured using a 3D printing method.  The last horn was electroformed. The gains of these horns are compared to each other and to the theoretical value.  Our preliminary measurement results show that the electroformed horn has a better gain than that of the 3D printed horns and is closer to the theoretical gain value.  A visual inspection of the 3D printed horns finds that the surface of these horns is significantly rougher than that of the electroformed horn.  We believe that this leads to larger ohmic losses in the 3D printed horns than in the electroformed horn.  The directivity of the 3D printed horns and the electroformed horn are nearly the same. The extrapolation method, which is used for determining the gain, fits the power received as a function of separation distant to a power series in 1/(separation distance)n.  The leading term in the power series is proportional to the pair gain (sqrt(G_i*G_j)).  By making measurements of three antennas in three unique pairs (1 vs 2, 1 vs 3, and 2 vs 3).  It is possible to determine the gain of all three antennas without knowing any of them to begin with. One requirement is that one of the three antennas be reciprocal.

A Radar Echo Emulator for the Evaluation of Automotive Radar Sensors
Domenic Belgiovane, Chi-Chih Chen, J. Landon Garry, November 2016

Automatic emergency braking (AEB) and collision imminent braking are beginning to be implemented by major automotive manufactures. AEB systems utilize automotive radar sensors operating in the 77 GHz frequency band for target detection. These said systems are capable of providing warning directly to the vehicle driver and when necessary apply automatic emergency braking. The effectiveness of such systems need to be accurately tested using standards and test procedures that are yet to be agreed upon among international automobile industry and government agencies. The Euro NCAP vehicle target (EVT) is the current European standard for AEB testing scenarios. The main goal of this research effort was developing a compact W-band radar echo emulator (REE) to be used for evaluating automotive pre-collision systems (PCS) operating in the 77 GHz frequency band. The proposed REE is capable of receiving radar signals from the PCS radar mounted on the vehicle under test (VUT) and then transmits modified radar signals back to PCS radar bearing the similar signatures (temporal, spectral, and pattern) as the Euro NCAP Vehicle Target (EVT). REE eliminates the need for the front vehicle target to produce radar responses which is currently accomplished with complicated arrangement of RF absorbers and reflectors as in the EVT and other vehicle surrogates. The adoption of REE means that the vehicle target only needs to bear optical signatures similar to an actual vehicle, and thus can be made with a much simpler balloon structure. Measurements present for the characterization of the Euro NCAP EVT over distance as well as the calibrated radar cross section (RCS). From this simply target model the REE echo power is empirically determined. The REE solution to PCS testing scenarios offers an easily adaptable return power various targets can be emulated with a single module.

Far Field Uncertainty due to Noise and Receiver Nonlinearity in Planar-Near Field Measurements
Serge Balma, Dominique Picard, Pascal Meisse, November 2016

The uncertainty of the far field, obtained from antenna planar near field measurements, against the dynamic range is investigated by means of statistical analysis. The dynamic range is usually limited by the noise floor for low level signals and by the receiver saturation for high level signals. The noise level could be important for high measurement rate, which requires the usage of a high signal level to ensure a sufficient signal to noise ratio. As a result the nonlinearities are increasing, thus a compromise must be accomplished. To evaluate the effects of the limited near field dynamic range on the far field, numerical simulations are performed for dipoles array. Initially, the synthetic near field data corresponding to a given antenna under test were generated and directly processed to yield the corresponding far field patterns. Many far field parameters such as gain, beam width, maximum sidelobe level, etc. are determined and recorded as the error-free values of these parameters. Afterwards, the synthetic near field data are deliberately corrupted by noise and receiver nonlinearities while varying the amplitude through small, medium and large values. The error-corrupted near field data are processed to yield the far field patterns, and the error-corrupted values of the far field parameters are calculated. Finally, a statistical analysis was conducted by means of comparison between the error-corrupted parameters and the error-free parameters to provide a quantitative evaluation of the effects of near field errors on the different far field parameters.

Radar Echoes from Metal Spheres Large and Small
Pax Wei, November 2016

Wave scattering from a perfectly conducting sphere provides an important example for theoretical studies as well as RCS calibrations [1, 2].  At the Boeing 9-77 Range and the Millimeter Wave Range in Seattle, we measured spheres of large and small diameters, supported by strings or a foam tower, and through a wide range of frequencies.  In addition to co-polarized calibration, the emphasis was also on uncertainty analysis in order to verify that the experiments carried out under different conditions were mutually consistent [3].  Aside from the well-defined conditions for an indoor range, metal spheres may be dropped from the air free fall while being measured [4].  A news article on January 5, 2016, reported that three metal spheres were picked up in three provinces in northern Vietnam [5].  Though details of the experiments were obscure, from the pictures they happened to correspond to spheres of sizes from large to small.  Based on our experiences, some speculation will be discussed.  References [1]. E. F. Knott, "Radar Cross Section Measurements," (Van Nostrand Reinhold,  New York, 1993), pp. 176-180, (on spheres and the Mie series).   [2]. E. F. Knott, E. F. Shaeffer, and M. T. Tuley, "Radar Cross Section," (Artech House,      2nd ed, 1993), pp. 86 & 234-235, (on creeping waves).  [3]. P. S. P. Wei, A. W. Reed, C. N. Ericksen, and J. P. Rupp, “Uncertainty Analysis and      Inter-Range Comparison on RCS Measurements from Spheres,” Proc. 26th AMTA,      pp. 294-299 (2004).   [4]. “Mysterious silver balls fall down on town; can the black helicopters be far behind?”   By Steve Vogel, The Seattle Times, August 7, 2000, (from the Washington Post).  [5]. “3 mysterious spheres fall onto 3 Vietnam provinces,”  Tuoi Tre,  Tue, 05 Jan 2016.  http://www.sott.net/article/309800-3-mysterious-spheres-fall-onto-3-Vietnam-provinces

Implementation and Testing of Engineered Anisotropic Dielectric Materials
David Tonn, Susan Safford, Michael Lanagan, Eugene Furman, Stephen Perini, November 2016

Several instances in antenna design are known where an anisotropic material is useful ; however, finding a naturally occurring anisotropic material with the required dielectric tensor is often an impossibility. Therefore, artificially engineered anisotropic dielectric materials must be designed, tested, and implemented. In a previous paper by the authors [1], the design and initial measurement of an anisotropic material in Cartesian coordinates was presented along with predictions of how the material could be used to extend the bandwidth of a simple antenna structure.             In this paper we shall present the final implementation of the anisotropic material (with a tensor implemented in cylindrical coordinates) along with data on the material properties, the resulting antenna bandwidth, and radiation pattern. Design considerations for implementation of this approach shall be discussed along with practical limitations. Data shall also be presented on an unexpected result showing that that a reduced volume of anisotropic material produces favorable results. Measured data shall be compared with values predicted using finite difference time domain (FDTD) software and applications of this new broadband antenna for range operations will be discussed. [1]. D. Tonn, S. Safford, M. Lanagan, E. Furman, S. Perini, “DESIGN AND TESTING OF LAYERED ANISOTROPIC DIELECTRIC MATERIALS”, AMTA 2015 Proceedings, Long Beach CA, October 2015.

Effective Numerical Methods for Installed Performance of Antenna Arrays on Electrically-Large Platforms
Derek Campbell, C.J. Reddy, November 2016

Wireless connectivity is rapidly expanding in both popularity and potential. Incorporating antenna arrays on both ends of the wireless channel realizes this potential by facilitating beam steering and increased directivity. From an operations vantage point, these capabilities reduce transmit power, increase data rates, and extend communication range. Antenna arrays also facilitate forming nulls toward antagonistic regions to hide information and thwart easily accessible jamming devices. These performance characteristics of antenna arrays address several critically important challenges for Unmanned Aerial Vehicle (UAV) operation, which is becoming attractive in both military and commercial sectors. Maintaining wireless communication channels over extended ranges that can potentially cross into antagonistic regions helps accomplish precise, adaptable mission objectives. In addition, efficiently utilizing power, a scarce commodity typically drawn from solar panels, facilitates extended flight durations. Finally, the reduced transmit power also reduces the aircraft weight, which can further extend flight duration. Although antenna arrays offer extensive advantages, the final design must account for the presence of the aerial platform including other electronic systems. Strong mutual coupling can then result from operating multiple wireless systems within a physically confined space. In addition, the surrounding environment can change the electrical characteristics of the antenna (e.g. input impedance and radiation pattern). Analyzing these electrical characteristics on a physically-confined platform becomes an electrically-large problem when operating a communication channel over the 2.4 GHz ISM band. Simulating the installed performance potentially requires significant computational resources unless research is conducted to understand the trade-offs between numerical methods in existing commercial software. The installed performance of an antenna array on an electrically-large platform can then be optimized in the most efficient manner. In this paper, we demonstrate a process that efficiently navigates the typical trade-offs engineers encounter when conducting an antenna placement study. This process involves designing a conformal antenna array in an isolated environment, analyzing potential installation locations and further optimizing the antenna array for the chosen location.







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