AMTA Paper Archive
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Antenna Radiation Pattern Measurements Using a Reverberation Chamber
This paper investigates the use of a reverberation chamber for antenna radiation pattern measurements allowing for significant cost reduction compared to anechoic environments. Our method utilizes averaging of paddle measurements to replicate anechoic data. We discuss both a correlation experiment, to determine how many degrees the reverberation paddle must rotate to create an uncorrelated measurement based on a 0.5 correlation threshold, and a radiation pattern measurement. Two matched horn antennas are used and operated between 1 GHz and 18 GHz. Good agreement is found between our measurements taken in a reverberation chamber and those taken by the manufacturer of the antenna in an anechoic chamber. We find that the main lobe radiation pattern of our antenna can be estimated with more certainty than the back-lobe radiation using a reverberation chamber. The goal is to use this simple and cost-effective method to determine radiation patterns for embedded antennas with unknown patterns, such as those within wireless devices.
Spot-Probe Reflectometer Measurements of Geological Core Slab Samples
Rock core specimens collected during surveys for oil drilling have, in a standard form, a 4" diameter. Cores are cut in half or in 1/3-2/3 sections to provide core slab. We developed a measurement procedure based on spot probe illumination to characterize geological and/or geochemical properties of core slab specimens via their complex permittivity for frequencies between 2.5 GHz and 20 GHz. Conventional reflectometer methods are based on illumination of a thin slab of air-or metal-backed material. However, in this case only the front surface is flat and the back surface is semicircular. A measurement method was developed based on time-domain gating to separate the back-surface reflection from that of the front. Material inversion is then based on the amplitude and phase of the reflection just from the front surface. This paper presents details of the calibration for this reflectometer measurement method, along with example measurements of core slab materials. Two different inversion methods are applied to these measured data. The first is a more conventional frequency-by-frequency method for inverting complex permittivity from the amplitude and phase of the reflection. The second method applies a physical model, the Debye relaxation model, to the data. This model-based approach minimizes the errors from edge diffraction from the small sample size.
Evaluation of the Monostatic-Bistatic theorem applied to the radar signature of aerial platforms in low frequency
In this paper, we explore the capabilities of the Monostatic-Bistatic Theorem (MBT) applied to Radar Cross Section (RCS) in low frequency. Originally, the validity of this theorem has been shown in high frequency for targets whose RCS is produced by elementary interactions (specular reflection in particular). We are interested in aerial platforms and in particular some Low Observable targets that have relatively "pure" geometries limiting the presence of complex interactions. Several variants of the MBT from the field of electromagnetism  and acoustics  are used. Their performances are compared from data obtained from a MoM method that is recognized to produce accurate scattering data. To highlight the discrepancies produced by the different variants, we use both a metric to compare the quality of the bistatic holograms obtained and also radar imaging which allows locating the areas of the target where the echoes are not correctly restored.
Precision Optical Antenna Alignment System for Tracking Antennas in 6-DOF
We present on an all-optical spatial metrology system , the PiCMM, that aids in the alignment and tracking of antennas with accuracies on the order of 25 microns and 0.01 deg. This system speeds up millimeter-wave antenna alignment, does not require contact, and links spatial measurements to a laser tracker world coordinate frame. An automated Pixel Probe and dark-field imaging are used to directly measure the aperture geometry and its pose. These measurements are absolute in the world-frame of a laser tracker and associated coordinate metrol-ogy space of the antenna scanner. Thus, aperture geometries can be linked directly to any laser tracker target (i.e. 6DOF, 3DOF) and data such as that used to calibrate positioner kinematics. For example, the links and joints defining the Denavit-Hartenberg kinematic model of a robotic arm scanner. The new automated aspect of the system reduces alignment time to under an hour. The synergy with laser tracker targets allows for a high level of repeatability. Furthermore, antennas can be exchanged or realigned in the antenna scanner autonomously because antenna geometry and kinematic models reside in the same laser tracker coordinate metrology space.
Improved Nearfield Gain Measurement of High Gain Antennas Using Directivity and Loss Technique
Antenna gain is the product of directivity and antenna loss. Antenna gain is typically measured by comparing the antenna under test (AUT) to a standard gain horn (SGH) or direct gain measurement using a calibrated probe. This requires an accurate account of power into the AUT and SGH, the loss of all test cables and switches must be measured to obtain an accurate AUT gain. Additionally, SGH calibration uncertainty reduces the quality of the measurement. The gain measurement technique describe here exploits the near-field range capability of accurately producing the pattern of high gain antennas. The near-field range allows the full wave capture of antenna aperture fields and transformation to the far-field with high resolution. The new technique uses the directivity obtained by integrating the far-field pattern, accounts for the spill-over energy not measured by the near-field range, and uses measured network losses of the AUT. It does not require measured losses of test cables and switches. Since AUT losses are typically measured as part of antenna integration the technique reduces overall measurement burden. Accurate calculation of spill-over energy is the key to success. The technique has been shown to yield better accuracy than the typical gain calibration method for multi-beam high gain antennas.
Estimation of the Realistic Ground Effect in Free-Space Automotive Measurements
Testing of automotive antennas are commonly performed in large Spherical Near Field (SNF) ranges [1-3] able to host the entire vehicle to test the effect of the antenna coupling with the structure . The impact of a realistic ground, such as asphalts or soil, on the radiation performance of the vehicle mounted antennas is often a desired information. As long as the free-space response of the vehicle is available, such information can be obtained with fairly good accuracy considering post-processing techniques based on the Image Theory (IT). Automotive systems with absorber material on the floor  are thus ideal for estimating such effects because the free-space signature of the vehicle is directly measured and because the radiation pattern is usually available on more than just a hemisphere. In this paper an IT-based technique which allows for the estimation of a realistic ground is proposed and validated with simulations where the measurement setup of a typical multi-probe free-space automotive system is emulated. The impact of the truncation of the scanning area is analyzed in detail showing how advanced post-processing techniques [4-6] can be involved to mitigate the truncation errors and thus obtain a better estimation of the realistic ground effect.
Extending the Scan Volume of Planar Near-Field Scanners with AUT Rotation
Planar near-field ranges are popular facilities to evaluate far-field antenna patterns. These ranges typically have the scanner plane parallel to the Antenna Under Test (AUT). Having the scanner plane parallel to the AUT can limit the maximum far-field angles that can be properly measured due to the mechanical extents over which the range can accommodate. This paper summarizes a test approach where the AUT is rotated in the near-field such that sufficient energy is concentrated within the range extents, ultimately resulting in an accurate far-field pattern. Measured results will be shown which demonstrate the limitations of the current testing approach, as well as the benefits of the near-field rotation approach.
DTU-ESA Spherical Near-Field Antenna Test Facility -2017/18 Upgrade and Validation Measurements with the DTU-ESA VAST12 Antenna
This paper documents the various elements of the 2017/18 upgrade and presents results from the performance validation measurements with the DTU-ESA 12 GHz Validation Standard antenna conducted before and after the upgrade. The upgrade concerned several major improvements to the building infrastructure, the ventilation system, the antenna positioner, and the probe positioner. The validation measurements involved the averaging of measurements at different distances between the antenna under test and the probe to compensate the multiple reflections between these. This in turn necessitated the investigation of the compensation of the system drift between the measurements and of the sensitivity of the probe calibration to the position of the probe on the probe positioner.
Power Density Measurement at 5G Millimeter-Wave Using Inverse Source Method
5G user equipment, such as mobile terminals and tablets shall comply with radio frequency (RF) safety guidelines. At millimeter-wave frequencies, human exposure to RF electromagnetic fields (EMFs) is evaluated in terms of incident power density, i.e., free space Poynting vector. As, the electrical size of mobile terminals increase with higher frequencies, longer testing times are needed to determine power densities in the proximity of devices by traditional scanning. A new approach to accurately determine the power densities in close vicinity to a device is based on standard near-field measurements and processing by the inverse source method. This method is faster, simpler, and thus desirable compared to dedicated scan on a device dependent surface. The new method uses the capabilities of the equivalent current expansion to determine the power density by NF/NF transformation on any surface and at any distances according to the safety normative. The method was presented on a device in  by comparison to simulated power densities. Although correlations were promising, some discrepancies were likely due to the approximated numerical model of the device. In this paper, the SH4000, Dual Ridge Horn, with well-known full wave model is investigated to validate the power density determination against accurate simulations.
Validation of Additive Manufacturing for Broadband Choked Horns at X/Ku Band by Extensive Antenna Measurements
Additive manufacturing has become a popular alternative to traditional CAM techniques, as it has reached a suitable maturity and accuracy for microwave applications. The main advantage of the additive technologies is that the manufacturing can be performed directly from the 3D CAD model, available from the numerical simulation of the antenna, without significant modifications. This is a highly desirable feature, in particular for time and cost critical applications such as prototyping and manufacturing of small quantities of antennas. Different 3D-printing/additive manufacturing technologies are available in industry today. The purpose of the paper is an investigation on the accuracy and repeatability of the Selective Laser Melting (SLM) manufacturing technique applied to the construction of a batch of 15 broad band fully metallic chocked horns, operating at X/Ku band, manufactured in parallel. Manufacturing accuracy and repeatability has been evaluated using RF parameters as performance indicators comparing measured data and high accuracy simulations. The radiation patterns have been correlated to the numerical reference using the Equivalent Noise Level, while manufacturing repeatability is quantified on input matching by defining an interference level. These indicators have also been compared to state-of-the-art values commonly found for traditional manufacturing.
Modeling of Tapered Anechoic Chambers
A hybrid method that combines the finite element method (FEM), the Floquet mode analysis and the shooting and bouncing ray method (SBR) is presented to solve the quiet-zone field in large tapered anechoic chambers. In the method, the field equivalence principle is employed to replace the throat of the tapered chamber by a set of equivalent electric and magnetic currents. The Floquet mode analysis is employed to approximate the rest of the absorber lined walls by virtual surfaces with equivalent reflection coefficients. The total quiet-zone field then becomes the superposition of the field radiated by the equivalent currents, and the field scattered by the virtual reflective surfaces. The scattered field is calculated from the SBR method. The required equivalent currents of the throat and the reflection coefficients of absorber array walls are computed with the use of the FEM, which allows the considerations of the complex structure and near-field interaction. Numerical examples are presented to demonstrate the feasibility of the proposed method.
Over-the-Air Performance Evaluation of NB-IoT in Reverberation Chamber and Anechoic Chamber
NB-IoT (Narrowband Internet of Things) is a narrowband radio technology showing very different characteristics compared with traditional wireless protocols. For the first time based on authors' best knowledge, this paper compares the Over-the-Air (OTA) performance of NB-IoT in the Reverberation Chamber (RC) and Anechoic Chamber (AC), which involves two major RF test environment variations in the OTA test arena. In this paper, the Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS), related to the transmitter and receiver performance of NB-IoT, respectively, are investigated. For TIS test, an early exit algorithm with 95% confidence level based on Chi-Square distribution has been developed to improve the test speed. The test results show a good match (Within CTIA allowed measurement uncertainty) between AC and RC. Our analysis also includes several key parameters, such as test repeatability, measurement uncertainty, and test time, which gives a comprehensive comparison of different aspects between RC and AC for NB-IoT OTA test. It could be noticed as well that the early exit algorithm based on Chi-Square distribution improves the test time performance significantly without compromising the test accuracy.
Coupling Suppression and Measurements on a Millimeter Wave Cylindrical Repeater
This paper discusses some aspects of isolation improvement and associated measurements on a cylindrical millimeter-wave repeater operating over K, Ka and V bands. The isolation between the transmitting and receiving antennas is improved by means of reactive impedance surface implemented as tapered depth corrugations. The designed tapered depth profile broadens bandwidth of the surface compared to the traditional quarter wavelength corrugations. Required isolation of 80 dB and large electrical size of the platform make numerical analysis and actual measurements challenging. Details of the analysis and measurements are summarized. Along with external coupling, the coupling due to leakages from waveguide components and antennas is also discussed. Measurements confirm that the design goal isolation is accomplished.
Implementation of a Technique for Computing Antenna System Noise Temperature Using Planar Near-Field Data
This paper presents the second phase of the development of a new measurement technique to determine antenna system noise temperature using data acquired from a planar near-field measurement. In the first phase, it was shown that the noise temperature can be obtained using the plane-wave spectrum of the planar near-field data and focusing on the portion of the spectrum in the evanescent region or "imaginary space". Actual evanescent modes are highly attenuated in the latter region and therefore the spectrum in this region must be produced by "errors" in the measured data. Some error sources such as multiple reflections will produce distinct localized lobes in the evanescent region and these are recognized and correctly identified by using a data point spacing of less than /2 to avoid aliasing errors in the far-field pattern. It has been observed that the plane wave spectrum beyond these localized lobes becomes random with a uniform average power. This region of the spectrum must be produced by random noise in the near-field data that is produced by all sources of thermal noise in the electronics and radiated noise sources received by the antenna. By analysing and calibrating this portion of the spectrum in the evanescent region the near-field noise power can be deduced and the corresponding noise temperature determined. In the current phase of tests, planar near-field data has been acquired on a measurement system and the analysis applied to determine the system noise parameters. Measurements have been performed with terminations inserted at three different locations in the RF receiving path: the IF input to the receiver, the input to the mixer and the input to the probe that is transmitting to a centre-fed reflector antenna. The terminations consist of either a load that serves as the "cold" noise source or a noise source with a known noise output for the "hot" noise source.
Optimized Compact Antenna Test Range with Short Focal Length for Measuring Large L/Ku-Band Active Antennas
A new Compact Antenna Test Range (CATR) has been built, as a turnkey facility, with a cubic quiet zone (QZ) of 4.8m x 4.8m x 4.8m in the frequency range 0.9-18 GHz. The CATR has been installed in a new building with an isolated and stable foundation. The dimensions of a traditional CATR for such QZ size becomes impractical and requires a very large chamber. A new, diagonally fed, short focal length reflector has been developed to minimize the chamber size to fit the dimensions of 22 m x 14.5 m x 14.5 m.
Reference Chip Antenna for 5G Measurement Facilities at mm-Wave
In this paper, we present a chip antenna in the 27GHz band, targeting 5G measurements. This antenna can be used as reference in mm-wave measurement systems, such as the MVG µ-Lab, feeding the antenna under test through a micro-probe station. The reference antenna is employed to calibrate in gain through the substitution method. The antenna shown in this paper is an array of four patches, fed through a strip-line beam forming network. A transition strip-line to coplanar waveguide allows the antenna be fed by the micro-probe.
Near Field Reconstruction for Electromagnetic Exposure of 5G Communication Devices
Compliance with regulatory exposure requirements of power density for 5G systems will need accurate measurements. In this work a near field measurement technique for electromagnetic exposure of 5G communication devices is presented. The technique requires two measurements, one of a device under test and one of a small aperture as a calibration measurement. The method uses method of moments and involves reconstructing equivalent currents on a predefined surface. These currents are then used to generate and propagate the electromagnetic fields to an arbitrary plane and further compute the power density. The measurement data are obtained through a planar scan of a device under test using a probe and probe calibration using a small aperture to obtain an accurate field with absolute positioning. Measurement data is presented and compared with simulations for several distances and two antennas, operating at 28 GHz and 60 GHz. The computed power density agrees well with simulations.
Imaging a Range's Stray Signals with a Planar Scanner
The fundamental purpose of absorber treatment in an anechoic chamber is to ensure that only the direct-path signal is coupled between the range antenna(s) and the device under test. For many simple and standard geometries, this is readily accomplished with conventional processes and procedures. When the geometry and/or stray-signal requirements deviate from the norm, however, it can be very beneficial to have an easy and reliable way to locate and quantify sources of stray signals. This paper discusses a straightforward algorithm for creating images of those stray signals in a range when a planar scanner and broad-beamed probe are available in the test zone. Measured data from multiple facilities are evaluated, along with absorber-treatment improvements made based on some of the images produced.
Indoor Antenna Measurement Facility: Determination of the phase center position
Indoor antenna measurement facilities are usually dedicated to characterize all the parameters of an antenna. In order to perform phase center position measurements, the CEA has designed a specific experimental layout to characterize this parameter with a very high accuracy. This paper describes this measurement facility and deals with technical decisions made during its design phase. Finally, we will talk about possibilities offered by this specific layout and the advantages of this layout compared to a classical antenna test-bench.
Antenna Modeling on Complex Platforms Through Constrained Equivalent Aperture Distributions
Accurate in situ antenna manifolds are desired for performance evaluation of radio frequency systems, including communication, navigation, and radar among others. In situ antenna measurements are the most accurate way to obtain antenna manifolds on the platform of interest, but are often impractical or impossible to obtain. Instead, combinations of simulations and measurements are used to estimate antenna manifolds on platforms. First, the gain and phase of the target antenna are measured on a simple ground plane, over the frequencies and field of view of interest. The measurements are then imported into computational electromagnetics codes to simulate platform scattering from the platform of interest. However, the representation of the measured data is not unique, which leads to inaccuracies and/or a large run time in computational electromagnetics codes. This paper presents a new method to represent measured antenna data in electromagnetics codes through aperture current distributions of simulated cross-slots and monopoles. A weighted sum of far-fields from the simulated equivalent elements approximates the measured antenna far-fields, with weights determined by the minimization of the L2-norm difference between measured far-fields and equivalent element far-fields. However, the least square solution may place large, unrealizable currents on the aperture. A constraint is introduced to limit the amount of current on the aperture, by minimizing the length of the solution vector. In this paper, the details of the suggested method will be presented. We will also illustrate the accuracy of the method through example simulations, where good agreement is achieved between truth data and equivalent antennas on complex platforms.
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