AMTA Paper Archive
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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.
Multi-Objective Optimization of a Reconfigurable Antenna Using a Closed-Loop Planar Near Field Measurement Technique
Empirical optimization of software reconfigurable antennas having hundreds of degrees of freedom demands rapid measurement, especially when multiple objectives, e.g. gain at multiple angles and polarizations, are included. This paper describes a measurement technique and process flow for rapid optimization of antenna performance. Previously, such evaluation with mechanical scanning was slow and impractical. The technique is enabled by closed-loop automation of an electronically scanned near field measurement system that determines the hemispherical radiation pattern of a given antenna state in approximately 1 second. In this way thousands of antenna states are evaluated per hour. This paper presents measurements of antenna states optimized using the new technique, and results are compared to measurements of states optimized by the usual far field technique.
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.
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.
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.
Top-fed P-band Dual Circular Polarization Patch Antenna Design
This paper discusses about the design, fabrication and testing of a compact P-band (370 MHz) dual circular polarization (CP) patch antenna. The antenna is intended for reflectometry applications by measuring both direct and ground reflected 370 MHz signals transmitted from a satellite or airborne source. This design adopts quadrature-phase hybrid feeding network for achieving excellent polarization purity and supporting simultaneously LHCP and RHCP measurements. Another novel design aspect is placing the feeding network on top of the patch so that the antenna can be mounted directly on a ground plane. Therefore, the resonant modes inside the patch is excited from the top instead of from ground plane as in conventional designs. High dielectric material (ECCOSTOCK®HiK) with a dielectric constant of 9 and loss tangent of 0.002 was used as the substrate to reduce the antenna size. The final antenna has a dimension of 5.9" x 5.9" x 1.3" (excluding ground plane) and weight of 1620 gram. The measured performance on a 1-foot diameter circular ground plane showed 4.5 dBic gain and 23 dB co-polarization to cross-polarization isolation at the center frequency for both LHCP and RHCP. The 1-dB gain bandwidth is approximately 3.7%.
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.
Evaluation of Software Defined Radio Receiver for Phaseless Near-Field Measurements
This paper presents a time domain antenna measurement technique by using a low cost software defined radio receiver. The technique aims to resolve measurement challenges derived from antennas where the reference signal is not accessible. The phase reconstruction implemented in this work is based on calculating the Fast Fourier Transform of the time domain signal to estimate the power spectrum and the relative phase between measurement points. In order to do that a reference antenna is used to retrieve the phase, providing a full characterization in amplitude and phase of the electric field and allowing source reconstruction. The results demonstrate the potential of this technique for new antenna measurement systems and reveal some of the limitations of the technique to be optimized, like the undesired reflections due to the interactions between the probe and the reference antenna.
Laboratory Proofs on a Nonredundant Spherical NF-FF Transformation for a Quasi-Planar AUT Mounted in Offset Configuration
This communication provides an experimental assessment of an accurate near-field-far-field (NF-FF) transformation with spherical scan, properly developed to take into account a mounting in offset configuration of a quasi-planar antenna under test (AUT). Such a technique relies on the nonredundant sampling representation of electromagnetic fields and, unlike the classical NF-FF transformation, it allows the reconstruction of the far field radiated by an AUT from a minimum number of NF data, which remains practically the same both when the AUT is mounted in onset and offset configuration, since this number is related only to the surface modeling the AUT. Such a surface has been here chosen coincident with that formed by two circular bowls with the same aperture and eventually different bending radii. Experimental results assessing the validity of such a technique are reported.
Application of Complex Image Theory for Nearfield Antenna Measurements over Seawater
The principles of near-field antenna measurements in Cartesian, cylindrical, and spherical coordinates are well established and documented in the literature and in standards used on antenna ranges throughout government, industry, and academia. 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 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. In this paper, we shall discuss a possible avenue for addressing this problem : the use of Complex Image Theory (CIT). The CIT approach allows the lossy earth to be removed and an image of each equivalent source point in the space above it to be constructed in the now empty space below it, but where the depth of that image is in general a complex number. While it might appear confusing to define a complex depth, such a depth is merely a mathematical construct that accounts for a magnitude and phase shift that occurs due to the presence of the lossy ground. The depth is computed so that the boundary condition at the surface of the original lossy ground is maintained; in this way, an equivalent problem is formulated. We propose an approach based on CIT that can be applied to the problem of a spherical nearfield antenna measurement taken over seawater. A limiting case of measurements taken over a metal ground plane shall be presented, along with thoughts about some practical concerns involved in the performance of such measurements.
Measurement Methodology For Fast Antenna Testing Using Existing PNF ranges
In this paper, we investigate the achievable time savings in planar near-field (PNF) measurement of high gain antennas using a planar wide-mesh scanning (PWMS) approach [1-2]. The PWMS employs at least four times less measurements points than standard scanning without degrading the measurement accuracy leading to an under-sampling factor of four. Such mesh scanning can be implemented on standard planar near-field systems similar to the ESTEC, Hertz PNF scanner [3, 4]. The measurement accuracy vs time-saving for the wide-mesh approach is investigated using the numerical model of a highly-shaped Ku-band reflector antenna. This antenna is a realistic representation of what is currently flying on typical satellites with European coverage such as Eutelsat W . The Near Field to Far Field transformation accuracy is investigated by comparing traditional and PWMS results using the same base data from the antenna model. A discussion on implementation on existing scanners and the relation with measurement time-savings is included. The experimental verification of the technique will be included in the conference presentation.
Uncertainty Analysis Technique for Planar Field-Probing Measurements and Quiet-Zone Simulations of a Compact Antenna Test Range
The performance of a compact antenna test range is evaluated by field-probing measurements of the quiet zone. The comparison between the simulated and measured data, however, is misleading due to the finite measurement accuracy and the limited nature of the numerical model. In order to allow a comparison, the uncertainty terms of the field-probing measurements and the numerical model are identified based on the National Institute of Standards and Technology 18-term uncertainty analysis technique. The individual terms are evaluated with simulations or measurements using the equivalent-stray-signal model. Bearing the differences between the model and the actual measurements in mind, the electrical field can be estimated precisely within the overlapping region of both uncertainty budgets.
A Novel GO-PSO Algorithm for Designing 3D- Printed Optimized Pixelized Inhomogenous and Shaped-Profiled Lens Antennas
In this paper, a novel algorithm for designing 3D-printed shaped inhomogeneous dielectric lens antennas is provided. The synthesis approach is based on a novel combination of Geometrical Optics (GO) and the Particle Swarm Optimization (PSO) method. The GO method can trace rays through inhomogeneous media and calculate the amplitude, phase, and polarization of the electric field. The algorithm is used to design an inhomogeneous lens antenna to produce an electronically scanned revolving conical beam to replace a mechanically scanned parabolic reflector antenna for spaceborne weather radar satellite antenna applications. Two breadboard model on-axis fed lens designs are presented and measured results given to validate the approach. A representative optimum off-axis design is presented which produces the revolving conically scanned beam. Imposition of a Body-of-Revolution restriction allows the optimization to be performed at a single offset feed location. The complex inhomogeneous engineered materials that results from optimization are printed using new 3D printers.
Measurements of the dynamic pattern of an electronically steerable phased antenna array with circular polarization in Ka-band
This paper presents two methods for measuring dynamic antenna patterns of phased arrays in a compensated compact range. The first method uses the turntable of the compact range to counter steer the antenna beam. The dynamic pattern is created by measuring single points of the pattern over time. This method is successfully tested, and the measurement results show the effect of phase jumps during the steering process. The second method extends the range of application to fast steering phased arrays by decoupling the antenna scan angle and the azimuth angle of the turntable.
A Procedure to Characterize and Predict Active Phased Array Antenna Radiation Patterns from Planar Near-Field Measurements
This contribution details a procedure to collect and process necessary data to describe the antenna patterns of PAAs using a planar near-field (NF) range. It is proposed that a complete characterization methodology involves not only capturing beam-steered antenna patterns, but also measuring embedded element patterns, exhaustive testing of the excitation hardware of the antenna under test (AUT), and performing a phased array calibration technique. Moreover, to demonstrate the feasibility of the proposed approach, the methodology is applied onto a 2x8 microstrip patch PAA, proving its utility and effectiveness. Finally, by means of the collected data, any array pattern could be predicted by post-processing, as proven by the great agreement found between a measured pattern and its computed predicted version.
An Efficient Approach to Recover the Nonredundant Plane-Rectangular NF Data from the Inaccurately Probe Positioned Ones
An efficient technique, which allows the correction of known positioning errors in a near-field to far-field (NF-FF) transformation with planar wide-mesh scanning (PWMS), is here developed and experimentally assessed. The corresponding NF-FF transformation from correctly positioned samples allows a remarkable reduction of the acquisition time with respect to the classical plane-rectangular one, since the NF data needed by this last are accurately recovered from a reduced number of PWMS samples through a 2-D optimal sampling interpolation expansion, attained by modeling the antenna under test with a double bowl and applying the nonredun-dant sampling representations to the voltage detected by the scanning probe. When the PWMS samples are affected by known probe positioning error, the voltage values at the sampling points, set by the representation, are unknown and can be efficiently retrieved from the inaccurately positioned ones by means of a singular value decomposition based technique.
Multi-Level Spherical Wave Expansion for Fast Near- Field to Far-Field Transformation
Traditional near-field to far-field transformation algorithms based on modal expansion are unable to deal with arbitrary measurement surfaces. To approach these problems, a matrix inversion method can be used to retrieve the spherical wave expansion (SWE) of the antenna under test (AUT) fields. Modeling the antenna with a set of multiple SWEs centered at arbitrary points over its surface offers a flexible approach for the solution of field transformation problems over arbitrary surfaces. The coefficients of each SWE are obtained using an iterative inversion approach where the matrix-vector products can be replaced by multilevel operators based on recursive aggregations and interpolations of the partial SWE fields, reducing the computational complexity from í µí± ¶(í µí² í µí¿) to í µí± ¶í µí² í µí¿ í µí°¥í µí°¨í µí° í µí². The proposed algorithm is tested using synthetic data and measurements showing good scalability and reduced transformation error.
Adding Phase to the Rotating-Source Antenna Polarization Measurement Method
The rotating-source measurement method is usually described as an amplitude only measurement method and the axial ratio is the only characteristic that can be measured. The article illustrates how adding a phase measurement allows to get the sense of polarization and to calculate the circular partial gains over a full cut-plane of the antenna under test. Simulations and a measurement example are shown.
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