Dipole-Field Simulations: Evaluation of NIST Spherical Near-Field Software
We use a simple program to compute fields radiated by a collection of elementary electromagnetic dipoles located at arbitrary points within the measurement sphere. The simulated measurement data have been used to provide a direct and convincing demonstration of the accuracy and robustness of both the standard and position compensated NIST SNF code.
Eliminate Celestial Noise Sources in Your SatCom G/T Measurements
The current method of measuring system G/T performance is with the use of celestial noise sources (sun and cold sky). This paper details a method using man-made noise sources to measure system performance within an anechoic chamber, followed by an outdoor measurement to obtain G/T performance in a real world operational environment. A simple method is presented and equations derived that relate system performance in unknown environments to performance with known noise sources.
Reducing the Scanning Time in Near-Field Measurements with an Optimized Sampling and an Optimized Controller on Arduino Due
The aim of the paper is to address a relevant issue in the Near-Field (NF) measurements: the reduction of the measurement time. Generally speaking, for a given hardware, two main directions can be pursued. The first requires the adoption of an optimal field sampling strategy that reduces the number of sampling points, and the length of the scanning path, without impairing accuracy. The second strategy adopts an optimized control system able to exploit at the best the available hardware (scanning system and measurement instrument). Indeed, the latency of the instrument defines the maximum probe velocity during the field acquisition. Accordingly, unlike the conventional continuous scanning, an optimized controller can speed up the scanning by moving the probe along the measurement trajectory with a variable velocity, accelerating and decelerating between two consecutive sampling points, to increase the average speed. However, the use of an optimized controller is fruitful only when the optimized sampling scheme allows large distances between two consecutive sampling locations, to increase as much as possible the maximum probe speed. In this paper, by suitably using both the above strategies, it is proposed a fast NF system, implemented on a microcontroller Arduino Due, an extremely cheap and off the shelf hardware, that is able to handle the scanner and realize the synergy between the optimized sampling and the optimized control strategy. The simulation and experimental results show a dramatic reduction of the measurement time (up to one order of magnitude) with a high tracking precision (also in accordance with the proposed methodology), and of the costs with respect to standard solutions.
Using Standard Wideband Antennas as Probe in Spherical Near Field Measurements with Full Probe Correction: Experimental Validation
Full probe compensation techniques for Spherical Near Field (SNF) measurements have recently been proposed [1-5]. With such techniques, even antennas with more than decade bandwidth are suitable probes in most systems. The abolition of otherwise frequent probe changes during multi-service campaigns is a highly desirable feature for modern measurement applications such as automotive. In this paper, a standard dual-ridge horn with 15:1 bandwidth is investigated experimentally as probe in a SNF automotive range. The accuracy of the probe compensation technique is validated by comparison to standard single probe measurement.
Asymptotic Simulation Methods in Anechoic Chamber Design
When designing an anechoic chamber, determination of the extent and quality of the quiet zone is crucial. While rigorous simulation methods can be used for this in principle, in practice such methods quickly become too computationally expensive with increasing frequency. In this paper, the authors evaluate a couple of asymptotic approaches based on ray tracing, and quantify their value for anechoic-chamber design.
A Compressed Sampling for Spherical Near-Field Measurements
Spherical near-field measurements are regarded as the most accurate technique for the characterization of an Antenna Under Tests (AUT) radiation. The AUT's far-field radiation characteristics can be calculated from the Spherical Mode Coefficients (SMC), or spherical wave coefficients, determined from near-field data. The disadvantage of this technique is that, for the calculation of the SMC, a whole sphere containing the AUT must be Nyquist-sampled, thus directly implying a longer measurement time when only a few cuts are of interest. Due to antennas being spatially band-limited, they can be described with a finite number of SMC. Besides, the vector containing the SMC can be proved sparse under certain circumstances, e.g., if the AUT's radiation pattern presents information redundancy, such as an electrical symmetry with respect to coordinate system of the measurement. In this paper, a novel sampling strategy is proposed and is combined with compressed-sensing techniques, such as basis pursuit solvers, to retrieve the sparse SMC. The retrieved sparse SMC are then used to obtain the AUT's far-field radiation. The resulting far-field pattern is compared for both simulated and measured data. The reduced number of points needed for the presented sampling scheme is compared with classical equiangular sampling, together with the estimated acquisition time. The proposed sampling scheme improves the acquisition time with a reasonable error.
Near-Field Spherical Scanning Measurement of a 3D Printed Horn at WR-8 Frequencies
The National Institute of Standards and Technology (NIST) has measured a WR-8, 3D printed horn at 112.25, 118.75, and 125.25 GHz using the near-field spherical scanning method. The data were processed with both the NIST standard software and the probe-position compensation software. We conclude that the positioning capability of the NIST Configurable Robotic Millimeter-wave Antenna System is so accurate that probe-position compensation is negligible at these frequencies.
Low-Cost Pressure/Temperature Measurements of Wideband Antennas
This paper discusses design and fabrication of a low cost, combined pressure / thermal test-bench engineered for environmental tests of UAV mounted antennas. Both test-beds are mainly made of commercial of-the-shelf (COTS) parts and in-house made frames. They occupy small space and do not require specific professional skills for operation or high maintenance cost. Measurement setup is designed to reliably reproduce temperature and pressure corresponding to altitudes from sea level to 6000 m (20000 ft) with dynamic load equivalent for 200 m/s (400 knots) of air speed. Experimental results of radome enclosed wideband antenna are presented.
Spherical Phaseless Probe-Corrected Near-Field Measurements of the DTU-ESA VAST12 Reflector Antenna
An experimental case of spherical probe-corrected phaseless near-field measurements with the two-scans technique is presented, based on magnitude measurements at two surfaces of the VAST12 reflector antenna performed at the DTU-ESA Facility. Phase retrieval using strictly the directly measured near-field magnitude was unfeasible in this setup, due to the small sphere separation allowed by the probe positioner, which led to incorrect and excessively slow convergence. Phase retrieval with larger separation between spheres has shown remarkable results. For these tests a measured magnitude was used in combination with calculated near-field magnitudes at different (larger and smaller) spheres with larger separations than allowed by the experimental setup. It has been seen that larger separation between measurement spheres improves accuracy of phase retrieval. A measurement with a backprojected measurement with 3 m sphere separation is of particular interest because it can be potentially replicated in the DTU-ESA Facility assuming such range of movement was allowed, while being accurate down to an error of less than-35dB. Measurements with larger spheres show even better accuracy. These good results were obtained with the normal spatial sampling rate for complex measurements and with a very simple Hertzian dipole initial guess, and show the superior performance of spherical phaseless measurements with the two-scans technique, compared to a planar setup.
Automotive MIMO Cellular Antenna Performance Comparison in an Over-The-Air Environment
This paper addresses the MIMO performance of automotive cellular antenna configurations as measured in an OTA (Over-The-Air) chamber. The OTA chamber measurement has been adopted by the cellular communications industry as a way to validate wireless devices such as smartphones, tablets and modems for RF compliance to the Carrier's network requirements. This performance assessment of an automotive cellular antenna in an OTA chamber is an approach to compare to wireless device performance and antenna verses antenna. The parameters that will be compared as a result of the OTA measurements are TRP (Total Radiated Power), TIS (Total Isotropic Sensitivity) and Data Throughput for given signal levels.
A New Formulation for Three Antenna Polarization Measurements
In this contribution the signal received by an antenna is understood as an inner product built by the polarization vectors of the involved antennas. By using a suitable unitary transformation the polarization efficiency can be straightforwardly calculated without additional assumptions. By solving an eigenvalue problem given by a unitary operator which represents a rotation, a simple and illustrative interpretation is possible. The formulation is applied to derive the well-known relations of the improved three antenna polarization measurement technique given by Allen C. Newell, which is mainly based on the measurement of relative power levels. Some measurement results and the calculation of the achievable measurement accuracy are presented.
Rydberg Atom-based RF Power Measurements
The power transmitted through a waveguide was determined using in-situ atom-based electric field measurements. The field distribution in the waveguide was measured using Rydberg atoms to find the maximum field, which was used to determine the power. For a proof-of-concept, the power of radio frequency fields at 17.86, 19.63, 26.53, and 33.03 GHz were measured in a WR42 waveguide. A section of waveguide was sealed and filled with cesium atoms. These atom-based measurements are self-calibrated and independent of typical power measurement methods.
Parameter Extraction Algorithm for Conductor Backed, Bi-Layered Uniaxial Materials
An algorithm is developed for the extraction of constitutive parameters from bi-layered uniaxial anisotropic materials backed by a conductive layer. A method of moments-based approach is used in conjunction with a previously-determined Green function. Possible challenges related to measurement diversity are highlighted and a possible mitigation path is proposed.
Equivalent Sources Based Near-Field Far-Field Transformation Above Dielectric Half Space
In order to support near-field measurements of automobile antennas in as realistic as possible environments, an equivalent sources based near-field far-field transformation approach for near-field measurements above a possibly lossy dielectric half-space is presented and evaluated. Different possibilities for considering the half-space influence are discussed, where an approach with an appropriate half-space Green's function is found to be most accurate, as expected. The formulation of the equivalent sources transformation approach with the half-space Green's function and a formulation with free-space Green's function together with equivalent sources representation of the half-space influence are discussed and a variety of results are presented in order to corroborate the feasibility of the various approaches.
Reflection-Based Inverse Scattering Image Reconstruction for Non-Destructive Testing
Non-destructive testing (NDT) is a fundamental step in the production chain of aircraft structural components since it can save both money and time in product evaluation and troubleshooting. This paper presents a reflection-based imaging technique for electromagnetic (EM) testing of composite panels, with the device under test (DUT) being metal backed and both the transmitting and receiving components of the NDT system situated on the same side of the DUT. One of the key properties of the presented technique is the complete redundancy of a reference measurement, thereby making it feasible to retrieve a high quality image of the DUT with only a single measurement. Data for both a proof-of-concept DUT and an industrially manufactured composite panel is provided, and the retrieved images show the applicability of both the measurement technique and the imaging algorithms.
A General and Effective Mode Filtering Method for the Suppression of Clutter in Far-Field Antenna Measurements
The use of mode filtering to improve the quality of antenna measurements taken in non-anechoic environments is well known, [1, 2, 3, 4, 5]. In the far-field case [6, 7, 8], it has been shown that it is possible to use standard cylindrical near-field theory  to implement the necessary mode filtering using a singularly polarized, great circle, far-field pattern cut consisting of amplitude and phase data. The careful verification of this technique using a compact antenna test range (CATR) was reported in [7, 8] however that implementation had, as a prerequisite, the need to acquire the far-field data on a monotonic and equally spaced pattern abscissa. In many instances this is not convenient or perhaps impossible. This paper presents a recent development which allows data to be processed rigorously when having been acquired using an unequally spaced angular abscissa. This paper sets out the novel, far more sophisticated, algorithm together with results of actual range measurements that were processed using this new technique.
Fully Probe Corrected Spherical Near Field Offset Measurements with Minimum Sampling Using the Translated-SWE Algorithm
The Translated Spherical Wave Expansion (TSWE) has recently been proposed as a very effective Near-Field-to-Far-Field (NF/FF) transformation tool for down-sampled Spherical Near Field (SNF) measurements with offset Antenna Under Test (AUT). In case of electrically small probes and/or small AUT-probe view angles the TSWE can be accurately applied without compensating for the probe effect. Instead, when electrically larger probes and/or larger view angles are considered, the measured signal is affected by an averaging field effect that should be properly compensated to ensure a good accuracy. In this paper the TSWE technique is applied for the first time tacking into account the full effect of the measuring probe. To validate the proposed technique, a standard gain horn intentionally displaced in offset configuration have been measured in SNF geometry with a first order probe and two different wideband higher-order antennas as probe.
Plane Wave Generator for Direct Far-field Over-The-Air Testing of Devices
The Plane Wave Generator (PWG) is an array of elements with suitably optimized complex coefficients, generating a plane wave in the close proximity of the array. Thus, the PWG achieve far-field testing conditions in a Quiet Zone (QZ) at a reduced distance in a manner similar to what is achieved in a Compact Antenna Test Range (CATR) . In this paper, the concept of a high performance, dual polarized PWG supporting up to 10:1 bandwidth is presented for the first time. A prototype of a dual polarized PWG has been designed, manufactured and tested in the 600MHz to 6GHz frequency range. The initial testing results on QZ uniformity and evaluation of possible measurement accuracy are presented.
Some Advantages of Using Bi-directional S-Parameters in Near-Field Measurements 1
The unknown-thru calibration technique is being used to achieve a system level calibration at millimeter wave frequencies (>50 GHz) on the robotic ranges at NIST. This two-port calibration requires the use of a full bi-directional measurement, instead of a traditional single-direction antenna measurement. We explored the value of the additional data acquired. We find that we can use this information to verify antenna/scan alignment, image the scattering from the positioner/facility, and perform a first order correction to the transmission data for uncertainties due to LO cable flexure.
Systematic Study: Channel Sounding via Modal Expansion
We present a preliminary study of a modal (partial wave) expansion of the field used to characterize a propagation channel. We assume that the measurements of the scalar, two-dimensional field from which the modal expansion coefficients are obtained, contain Gaussian phase noise with zero mean. Three spatial sampling patterns of the field are considered. We find that the accuracy of the reconstructed field is strongly influenced by the spatial sampling pattern.