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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.
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.
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.
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.
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.
The Low frequency Coaxial Reflectometer is the recommended procedure to measure the absorbers' reflectivity as per the IEEE 1128-1998 standard. The standard recommends the operable frequency range up to 500 MHz with a permissible error of 2 dB and higher error beyond 600 MHz. This paper studies and discusses the error on different types of absorber. Each of the absorber type is simulated in the square section of the reflectometer setup to compute the absorber's reflectivity using Ansys HFSS. An effective time gating technique is applied to reduce the effect of edge effects. These results are compared to the unit cell simulation results with a plane wave excitation and periodic boundary conditions. The absorbers are then simulated in the complete reflectometer setup to include the mismatch associated with the transition and compared to the unit cell model results. The errors associated with the comparison of the absorbers' simulation results for these different models are analyzed. The combination of these different absorbers is simulated in unit cell model. The absorbers are placed in different regions and orientations inside the reflectometer. The comparison between the unit cell results of the combination of the absorbers and the results of the absorbers inside the reflectometer in different orientations give the effect of the non-uniform field distribution inside the reflectometer.
The need for thermal stability in a test chamber is a well-established requirement to maintain the accuracy and repeatability sought for high frequency planar near-field (PNF) scanner measurements. When whole chamber thermal control is impractical or unreliable, there are few established methods for maintaining necessary precision over a wide temperature range. Often the antenna under test (AUT) itself will require a closed-loop thermal control system for maintaining stable performance due to combined effects from transmission heat dissipation and the environment. In this paper, we propose a new approach for near-field system design that leverages this AUT stability, while relaxing the requirement of strict whole chamber thermal control. Fixed reference monuments strategically placed around the AUT aperture perimeter, when measured periodically with a sensing probe on the scanner, allow for the modeling and correction of the scanner positioning errors. This process takes advantage of the assumed stability of the reference monuments and attributes all apparent monument position changes to distortions in the scanner structure. When this monument measurement process is coupled with a scanner structure that can tolerate wide thermal variations, using expansion joints and kinematic connections, a robust structural error correction model can be generated using a bilinear mapping function. Application of such a structure correction technique can achieve probe positioning performance similar to scanners that require tightly controlled environments. Preliminary results as well as a discussion on potential design variations are presented.
Prior literature in the subject area of far-field antenna measurements has demonstrated an extrapolation technique to isolate and correct the errors due to near-zone proximity effects as well as multi-path range reflections, thus allowing data to be collected at distances much less than the conventionally defined far-field criteria. This paper describes a modern, indoor, far-field antenna measurement range specifically designed to support this extrapolation technique. A multi-axis positioning system featuring a mobile horn tower capable of motion along the chamber Z-axis is emphasized. High-speed RF instrumentation and advanced software control support the full automation of the extrapolation method. This contemporary approach is demonstrated, and measurement examples are provided for an X-band slotted waveguide array. The resultant far-field gain calculations are also compared to similar data extracted using near-field scanning techniques.
An ambitious resurfacing campaign was launched in late 2017 to correct for large reflector surface distortions present at the NASA LaRC Experiment Test Range (ETR) in support of performing Europa Clipper flight High Gain Antenna (HGA) measurements at X-and Ka-band frequencies. The effort was successful as the worst case peak-to-peak amplitude ripple was reduced from 4.0-dB to 1.5-dB across the 4.1-meter quiet zone.
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.
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.
This paper presents a new measurement method based on the parallel plate capacitor concept, which determines complex permittivity of dielectric sheets and films with thicknesses up to about 3.5 mm. Unlike the conventional devices, this new method uses a greatly simplified calibration procedure and is capable of measuring at frequencies from 10 MHz to 2 GHz, and in some cases up to 6 GHz. It solves the parasitic impedance limitations in conventional capacitor methods by explicitly modeling the fixture with a full-wave computational electromagnetic code. Specifically, a finite difference time domain (FDTD) code was used to not only design the fixture, but to create a database-based inversion algorithm. The inversion algorithm converts measured fixture reflection (S11) into dielectric properties of the specimen under test. This paper provides details of the fixture design and inversion method. Finally, example measurements are shown to demonstrate the utility of the method on typical microwave substrates.
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 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.
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.
Time and Direction of Arrival (TADOA) analysis of field probe data has been an accepted method for characterizing stray signals in an antenna measurement range for many years ([1], [2]). Recent uncertainty investigations at the OneRY range have shown a need for increased resolution to isolate and characterize energy in TADOA images so that resources can be carefully applied to reduce the uncertainty from these stray signals. This is accomplished by modeling the TADAO image as the solution to a Basis Pursuit (BP) l1 minimization problem. This paper outlines the model development and shows concrete examples from OneRY field probe data where BP allows for the identification of stray energy which was previously difficult to find. We also show how the BP optimization context can be using to remove contamination from the data through the inclusion of additional basis functions ([3]). I.J. Gupta, E.K. Walton, W.D. Burnside, “Time and Direction of Arrival Estimation of Stray Signals in a RCS/Antenna Range,” Proc. of 18th Annual Meeting of the Antenna Measurement Techniques Association (AMTA '96), Seattle WA, September 30-October 3, 1996, pp. 411-416. I.J. Gupta, T.D. Moore, “Time Domain Processing of Range Probe Data for Stray Signal Analysis,” Proc. of 21st Annual Meeting of the Antenna Measurement Techniques Association (AMTA '99), Monterey Bay CA, October 4-8, 1999, pp. 213-218. B.E. Fischer, I.J. LaHaie, M.H. Hawks, T. Conn, “On the use of Basis Pursuit and a Forward Operator Dictionary to Separate Specific Background Types from Target RCS Data,” Proc. of 36th Annual Meeting of the Antenna Measurement Techniques Association (AMTA '14), Tucson AZ, October 12-17, 2014, pp. 85-90.
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.
One of the sources of the measurement errors in outdoor antenna test ranges, when testing from VHF through C-Band, is the ground reflected signal between probe antenna and the antenna under test (AUT). Those errors are due to antenna(s) relatively large beam width(s) at these frequencies, especially when AUT is placed on the large platform such as an aircraft. If reflected wave is not eliminated by the use of absorbers at the reflection point or redirection by the use of diffraction fences, then the range operates as a ground reflection range (GRR), where the reflected signal creates a lobbing pattern when the direct and reflected signals are overlaying in- and out-of-phase as a function of position and frequency, causing undesirable amplitude variations at the test point. Ground reflections may be a major cause of error for GRR measurements when testing large antennas or antennas mounted on large structures which require a large displacement of the AUT during the antenna pattern collection process. A concept of using vertically positioned two-element array probe antenna (source antenna) to suppress ground-reflected signals in GRR-s is presented in this article. Suppression is achieved by pointing first null of the probes gain pattern towards the reflection point on the ground. All analytical evaluations are based on geometrical optics approach. Comparison of the proposed approach to a traditional single-element probe (source) antenna approach, demonstrates a significant improvement in measurement accuracy. Estimates and verifications of analytical evaluations are based on Computational Electromagnetics (CEM) modeling tool such as WIPL-D code. Simulations are performed in the VHF frequency band (200 MHz).
Among the near-field – far-field (NF-FF) transformation techniques, the one employing the bi-polar scanning is particularly interesting, since it retains all the advantages of that using the plane-polar one, while requiring a mechanically simple, compact, and cheaper measurement facility [1]. In fact, in this scan, the antenna under test (AUT) rotates axially, while the probe is mounted at the end of an arm that rotates around an axis parallel to the AUT one. An effective probe voltage representation on the scanning plane requiring a minimum number of bi-polar NF data has been developed in [2], by properly exploiting the nonredundant sampling representations of electromagnetic (EM) fields [3] and considering the AUT as enclosed in an oblate ellipsoid. A 2-D optimal sampling interpolation (OSI) formula is then employed to efficiently recover the NF data required by the traditional plane-rectangular NF-FF transformation [4] from the acquired nonredundant bi-polar samples. It is so possible to considerably reduce the number of the needed NF data and corresponding measurement time with respect to the previous approach [1], which did not exploit the nonredundant sampling representations. However, due to an imprecise control of the positioning systems and their finite resolution, it may be impossible to exactly locate the probe at the points fixed by the sampling representation, even though their position can be accurately read by optical devices. Therefore, it is very important to develop an effective algorithm for an accurate and stable reconstruction of the NF data needed by the NF-FF transformation from the acquired irregularly spaced ones. A viable and convenient strategy [5] is to retrieve the uniform samples from the nonuniform ones and then reconstruct the required NF data via an accurate and stable OSI expansion. In this framework, two different approaches have been proposed. The former is based on an iterative technique, which converges only if there is a biunique correspondence associating at each uniform sampling point the nearest nonuniform one, and has been applied in [5] to the uniform samples retrieval in the case of cylindrical and spherical surfaces. The latter, based on the singular value decomposition (SVD) method, does not exhibit this constraint and has been applied to the nonredundant bi-polar [6] scanning technique based on the oblate ellipsoidal modeling. However, it can be conveniently used only when the uniform samples recovery can be split in two independent one-dimensional problems. The goal of this work is not only to provide the experimental validation of the SVD based technique [6], but also to develop the approach using the iterative technique and experimentally assess its effectiveness. [1] L.I. Williams, Y. Rahmat-Samii, R.G. Yaccarino, “The bi-polar planar near-field measurement technique, Part I: implementation and measurement comparisons,” IEEE Trans. Antennas Prop., vol. 42, pp. 184-195, Feb. 1994. [2] F. D’Agostino, C. Gennarelli, G. Riccio, C. Savarese, “Data reduction in the NF-FF transformation with bi-polar scanning,” Microw. Optic. Technol. Lett., vol. 36, pp. 32-36, 2003. [3] O.M. Bucci, C. Gennarelli, C. Savarese, “Representation of electromagnetic fields over arbitrary surfaces by a finite and nonredundant number of samples,” IEEE Trans. Antennas Prop., vol. 46, pp. 351-359, March 1998. [4] E.B. Joy, W.M. Leach, Jr., G.P. Rodrigue, D.T. Paris, “Application of probe-compensated near-field measurements,” IEEE Trans. Antennas Prop., vol. AP-26, pp. 379-389, May 1978. [5] O.M. Bucci, C. Gennarelli, G. Riccio, C. Savarese, “Electromagnetic fields interpolation from nonuniform samples over spherical and cylindrical surfaces,” IEE Proc. Microw. Antennas Prop., vol. 141, pp. 77-84, April 1994. [6]F. Ferrara, C. Gennarelli, M. Iacone, G. Riccio, C. Savarese, “NF–FF transformation with bi-polar scanning from nonuniformly spaced data,” Appl. Comp. Electr. Soc. Jour., vol. 20, pp. 35-42, March 2005.
Modern cars are equipped with a large number of antennas which are strongly integrated with the car. A full characterization of the radiating properties of the entire vehicle is thus typically required. In order to characterize the radiating properties of the installed antennas, large measurement systems accommodating the full vehicle are required. As in standard antenna measurements, a full spherical near field (NF) scanning around the car is desirable in order to perform an accurate NF/FF transformation. However, due to size and weight of the Device Under Test (DUT) and/or economic factors a full spherical scan is often unfeasible. For this reason, truncated spherical scanners (such as hemispherical) are typically involved. A classic solution is to combine hemispherical scanning with a metallic ground plane which is assumed to be a Perfect Electric Conductor (PEC) in the NF/FF transformation. However, the PEC ground-plane is less representative of realistic automotive environments such as asphalt that is strongly dielectric. A further drawback is the strong scattering from the large metallic ground-plane which highly compromises the NF measurements at low frequencies. In many situations, it is thus desirable to perform the NF measurements in a condition similar to free-space by using absorber materials on the floor. It is well-known that standard NF/FF transformations applied to partial spherical acquisitions generates the so called truncation errors. Such errors are stronger at lower frequencies due to the lower number of spherical modes for fixed DUT size. Moreover, typical antennas for automotive applications are generally low directive thus, the impact of the truncation on the measured pattern is often non-negligible. In such cases advanced post-processing techniques must be involved to mitigate the effect of the truncation errors. In this paper two truncation error mitigation techniques will be compared when applied to automotive measurements performed in free-space conditions. The first technique is an iterative process which at each iteration applies a modal filtering based on the size of the DUT. The second technique is based on the computation of the equivalent currents of the DUT over an equivalent surface which acts as spatial filter. Both techniques give excellent mitigation performance with different computational effort. The good agreement between two different techniques effectively defining the lower bound for what can be successfully mitigated by post processing techniques.