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The automotive industry is changing rapidly through the evolution of on board and embedded components and systems. Many of these systems rely on the over the air performance of a communication link and the evaluation of these links is a key requirement in understanding both the real world performance, and associated operating limits of a particular system. The operating frequency range of the installed communication systems now extends from the traditional AM bands from 540KHz to almost 6GHz for WiFi. There are several different antenna design options available to cover this range and in many cases, the performance of an antenna when installed on a vehicle differs from a measurement of the same antenna in isolation. There is also a growing use of high frequency RADAR systems operating at frequencies approaching 80GHz that also need to be included in the performance analysis. The behavior of the individual components using conducted methods for example, is an important step but the direct measurement of antenna pattern and data throughput under ideal steady state and also varying spatial and operating conditions is likely to be the most robust method of channel evaluation. There is a steady march toward vehicle autonomy that is pushing the development of increasingly complex and sophisticated sensors, receivers, transmitters and firmware, all installed on an already well populated platform. The interoperability and EMC performance of these embedded systems is an extension to the need for a fundamental understanding of performance. This paper will present some of the available measurement and evaluation options that could be used as part of an integrated test environment which takes advantages of a number of established techniques.
RCS and Antenna measurement accuracy critically depends on the quality of the incident field. Both compact and far field ranges can suffer from a variety of contaminating factors including phenomena such as atmospheric perturbation, clutter, multi-path, as well as Radio Frequency Interference (RFI). Each of these can play a role in distorting the incident field from the ideal plane wave necessary for an accurate measurement. Methods exist to mitigate or at least estimate the measurement uncertainty caused by these effects. However, many of these methods rely on knowledge of the incident field amplitude and phase over the test region. Traditionally the incident field quality is measured directly using an electromagnetic probe antenna which is scanned through the test region. Alternately, a scattering object such as a sphere or corner reflector is used and the scattered field measured as the object is moved through the field. In both cases the probe/scatterer must be mounted on a structure to move and report the position in the field. This support structure itself acts as a moving clutter source that perturbs the incident field being measured. Researchers at the Air Force Institute of Technology (AFIT) have recently investigated a concept that aims to eliminate this clutter source entirely. The idea is to leverage the advances in drone technology to create a free flying field probe that doesn’t require any support structure. We explore this concept in our paper, detailing the design, hardware, and software developments required to perform a concept demonstration measurement in AFIT’s RCS measurement facility. Measured data from several characterization tests will be presented to validate the method. The analysis will include an estimate of the applicability of the technique to a large outdoor RCS measurement facility.
The radiated efficiency is a key performance indicator for multi-standards frequency agile electrically small antennas (ESA) that are mounted on wireless IoT sensors. One of the techniques to estimate it, consists to integrate, over all the angular directions, the gain measured in the far field condition. The gain-comparison method is usually implemented in the CEA LETI testbench ; which requires an accurate knowledge of the standard horn gain. The introduction of a new RF-optical link to remove coaxial cable perturbation on ESA radiation, in our test bench has raised the opportunity to proceed to an error budget analysis. This paper delivers the main results of this study where the impact of several parameters such as the optical fiber movement, the horn position, the received power level, chamber imperfection… have been evaluated. We have carried on the three antennas method (one Vivaldi and two TEM standard horns) to estimate the complex transfer function of the three antennas. The overall goal is to estimate the detailed uncertainty analysis of the ESA efficiency measurement over a large band of frequencies. This work aims to identify the most impacting effects on uncertainty and to initiate the discussion with the AMTA community how to decrease them.
Current and future beam-steerable phased array antennas require broadband frequency range, multiple-beam operation and fast switching speeds. Near-field antenna testing is an efficient tool to rapidly and securely test antenna array performance, but many of the features of current and next-generation electronically steerable antennas require advances in near-field techniques so as to fully characterize and optimize advanced antenna arrays. For example, system requirements often dictate broadband frequency operation, which presents challenges in terms of probe antenna choices and probe-to-test antenna distances to properly characterize and optimize test antennas with a minimal number of scans and thus satisfy stringent customer requirements in a cost- and time-effective manner. Raytheon is developing near-field antenna test measurement techniques tailored to measure the radiation patterns of multiple beams over wide frequency ranges, to expand the range of test data collected for antenna optimization and customer review. Key test design considerations faced in developing advanced near field characterization techniques will be presented. Custom software to integrate antenna control with the near field measurement system is necessary to provide enhanced capability of characterizing multiple beams. Specialized data processing and analysis tools are needed to process thousands of datasets collected from a single scan, in a timely manner.
In the late 1990’s, Maloney et al. began investigating the design of highly pixelated apertures whose physical shape and size are optimized using genetic algorithms (GA) and full-wave computational electromagnetic simulation tools (i.e. FDTD) to best meet the required antenna performance specification; i.e. gain, bandwidth, polarization, pattern, etc. [1-3]. Visual inspection of the optimal designs showed that the metallic pixels formed many connected and disconnected fragments. Hence, they coined the term Fragmented Aperture Antennas for this new class of antennas. A detailed description of the Georgia Tech design approach is disclosed in [4]. Since then, other research groups have been successfully designing fragmented aperture antennas for other applications, see [5-6] for two examples. However, the original fragmented design approach suffers from two major deficiencies. First, the placement of pixels on a generalized, rectilinear grid leads to the problem of diagonal touching. That is, pixels that touch diagonally lead to poor measurement/model agreement. Other research groups are also grappling with this diagonal touching issue [7]. Second, the convergence in the GA stage of the design process is poor for high pixel count apertures (>>100). This paper will present solutions to both of these shortcomings. First, alternate approaches to the discretization of the aperture area that inherently avoid diagonal touching will be presented. Second, an improvement to the usual GA mutation step that improves convergence for large pixel count fragmented aperture designs will be presented. Over the last few years, the authors have been involved with developing the use of the focused beam measurement system to measure antenna properties such as gain and pattern [8]. A series of improved, fragmented aperture antenna designs will be measured with the Compass Tech Focused Beam System and compared with the design predictions to validate the designs. References: [1] J. G. Maloney, M. P. Kesler, P. H. Harms, T. L. Fountain and G. S. Smith, “The fragmented aperture antenna: FDTD analysis and measurement”, Proc. ICAP/JINA Conf. Antennas and Propagation, 2000, pg. 93. [2] J. G. Maloney, M. P. Kesler, L. M. Lust, L. N. Pringle, T. L. Fountain, and P. H. Harms, “Switched Fragmented Aperture Antennas”, in Proc. 2000 IEEE Antennas and Propagations Symposium, Salt Lake City, 2000, pp. 310-313. [3] P. Friederich, L. Pringle, L. Fountain, P. Harms, D. Denison, E. Kuster, S. Blalock, G. Smith, J. Maloney and M. Kesler, “A new class of broadband planar apertures,” Proc. 2001 Antenna Applications Symp, Sep 19, 2001, pp. 561-587. [4] J. G. Maloney, M. P. Kesler, P. H. Harms and G. S. Smith, “Fragmented aperture antennas and broadband antenna ground planes,” U. S. Patent # 6323809, Nov 27, 2001. [5] N. Herscovici, J. Ginn, T. Donisi, B. Tomasic, “A fragmented aperture-coupled microstrip antenna,” Proc. 2008 Antennas and Propagation Symp, July 2008, pp. 1-4. [6] B. Thors, H. Steyskal, H. Holter, “Broad-band fragmented aperture phased array element design using genetic algorithms,” IEEE Trans. Antennas Propagation, Vol. 53.10, 2005, pp. 3280-3287. [7] A. Ellgardt, P. Persson, “Characteristics of a broad-band wide-scan fragmented aperture phased array antenna”, EuCAP 2006, Nov 2006, pp. 1-5. [8] J. Maloney, J. Fraley, M. Habib, J. Schultz, K. C. Maloney, “Focused Beam Measurement of Antenna Gain Patterns”, AMTA, 2012
ABSTRACT Spherical near-field error analysis is extremely useful in allowing engineers to attain high confidence in antenna measurement results. NSI has authored numerous papers on automated error analysis and spherical geometry choice related to near field measurement results. Prior work primarily relied on comparison of processed results from two different spherical geometries: Theta-Phi (0 =?= 180, -180 = f = 180) and Azimuth-Phi (-180 =?= 180, 0 = f = 180). Both datasets place the probe at appropriate points about the antenna to measure two different full spheres of data; however probe-to-antenna orientation differs in the two cases. In particular, geometry relative to chamber walls is different and can be used to provide insight into scattering and its reduction. When a single measurement is made which allows both axes to rotate by 360 degrees both spheres are acquired in the same measurement (redundant). They can then be extracted separately in post-processing. In actual fact, once a redundant measurement is made, there are not just two different full spheres that can be extracted, but a continuum of different (though overlapping) spherical datasets that can be derived from the single measurement. For example, if the spherical sample density in Phi is 5 degrees, one can select 72 different full sphere datasets by shifting the start of the dataset in increments of 5 degrees and extracting the corresponding single-sphere subset. These spherical subsets can then be processed and compared to help evaluate system errors by observing the variation in gain, sidelobe, cross pol, etc. with the different subset selections. This paper will show the usefulness of this technique along with a number of real world examples in spherical near field chambers. Inspection of the results can be instructive in some cases to allow selection of the appropriate spherical subset that gives the best antenna pattern accuracy while avoiding the corrupting influence of certain chamber artifacts like lights, doors, positioner supports, etc. Keywords: Spherical Near-Field, Reflection Suppression, Scattering, MARS. REFERENCES Newell, A.C., "The effect of measurement geometry on alignment errors in spherical near-field measurements", AMTA 21st Annual Meeting & Symposium, Monterey, California, Oct. 1999. G. Hindman, A. Newell, “Spherical Near-Field Self-Comparison Measurements”, Proc. Antenna Measurement Techniques Association (AMTA) Annual Symp., 2004. G. Hindman, A. Newell, “Simplified Spherical Near-Field Accuracy Assessment”, Proc. Antenna Measurement Techniques Association (AMTA) Annual Symp., 2006. G. Hindman & A. Newell, “Mathematical Absorber Reflection Suppression (MARS) for Anechoic Chamber Evaluation and Improvement”, Proc. Antenna Measurement Techniques Association (AMTA) Annual Symp., 2008. Pelland, Ethier, Janse van Rensburg, McNamara, Shafai, Mishra, “Towards Routine Automated Error Assessment in Antenna Spherical Near-Field Measurements”, The Fourth European Conference on Antennas and Propagation (EuCAP 2010) Pelland, Hindman, “Advances in Automated Error Assessment of Spherical Near-Field Antenna Measurements”, The 7th European Conference on Antennas and Propagation (EuCAP 2013)
This paper explores the accuracy capabilities of a two element phase interferometer measurement in a planar near-field scanner. Traditional phase interferometer applications utilize wide field of view antennas such as spirals making the utilization of planar near-field measurements less than ideal. In this application, high directivity antennas were utilized which allowed us to consider a planar near-field measurement solution. Leaving the AUT stationary and the stability of the planar near-field coordinate system were primary considerations in deciding to utilize a planar near-field measurement system. Typical interferometer performance metrics include comparing measured phase differences to ideal element phase differences at the same locations. Often the nominal drawing locations are used to generate the ideal element phase difference curves. The sensitivity of actual element vector displacement values versus ideal displacements can be reduced by deriving the best-fit displacement vector from the measured data and is utilized in the processing and reporting of results. This paper reviews the measurements, analysis techniques and results from this investigation and illustrates the capabilities of a planar near-field scanner to perform these types of measurements with a high degree of measurement fidelity.
This paper discusses the application of modern NF measurements and statistical analysis techniques to efficiently characterize the FF radiation pattern statistics of antennas and other EM emitters whose radiated EM fields vary erratically in a seemingly random manner. Such randomly-varying radiation has been encountered, for example, in measurements involving array antenna elements and reflector feed horn(s) containing active or passive devices that affect the relative phases and/or amplitudes of the pertinent RF signals in a non-deterministic manner [1-2]. In-Band (IB) as well as Out-Of-Band (OB) signals may be involved in some cases. Other possible randomly varying EM radiations include leakage from imperfectly-shielded equipment, connectors, cables, and waveguide runs [2- 4] Previous work at GTRI [5-7] has shown that computations of key FF radiation pattern statistics can be made based on NFFF transformations involving a) the sample average value of the complex electric field at each NF measurement point, b) the sample average value (a real number) of the standard deviation of the complex electric field at each NF measurement point, and c) the measured complex cross-covariance functions at all different NF measurement points. The key FF radiation pattern statistics of most interest are typically a) the statistical average FF radiation pattern, b) the standard deviation, c) the probability density function (p.d.f.), and d) the cumulative probability distribution (C.P.D.). Simulated data measurement protocols and the requisite statistical processing of the NF measured data will be presented and discussed in detail at the symposium. The NF cross-covariance functions introduce a new level of complexity in NF measurements and analysis that is absent for “deterministic” EM field measurements because the cross covariance functions must be measured and processed for all different NF measurement points on the NF surface to compute valid Pattern FF statistics. However, pairs of linear or circular probe arrays can be used to great advantage to achieve tolerable NF measurement times for the cross covariance functions and the aforementioned NF statistical quantities, thereby enabling valid computations of the FF pattern statistics. The use of dual probe arrays will be presented and discussed in detail and compared with mechanical scanning of two “single” probes over two NF measurement surfaces. A technique for estimating the cross-covariance functions will be presented and compared with exact values.
Methods for determining the uncertainty in antenna measurements have been previously developed and presented. The IEEE recently published a document [1] that formalizes a methodology for uncertainty analysis of near-field antenna measurements. In contrast, approaches to uncertainty analysis for antenna measurements on a compact range are not covered as well in the literature. Unique features of the compact range measurement technique require a comprehensive approach for uncertainty estimation for the compact range environment. The primary difference between the uncertainty analyses developed for near-field antenna measurements and an uncertainty analysis for a compact range antenna measurement lies in the quality of the incident plane wave illuminating the antenna under test from the compact range reflector. The incident plane wave is non-ideal in amplitude, phase and polarization. The impact of compact range error sources on measurement accuracy has been studied [2,3] and error models have been developed [4,5] to investigate the correlation between incident plane wave quality and the resulting measurement uncertainty. We review and discuss the terms that affect gain and sidelobe uncertainty and present a framework for assessing the uncertainty in compact range antenna measurements including effects of the non-ideal properties of the incident plane wave. An example uncertainty analysis is presented. Keywords: Compact Range, Antenna Measurement Uncertainty, Error Analysis References: 1. IEEE Standard 1720-2012 Recommended Practices for Near-Field Antenna Measurements. 2. Bingh,S.B., et al, “Error Sources in Compact Test Range”, Proceedings of the International Conference on Antenna Technologies ICAT 2005. 3. Bennett, J.C., Farhat, K.S., “Wavefront Quality in Antenna Pattern Measurement: the use of residuals.”, IEEE Proceedings Vol. 134, Pt. H, No. 1, February 1987. 4. Boumans, M., “Compact Range Antenna Measurement Error Model”, Antenna Measurement Techniques Association 1996 5. Wayne, D., Fordham, J.A, Mckenna, J., “Effects of a Non-Ideal Plane Wave on Compact Range Measurements”, Antenna Measurement Techniques Association 2014
Achieving a very large quiet zone across a wide frequency band, in a compact range system, requires a physically large reflector with a suitable surface accuracy. The size of the required reflector dictates attention to several important processes, such as how to manufacture the desired surface across a large area and the practicality of transportation and installation. This inevitably leads to the segmentation of the reflector into multiple panels; which must be fabricated, installed, and aligned to each other to conform to the required geometry. Performance predictions must take into account not only the surface accuracy of the individual panels but also their alignment errors. This paper presents the design approach taken on a recent project for a compact range system utilizing a blended rolled-edge reflector that produces a 5 meter quiet zone across a frequency range of 350 MHz to 40 GHz. It discusses the physical segmentation strategy, the fabrication methodology, the intermediate qualification of panels, the panel alignment technique, and the laser-based metrology methodology employed. Performance analysis approach and results will be presented for the geometry as conceived and then for the realized panelized reflector as machined and aligned.
Rapid advances in material fabrication capability, such as 3D printing, have made the realization of engineered complex media (i.e., anisotropic and bianisotropic materials) possible. One of the primary aspects prompting the interest in complex media is the added control over scattered electromagnetic fields due to the increase in the number of constitutive parameters. Isotropic media are characterized by the 2 well-known scalar parameters of permittivity and permeability. However, in general, it requires 18 and 36 parameters to describe anisotropic and bianisotropic media, respectively. Although the increase in parameter space provides more control over electromagnetic response, the penalty to pay is the added complexity in theoretical analysis when compared to isotropic media. One method that has been developed for the analysis of complex media is the six-vector field formalism which casts Maxwell’s equations into matrix form for ease of manipulation. Although this formalism handles fully populated permittivity and permeability tensors, inversion of a block 3x3 (i.e., 6x6) matrix is required which is mathematically intensive and physical insight can be obscured since a cofactor-based inversion is often employed in the solution process. The goal of this work is to develop a scalar potential formulation capable of handling gyrotropic media. Advantages and limitations of the formulation will be discussed and relevant examples will be provided to demonstrate the simplicity and physically-intuitive nature of the technique. Future work involving the use of the scalar potential formulation in the analysis of antenna, guided wave structures and material characterization of complex media will also be discussed to demonstrate the promising aspects of the technique.
In this paper an advanced analysis regarding the interaction between antennas installed on a spacecraft is presented. In particular, data coming from a GNSS satellite near field measurement campaign have been considered and the MV-INSIGHT software has been used to perform the analysis. Such a software, starting from the measured field of a DUT, computes equivalent currents on a surface conformal to the test object. The availability of the equivalent currents is a key point for an in depth analysis of DUT such as a spacecrafts since it allows to obtain exclusive diagnostic information like coupling between antennas and satellite structure. The near-field data have been collected in the Hybrid ESA RF and antenna Test Zone (HERTZ) at ESTEC. Such a hybrid NF/FF system has recently been installed in the existing dual reflector CPTR. The installed system has been designed to perform spherical, cylindrical and planar NF measurements in the broad frequencies range 0.4-50 GHz.
Crystallographic sample design of complex media influences material tensor properties. These properties offer amplitude, phase and polarization control of the electromagnetic (EM) fields. Previous works have evaluated crystallographic sample designs for isotropic, uniaxial and biaxial anisotropic media, each respective design offering more ways to control the fields. The tensor elements for these designs are all aligned along the main diagonal of the permittivity and/or permeability tensors. Additional field control can be obtained by producing materials that have off-diagonal tensor elements in addition to the aforementioned main diagonal elements. A monoclinic crystal sample design supports the existence of two off-diagonal elements and offers more field control than biaxial anisotropic media. In this work, field analysis is performed on media that possesses a monoclinic tensor element arrangement, demonstrating the additional control over EM fields as compared to biaxial anisotropic media. A monoclinic sample is then constituted using crystallographic symmetry. Future work will yield the development and analysis of a monoclinic sample material measurement capability.
Antenna measurement accuracies or error budgets are related to the signal-to-noise ratio of the measurement receiver. Signal-to-noise can be modelled taking two vectors, the intended signal and an interfering signal (i.e. from unwanted multipath propagation or simple noise), which superpose to the actual measured quantity. Although this approach is widely used, it is rarely discussed to its full extent. Instead, the error of the measured quantity is often estimated for high signal-to-noise ratios by applying worst case assumptions to the unwanted part. This excludes not only any statistical nature of the interfering signal but also the probability of the error appearance represented by its standard deviation. Especially when considering several error contributions in a total budget the adequate combination of different error probabilities yields a much more realistic result than adding single worst cases. Within this paper probability functions are analytically derived for measurement errors depending on the signal-to-noise ratio according to the aforementioned model. This yields a more sophisticated analysis of amplitude and phase errors having standard deviations for measured quantities. The confidence intervals of measurement errors are given with respect to varying signal-to-noise ratios. Limitations of the white noise synthesis with uniform phase and amplitude distributions are explained. Further, the applicability of worst case assumptions to the analytical solutions is discussed in the presence of high and low dynamic ranges. The derived expressions are statistically tested using Matlab calculations and compared to measurements with a vector network analyzer. The results are interpreted with respect to practical applications.
We have performed spherical and extrapolation scans of two antennas at 118 GHz using a commercial 6-axis robot. Unlike spherical scanning, linear extrapolations do not precisely conform to the natural circular movement about individual robot axes. To characterize the quality of the data, we performed dynamic position and orientation characterization of the robotic systems. A laser tracker is used to measure the probe antenna movement relative to the antenna under test, this information is used to continually update the position and posture of the probe during scanning. We correlated the laser tracker data with the mmWave insertion phase to validate dynamic measurement position results at speeds up to 11 mm/s. We previously demonstrated spherical measurements with this system. The extrapolation measurements presented here require more stringent accuracies for pointing that general pattern analysis
The source reconstruction or equivalents source method provides an accurate near-field representation of any radiating device in terms of equivalent electric and magnetic currents. The equivalent currents can be determined from measured near or far field data through a post-processing step involving the solution of an integral equation. The currents constitutes an accurate 3D electromagnetic model, maintaining near and far field properties of the measured device. A newly created link, enable the export of the model to a number of commercial computational electromagnetic (CEM) solvers in the form of a near-field Huygens box. Of special interest to the EMC community, equivalent current representation of measured devices are directly applicable in diagnostics/hot-spot finding and in the determination of radiated emission at any distance. The Huygens box, derived from measurements, is applicable in the simulation of emission in different scenarios when the device is in vicinity of different objects such as shielding, cables etc. This papers shows examples of diagnostics and emission analysis of a representative printed circuit board (PCB) based on commercially available near field measurement systems, post-processing and CEM tools.
Within the standard scheme for probe-corrected spherical data-processing, it has been found that for an efficient computational implementation it is necessary to restrict the characteristics of the probe pattern such that it contains only azimuthal modes for which µ = ±1 [1, 2, 3]. This first-order pattern restriction does not however extend to placing a limit on the polar index mode content and therefore leaves the directivity of the probe unconstrained. Clearly, when using this widely utilized approach, errors will be present within the calculated probe-corrected test antenna spherical mode coefficients for cases where the probe is considered to have purely modes for which µ = ±1 and where the probe actually exhibits higher order mode structure. A number of analysis [4, 5, 6, 7, 8] and simulations [9, 10, 11, 12] can be found documented within the open literature that estimate the effect of using a probe with higher order modes. The following study is a further attempt to develop guidelines for the azimuthal and polar properties of the probe pattern and the measurement configuration that can be utilized to reduce the effect of higher order spherical modes to acceptable levels. ? [1] P.F. Wacker, ”Near-field antenna measurements using a spherical scan: Efficient data reduction with probe correction”, Conf. on Precision Electromagnetic Measurements, IEE Conf. Publ. No. 113, pp. 286-288, London, UK, 1974. [2] F. Jensen, ”On the probe compensation for near-field measurements on a sphere”, Archiv für Elektronik und Übertragung-stechnik, Vol. 29, No. 7/8, pp. 305-308, 1975. [3] J.E. Hansen, (Ed.) “Spherical near-field antenna measurements”, Peter Peregrinus, Ltd., on behalf of IEE, London, 1988. [4] T.A. Laitinen, S. Pivnenko, O. Breinbjerg, “Odd-order probe correction technique for spherical near-field antenna measurements,” Radio Sci., vol. 40, no. 5, 2005. [5] T.A. Laitinen, O. Breinbjerg, “A first/third-order probe correction technique for spherical near-field antenna measurements using three probe orientations,” IEEE Trans. Antennas Propag., vol. 56, pp. 1259–1268, May 2008. [6] T.A. Laitinen, J. M. Nielsen, S. Pivnenko, O. Breinbjerg, “On the application range of general high-order probe correction technique in spherical near-field antenna measurements,” presented at the 2nd Eur. Conf. on Antennas and Propagation (EuCAP’07), Edinburgh, U.K. Nov. 2007. [7] T.A. Laitinen, S. Pivnenko, O. Breinbjerg, “Theory and practice of the FFT/matrix inversion technique for probe-corrected spherical near-field antenna measurements with high-order probes”, IEEE Trans. Antennas Propag., vol. 58,, No. 8, pp. 2623–2631, August 2010. [8] T.A. Laitinen, S. Pivnenko, “On the truncation of the azimuthal mode spectrum of high-order probes in probe-corrected spherical near-field antenna measurements” AMTA, Denver, November 2012. [9] A.C. Newell, S.F. Gregson, “Estimating the effect of higher order modes in spherical near-field probe correction”, AMTA 34th Annual Meeting & Symposium, Seattle, WA, October. 2012. [10] A.C. Newell, S.F. Gregson, “Higher Order Mode probes in Spherical Near-Field Measurements”, EuCAP, Gothenburg, April, 2013. [11] A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction”, AMTA 35th Annual Meeting & Symposium, Seattle, WA, October. 2013. [12] A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Azimuthal Modes in Spherical Near-Field Probe Correction”, EuCAP, The Hague, April, 2014.
Active S-parameters represent reflection coefficients of elements in an active phased array antenna under various element excitations. Active S-parameters can be calculated for any array excitation if the S-parameter matrix is fully characterized. In practice, the entries of this matrix can usually be gathered through measurements with a 2-port vector network analyzer (VNA). However, depending on the number of elements in the phased array, the number of measurements can be extremely large in order to obtain a full S-matrix. For a phased array consisting of N elements, N(N-1)/2 measurements with a 2-port VNA are required to obtain N-by-N S-matrix, assuming the antenna elements are reciprocal. In order to avoid large number of measurements, a scenario consisting of S-parameter measurements for the center element and also some elements located at the edges and corners of the array is proposed under a flexible predefined error criterion. Then, measured S-parameters are used to obtain N-by-N S-matrix via exploitation of the array symmetry and periodicity which is required to calculate the active S-parameters of the whole array. A fabricated uniform planar Vivaldi array with 112 elements is measured with the proposed scenario and calculated active S-parameters are compared with those obtained from full-wave analysis.
Constitutive parameter characterization of a biaxial anisotropic material using a rectangular waveguide requires three separate samples; each one a different orientation of the parent biaxial anisotropic sample. The Waveguide Rectangular to Waveguide Square (WRWS) characterization method is an alternative, more efficient method, to the rectangular waveguide method because the WRWS method requires only one cube sample of biaxial anisotropic material to perform complete parameter extraction. This cube sample fits uniformly without gaps in the waveguide sample holder and can be indexed to accommodate all orientations required for characterization. The WRWS waveguide transitions insure that only single (TE10) modes are present and thus leads to closed form solutions for the material properties - an advantage over other existing techniques requiring higher-order modal analysis and subsequent numerical root search for extraction. Each WRWS transition mounts to the sample holder and the waveguide test ports of a Vector Network Analyzer and is calibrated using a TRL technique. A biaxial anisotropic test sample was designed based upon crystallographic symmetry, mixing theory and verified in rectangular waveguide measurements. WRWS test data is collected and constitutive parameters are extracted from each orientation of the biaxial anisotropic cube. This method of extracting biaxial anisotropic constitutive parameters using the WRWS system is evaluated in both experiment, simulation and validates the WRWS method. Theory, experimental and simulated results are presented to show that a cubic sample and WRWS measurement system can be efficiently and effectively used to measure biaxial anisotropic materials.
In recent years a number of analyses and simulations have been published that estimate the effect of using a probe with higher order azimuthal modes with standard probe corrected spherical transformation software. In the event the probe has higher order modes, errors will be present within the calculated antenna under test (AUT) spherical mode coefficients and the resulting asymptotic far-field parameters [1, 2, 3, 4] where the simulations were harnessed to examine these errors in detail. Within those studies, a computational electromagnetic simulation (CEM) was developed to calculate the output response for an arbitrary AUT/probe combination where the probe is placed at arbitrary locations on the measurement sphere ultimately allowing complete near-field acquisitions to be simulated. The planar transmission equation was used to calculate the probe response using the plane wave spectra for actual AUTs and probes derived from either planar or spherical measurements. The planar transmission formula was utilized as, unlike the spherical analogue, there is no limitation on the characteristics of the AUT or probe thereby enabling a powerful, entirely general, model to be constructed. This paper further extends this model to enable other measurement configurations and errors to be considered including probe positioning errors which can result in ideal first order probes exhibiting higher order azimuthal mode structures. The model will also be used to determine the accuracy of the Chu and Semplak near-zone gain correction [5] that is used in the calibration of pyramidal horns. The results of these additional simulations are presented and discussed. Keywords: near-field, antenna measurements, near-field probe, spherical alignment, spherical mode analysis. REFERENCES A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction”, Antenna Measurement Techniques Association (AMTA) 34th Annual Meeting & Symposium, Bellevue, Washington October 21-26, 2012. A.C. Newell, S.F. Gregson, “Higher Order Mode Probes in Spherical Near-Field Measurements”, 7th European Conference on Antennas and Propagation (EuCAP 2013) 8-12 April 2013. A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction”, Antenna Measurement Techniques Association (AMTA) 35th Annual Meeting & Symposium, Columbus, Ohio, October 6-11, 2013. A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Azimuthal Modes in Spherical Near-Field Probe Correction”, The 8th European Conference on Antennas and Propagation (EuCAP 2014) 6-11 April 2014. T.S. Chu, R.A. Semplak, “Gain of Electromagnetic Horns,’’ Bell Syst. Tech. Journal, pp. 527-537, March 1965