Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
The 3D reconstruction algorithm of DIATOOL, with its higher-order Method of Moments-based implementation, reconstructs extreme near fields and surface currents on arbitrary 3D surfaces enclosing the antenna under test (AUT) from its measured radiated field. This is a valuable analysis and diagnostics tool for the antenna engineer to speed up the antenna prototyping cycle and identify errors in the manufactured AUTs, since the 3D reconstruction can solve a number of problems which traditional microwave holography cannot handle, namely: Accurate and detailed identification of array malfunctioning due to the enhanced spatial resolution of the reconstructed fields and currents Filtering of the scattering from support structures and feed network leakage A number of papers published over the past four years have shown these features in detail. At the same time it was observed that the spherical wave expansion (SWE) of the field radiated by the currents reconstructed by DIATOOL always provides a SWE power spectrum that looks noise-free. This phenomenon was observed for all the antennas on which the 3D reconstruction was applied, and it was explained as being an effect of the 3D reconstruction algorithm, which uses the a-priori information that all sources are contained inside the reconstruction surface. However, since real measured data were always used as input, it was not possible to prove that the SWE power spectrum of the reconstructed currents coincided with the one that would be obtained from noise-free measurements. The purpose of the present paper is thus to investigate in detail the noise filtering capabilities of the 3D reconstruction algorithm of DIATOOL. Models of several antennas, differing in size and type, were set up in GRASP with noise at different levels added to the radiated field. The noisy field was then given as input to DIATOOL and the SWE coefficients and the power spectra of the reconstructed currents were compared with the noise-free results coming from GRASP. Moreover, the effect of the varying noise level on the obtainable resolution was investigated.
Typical RF cables found in most labs have an expanded PTFE dielectric material, commonly known as Teflon. This material works well for most RF applications, however as engineers we know there’s always a “gotcha.” The Teflon Knee is a very old problem that is manifested as a phase variation in a very small temperature range. Unfortunately this occurs close to room temperature, 19 to 23 degrees Celsius in particular. This makes accurate and repeatable phase measurements a daunting task near those temperatures.???? The phenomena is caused at the molecular level where the material goes through a phase state change (long molecule chains change their twisting slightly). A recently developed network analyzer accessory, Agilent CalPods, makes accurate observations of the effects of Teflon Knee possible. The author was the first to use a CalPods system in Raytheon and experiment with various RF cables in an environmental chamber. Teflon is a registered trademark of DuPont Co. 5/12/2014 Copyright © 2014 Raytheon Company. All rights reserved. Customer Success Is Our Mission is a registered trademark of Raytheon Company.???????????
In late 2013, the Federal Aviation Administration (FAA) announced that airline passengers would be allowed to use personal electronic devices (PEDs) during all phases of commercial flights. However, to gain FAA approval for PED usage, airlines were required to demonstrate that their aircraft were sufficiently immune to potential interference from PEDs. As a result of the FAA requirement, Delta Air Lines (DAL) and the Georgia Tech Research Institute (GTRI) collaborated to develop and implement a certification testing program based on the industry accepted standard for PED testing, RTCA/DO-307 “Aircraft Design and Certification for Portable Electronic Device (PED) Tolerance”. Delta and GTRI accomplished certification of the Delta fleet by tailoring DO-307 to meet Delta’s needs of testing eleven flight active aircraft within a short timeframe. GTRI was able to identify ways to improve test efficiency and implement changes to the test program in response to different aircraft configurations and active flight schedules. This paper will discuss the program requirements, test system architecture, component selection, test methodology and test results for two critical components of aircraft Instrument Landing System (ILS); the Localizer and Glide Slope systems.
Near field Radar Cross Section (RCS) measurements and Inverse Synthetic Aperture Radar (ISAR) are used in this study to obtain geometrically correct images and far field RCS. The methods and the developed algorithms required for the imaging and the RCS extraction are described and evaluated in terms of performance in this paper. Most of the RCS measurements on full scale objects that are performed at our measurement ranges are set up at distances shorter than those given by the far field criterion. The reasons for this are e.g., constraints in terms of budget, available equipment and ranges but also technical considerations such as maximizing the signal to noise in the measurements. The calibrated near-field data can often be used as recorded for diagnostic measurements. However, in many cases the far field RCS is also required. Data processing is then needed to transform the near field data to far field RCS in those cases. A straightforward way to image the RCS data recorded in the near field is to use the backprojection algorithm. The amplitudes and locations for the scatterers are then determined in a pixel by pixel imaging process. The most complicated part of the processing is due to the near field geometry of the measurement. This is the correction that is required to give the correct incidence angles in all parts of the imaged area. This correction has to be applied on a pixel by pixel basis taking care to weigh the samples correctly. The images obtained show the geometrically correct locations of the target scatterers with exceptions for some target features e.g., when there is multiple or resonance scattering. Separate features in the images can be gated and an inverse processing step can be performed to obtain the far field RCS of the full target or selected parts of the target, as a function of angle and frequency. Examples of images and far field RCS extracted from measurements on full scale targets using the ISAR processing techniques described in this paper will be given.
Equivalent isotropically radiated power (EIRP) and Saturating flux density (SFD) are two system level parameters often sought during characterizing of spacecraft systems. The EIRP quantity is the power that an isotropic radiator will have to transmit to lead to the same power density that the AUT will effect at a specific angle of interest. A convenient measurement technique is to set up a standard gain antenna as receiver in the far-field of an AUT and to then determine EIRP by measuring the power at the port of the standard gain receiving antenna. Since the distance is known the EIRP can be calculated. SFD is the flux required to saturate the receiver of the antenna under test and is also usually determined on a far-field range. The philosophy of this measurement is to determine the saturation level of the receiver and this is typically achieved by gradually increasing the input power level of the transmitter. This process continues as long as the receiver response linearly tracks the increase in power of the transmitter and is terminated once the receiver is saturated. Thus, SFD can be interpreted as being the receive system parameter analogy of the transmit system parameter EIRP. There is a common misconception that these parameters cannot be measured on a near-field range and that they require far-field (or far-field equivalent, i.e. compact range) conditions for a valid measurement to be made. However, the principles for measuring both of these parameters in a planar near-field range (PNF) were presented in [1]: An EIRP technique is presented in [1] equation 32 and this approach relies on a complex integration of the measured near-field power, the near-field probe gain and a single power measurement at a reference location. A SFD technique is presented in [1] equation 39. This technique also relies on a complex integration of the measured near-field power, the near-field probe gain and a single transmitting probe power measurement at a reference location. Although these descriptions are theoretically concise their execution is not obvious [2] and as a result, there still seems to be hesitation in making (and trusting) these measurements in industry. This paper intends to provide further insight into measuring these two parameters in a PNF range and offers test procedures outlining the steps involved in doing so. The principle goal is to offer further explanation to illuminate the underlying principles. The work presented here is not new, but is presented as a tutorial on this illusive subject. [1] Newell, Ward and McFarlane, “Gain and Power Parameter Measurements Using Planar Near-Field Techniques”, IEE APS Transactions, Vol 36, No. 6, June 1988. [2] Masters & Young, “Automated EIRP measurements on a near-field range”, Antenna Measurement Techniques Association Conference, September 30 - October 3, 1996.
Antenna alignment for near-field scanning was typically done at NIST with multiple instruments (theodolites, electronic levels, motor encoders) to align multiple stacked motion stages (linear, rotation). Many labs and systems are now using laser trackers to measure ranges and perform periodic compensation across the scan geometry. We are now seeing the use of laser trackers with 3D coordinate metrology to align ranges and take positional data. We present the alignment techniques and positional accuracy and uncertainty results of a mmWave antenna scanning system at 183 GHz. We are using six degree-of-freedom (6DOF) AUT and Probe measurements (x, y, z, yaw, pitch, roll) to align the AUT and then to align the scan geometry to the AUT. We are using a combination of 3DOF laser tracker measurements with a combined 6DOF laser tracker/photogrammetry sensor. We combine these measurements using coordinated spatial metrology to assess the quality of each motion stage in the system, tie the measurements of each individual alignment together, and to assess scan geometry errors for position and pointing. Finally we take in-situ 6DOF position measurements to assess the positional accuracy to allow for positional error correction in the final pattern analysis. The knowledge of the position and errors allow for the correction of position and alignment of the probe at every point in the scan geometry to within the repeatability of the motion components (~30 µm). The in-situ position knowledge will eventually allow us to correct to the uncertainty of the measurement (~15 µm). Our final results show positioning errors on the spherical scan surface have an average error of ~30 µm with peak excursions of ~100 µm. This robust positioning allows for accurate analysis of the RF system stability. Our results show that at 183 GHz, our RF repeatability with movement over 180° orientation change with a 600 mm offset to be less than ±0.05 dB and ±5°.
Performance requirements for compact ranges are typically specified as metrics describing the quiet zone's electromagnetic-field quality. The typical metrics are amplitude taper and ripple, phase variation, and cross polarization. Acceptance testing of compact ranges involves phase probing of the quiet zone to confirm that these metrics are within their specified limits. It is expected that if the metrics are met, then measurements of an antenna placed within that quiet zone will have acceptably low uncertainty. However, a literature search on the relationship of these parameters to resultant errors in antenna measurement yields limited published documentation on the subject. Various methods for determining the uncertainty in antenna measurements have been previously developed and presented for far-field and near-field antenna measurements. An uncertainty analysis for a compact range would include, as one of its terms, the quality of the field illuminating on the antenna of interest. In a compact range, the illumination is non-ideal in amplitude, phase and polarization. Error sources such as reflector surface inaccuracies, chamber-induced stray signals, reflector and edge treatment geometry, and instrumentation RF leakage, perturb the illumination from ideal.
The measurement community can use advanced simulation techniques to minimize both the time and financial investment necessary to design a custom compact antenna test range (CATR), while simultaneously optimizing performance. Traditionally, engineers have analyzed parabolic reflectors, a collimating device installed in CATRs, with approximate methods similar to ray-tracing, physical optics and physical theory of diffraction due to the practical limitations of the available resources. However, recent technological advances facilitate the rigorous analysis of electrically large parabolic reflectors. Computational resources (i.e. processors and memory) continue to offer improved performance at reduced cost. In addition, rigorous numerical solvers (i.e. the Multilevel Fast Multipole Method (MLFMM)), have become available in commercial software such as FEKO. Simulations employing these numerical solvers extend previous research by characterizing the quiet zone when operating offset-fed parabolic reflectors. The gain-transfer method is then emulated with an antenna under test (AUT). Several reflector edge treatments (e.g. serrated, blended-rolled) are considered to better understand performance trade-offs. Simulating an antenna measurement technique provides the insight necessary to identify and quantify potential error sources. The convergence between measured and simulated antenna performance characteristics can therefore be expedited with improved reliability.
Antenna and Radar Cross Section (RCS) measurements are often required for orientation sets (cuts) that are difficult or impossible to produce with the positioning instrumentation available in a given lab. This paper describes a general coordinate transform, combined with a general polarization rotation to correct for these orientation differences. The technique is general, and three specific examples from actual test programs are provided. The first is for an RCS measurement of a component mounted in a flat-top test fixture. The component is designed to be mounted in a platform at an orientation not feasible for the flat-top fixture, and the test matrix calls for conic angle cuts of the platform. The transforms result in a coordinated, simultaneous two-axis motion profile and corresponding polarization rotations yielding the same information as if the component had been mounted in the actual platform. The second example is for a pattern measurement of an antenna suite mounted on a cylindrical platform (such as a projectile). In this case, the test matrix calls for a roll-cut, but the range positioning system does not include a roll positioner. The transforms again result in a coordinated, simultaneous two-axis motion profile and corresponding polarization rotations to provide the same information as the required roll-cut but without the use of a roll positioner. Finally, the third example is for an antenna pattern measurement consisting of an extremely large number of cuts consisting of conic yaw cuts, roll cuts and pitch cuts. The chosen method involves the use of the Boeing string suspension system to produce great-circle cuts at various pitch angles combined with the use of the coordinate and polarization transforms to emulate, off-line, any arbitrary cut over any axis or even multiple axes. Keywords: Algorithm, Positioning, Polarization, Coordinates, RCS
Driven by the mobile data communications needs of market broadband antennas at the upper frequency bands are already state-of-the-art, e.g. at the Ka-Band. For the characterization of an antenna the antenna gain is one of the major test parameters. This measurement task is already challenging for standard applications at the Ka-Band. However, for the calibration of remote station antennas utilized in high precision test facilities, e.g. the compact range, even higher measurement accuracies are typically required in order to fulfil the overall system performance within the later test facility. Therefore the requirement for this investigation is to improve the measurement set-up and also the steps to get a failure budget which is better than ± 0.15 dB. Every antenna gain measurement technique is affected by required changes in the measurement setup, e.g. the Device under Test (DUT) or the remote station, respectively. This results for example in a variation of mismatch with resulting measurement errors. To determine and compensate the occurred mismatches, the scattering parameters of the involved components have to be measured and be evaluated with a corresponding correction formula. To quantify the effect for the gain measurement accuracy the remaining uncertainty of the mismatch correction values is examined. Another distortion is caused by multiple reflections between the antenna apertures. To reduce this error source, four additional measurements each with a decreased free space distance should be performed. In addition to the common methods, this paper explains in detail an advanced error correction method by using the singular value decomposition (SVD) and compares this to the standard mean value approach. Finally the restricted distance between both antennas within the applied anechoic far-field test chamber has to be analysed very critically and optionally corrected for the far-field gain at an infinite distance in case the measurement distance is fulfilling the minimum distance requirement, only. The paper will discuss all major error contributions addressed above, show correction approaches and verify these algorithms with exemplary gain measurements in comparison to the expected figures.
Compact Mini Vector Network Analyzer (VNA) frequency extension modules have been developed for all frequency bands from WR-15 though WR-5.1, with prototypes in development for higher bands. These modules are available in both Mini transmit-receive (Tx-Rx) for full two-port S-parameter measurements and smaller Micro receive-only (Rx) configurations. A common setup, for example, would be to combine a Mini Tx-Rx with a Micro Rx to provide S11 and S21 measurement capability. The modules are designed to be used up to 8m away from the VNA system with excellent amplitude and phase stability, making them well suited for antenna range applications. The WR-15/WR-12/WR-10 family of Mini and Micro extension modules each cover greater than the nominal waveguide band—46-79 GHz for WR-15, 55-95 GHz for WR-12, and 65-116 GHz for WR-10. The Mini Tx-Rx modules provide 120dB dynamic range, +/- 0.15 dB amplitude stability, +/- 2 degree phase stability, and +6dBm test port power. They measure 1.5” x 3.0” x 8.5” with 1.2kg mass and require only a single +9V supply. The Micro Rx module is a single 300g 2.5” x 1.0” x 0.7” block with two coaxial connections and a DC +5V pin while still providing the same dynamic range and stability as the Mini Tx-Rx modules. For antenna range applications or other high path loss environments, the attenuator can be removed from the Micro Rx input to give 150 dB effective dynamic range. A WR-8.0/WR-6.5/WR-5.1 (90-140 GHz / 110-170 GHz / 140-220 GHz) family of Mini Tx-Rx and Micro Rx extension modules has also been developed with the same form factor as the lower-frequency family—smaller Minis for these bands are currently being developed. The WR-8.0/6.5/5.1 extender family also provides 120 dB dynamic range and excellent stability. Standard-size Tx-Rx and Rx extension modules, still quite compact at 3” x 5” x 11”, are also available for all waveguide bands up through WR-1.0/WM-250 (750-1100 GHz). Mini and Micro extension modules for bands above WR-5.1 are currently in development, with some modules such as a WR-3.4 Micro Rx already available.
When performing far field or near field antenna measurements on large antennas, it is often necessary to have various types of mechanical positioning systems to achieve the required hemispheric scans. Measurement systems employing a single-arm gantry, a dual-arm gantry, a fixed arch moving probe, or a fixed arch multi-probe have been paired with either an azimuth positioner or a vehicle turntable to provide hemispheric scanning of the object being tested. This paper will highlight the key characteristics of various scanning methods making comparisons between the different techniques. Positioning and system accuracy, speed, stowing ability, calibration, frequency range, upgradability, relative cost and other key aspects of the various techniques will be discussed in detail to help the end user during the system design and selection process. In addition, the paper will highlight novel hemispheric and truncated spherical scanning approaches. In many applications, the success of the entire project often centers on the judicious selection of the positioning subsystem. This paper will provide guidance toward making the proper selection of the scanning concept as well as of the positioning system.
The Ohio State University ElectroScience Laboratory in partnership with Syntonics Corporation have developed a wide band reflectarray antenna system that uses true time delay elements. The reflectarray antenna is a thin space-fed flat panel with an array of antenna elements printed on it. Each antenna element has a microstrip transmission line attached to it that is terminated with an open circuit. Each length of transmission line forms a delay line, so that the signal re-radiated from each antenna element is controlled in time by the length of this line. The final result is a very thin (1 mm) and lightweight wide-band reflectarray antenna. We will show the design, the theoretical modeling of the individual reflecting elements and of the larger array, and finally, the experimental construction and gain measurements of the resulting test antenna. Issues such as main beam and sidelobe effects due to delay line length error statistics as well as power handling will be discussed.
The near-field – far-field (NF–FF) transformation with spherical scanning is particularly interesting, since it allows the reconstruction of the complete radiation pattern of the antenna under test (AUT) [1]. In this context, the application of the nonredundant sampling representations of the electromagnetic (EM) fields [2] has allowed the development of efficient spherical NF–FF transformations [3, 4], which usually require a number of NF data remarkably lower than the classical one [1]. In fact, the NF data needed by this last are accurately recovered by interpolating a minimum set of measurements via optimal sampling interpolation (OSI) expansions. A remarkable measurement time saving is so obtained. 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. As a consequence, 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 reconstruction in the case of cylindrical and spherical surfaces. The latter relies on the singular value decomposition method, does not exhibit the above limitation, but can be conveniently applied only if the uniform samples recovery can be reduced to the solution of two independent one-dimensional problems [6]. Both the approaches have been applied and numerically compared with reference to the positioning errors compensation in the spherical NF–FF transformation for long antennas [7] using a prolate ellipsoidal AUT modelling. The goal of this work is just to validate experimentally the application of these approaches to the NF–FF transformation with spherical scanning for elongated antennas [4], using a cylinder ended in two half-spheres for modelling them. The experimental tests have been performed in the Antenna Characterization Lab of the University of Salerno, provided with a roll over azimuth spherical NF facility supplied by MI Technologies, and have fully assessed the effectiveness of both the approaches. [1] J.E. Hansen, ed., Spherical Near-Field Antenna Measurements , IEE Electromagnetic Waves Series, London, UK, Peter Peregrinus, 1998. [2] 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, 1998. [3] O.M. Bucci, F. D’Agostino, C. Gennarelli, G. Riccio, C. Savarese, “Data reduction in the NF–FF transformation technique with spherical scanning,” Jour. Electr. Waves Appl ., vol. 15, pp. 755-775, June 2001. [4] F. D’Agostino, F. Ferrara, C. Gennarelli, R. Guerriero, M. Migliozzi, “Effective antenna modellings for NFFF transformations with spherical scanning using the minimum number of data,” Int. Jour. Antennas Prop ., vol. 2011, Article ID 936781, 11 pages, 2011 [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, G. Riccio, C. Savarese, “Far field reconstruction from nonuniform plane-polar data: a SVD based approach,” Electromagnetics, vol. 23, pp. 417-429, July 2003 [7] F. D’Agostino, F. Ferrara, C. Gennarelli, R. Guerriero, M. Migliozzi, “Two techniques for compensating the probe positioning errors in the spherical NF–FF transformation for elongated antennas,” The Open Electr. Electron. Eng. Jour. , vol. 5, pp. 29-36, 2011.
In the recent years, many efforts have been spent to reduce the time required for the near-field data acquisition, since such a time is nowadays very much greater than that required to perform the transformation. In this context, planar spiral scanning techniques exploiting continuous and synchronized movements of the positioning systems of the probe and antenna under test (AUT) have been proposed [1-4] to significantly reduce the measurement time. They are based on the nonredundant sampling representations of electromagnetic fields [5, 6] and use optimal sampling interpolation formulas to efficiently recover the data required by the classical plane-rectangular near-field – farfield (NF–FF) transformation [7] from those acquired along the spiral. In particular, the AUT has been modelled as enclosed in a sphere in [1, 2], whereas an oblate ellipsoid has been considered in [3, 4]. When dealing with a quasi-planar AUT, this last antenna modelling results to be more effective from the truncation error and data reduction viewpoints with respect to the spherical one. As a matter of fact, it is able to reduce the redundancy induced by the spherical modelling for such a kind of antennas and allows to consider measurement planes at distances less than one half of the antenna maximum size, thus lowering the error related to the truncation of the scanning surface. The goal of this work is to experimentally validate the NF–FF transformation with planar spiral scanning which makes use of the ellipsoidal AUT modelling [3]. The experimental tests will be performed in the Antenna Characterization Lab of the University of Salerno, equipped with a planepolar NF facility system, besides the cylindrical and spherical ones, and will fully assess the effectiveness of this technique, as well as, of that based on the spherical modelling, that can be obtained as particular case from the oblate one when the ellipsoid eccentricity goes to zero. [1] O.M. Bucci, F. D’Agostino, C. Gennarelli, G. Riccio, and C. Savarese, “Probe compensated far-field reconstruction by near-field planar spiral scanning,” IEE Proc. – Microw., Antennas and Propagat. , vol. 149, pp. 119–123, 2002. [2] F. D’Agostino, C. Gennarelli, G. Riccio, and C. Savarese, “Theoretical foundations of near-field–far-field transformations with spiral scannings,” Prog. in Electromagn. Res. , vol. 61, pp. 193-214, 2006 [3] F. D’Agostino, F. Ferrara, C. Gennarelli, R. Guerriero, and M. Migliozzi, “An effective NF-FF transformation technique with planar spiral scanning tailored for quasi-planar antennas,” IEEE Trans. Antennas Propagat ., vol. 56, pp. 2981-2987, 2008. [4] F. D’Agostino, F. Ferrara, C. Gennarelli, R. Guerriero, and M. Migliozzi, “The unified theory of near–field – far–field transformations with spiral scannings for nonspherical antennas,” Prog. in Electromagn. Res. B, vol. 14, pp. 449-477, 2009. [5] O.M. Bucci, C. Gennarelli, and 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, 1998. [6] O.M. Bucci and C. Gennarelli, “Application of nonredundant sampling representations of electromagnetic fields to NF-FF transformation techniques,” Int. Jour. of Antennas and Propagat. , vol. 2012, ID 319856, 14 pages. [7] D. T. Paris, W. M. Leach, Jr., and E. B. Joy, “Basic theory of probe-compensated near-field measurements,” IEEE Trans. Antennas Propagat., vol. AP-26, pp. 373-379, May 1978.
?A wide band open boundary quad-ridge horn is investigated to provide multi-octave bandwidth operation for a dual reflector compact range. A commercial off-the-shelf (COTS) multi-octave RF feed was selected and optimized to the existing sub-reflectors. The selection requirements of the COTS multi-octave RF Feed are first determined from a geometric optic (GO) analysis method. These results are used to provide an upper bound of the feed directivity affecting target quiet zone (QZ) performance. Physical Optic (PO) and Physical Theory of Diffraction (PTD) analysis that includes the reflectors serrations are then performed to derive the feed requirements to best meet the QZ specifications. This paper presents the use of COTS multi-band RF feed in a compact range that is properly optimized to the sub-reflectors providing frequency bandwidth to meet QZ performance specifications. Comparisons of these analysis to the QZ field probe measurements of the compact range QZ amplitude ripple phase and scan size comparisons are made to verify the compact range COTS RF feed selection. A multi-octave band RF feed in a compact range application enables highly accurate and efficient test measurement capability for characterization of active arrays over a wide bandwidth in real time.
A three-step equiangular (120º) phase shifting holography (EPSH) technique is proposed for THz antenna near-field/far-field prediction. The method is attractive from the viewpoint of receiver sensitivity, phase accuracy over the entire complex plane, simplified detector array architecture, as well as reducing planarity requirements of the near-field scanner. Numerical modeling is presented for the holographic receiver performance, using expected phase shift calibrations errors and phase shift noise. The receiver model incorporates responsivity and thermal noise specifications of a commercial Schottky diode detector. Additionally, simulated near-field patterns at 372GHz demonstrate the convenience of the method for accurate and high dynamic range THz near-field/far-field predictions, using a phase-shifter calibrated to ±0.1°.
We propose a technique which achieves highly accurate near-field data as well as far-field patterns despite the positioning inaccuracy of the scanner in the antenna near-field measurements. The method involves position sensing hardware in conjunction with data processing software. The underlying theory is provided by the Field Mapping Algorithm (FMA), which transforms exactly the measured field data on a conventional planar, spherical, or cylindrical surface, indeed on any enclosing surface, to any other surface of interest. In our modified near-field scanning system, a position recording laser device is attached to the probe. The positions of data grid points are thus found and recorded along with the raw RF data. The raw data acquired over an irregular, imperfect surface is subsequently converted exactly to a designated, regular surface of canonical type based on the FMA and its associated position information. Once the near-field data is determined at all required grid points, the far-field pattern per se is obtained via a conventional near-field-to-far-field transformation. Moreover, and perhaps just as importantly, the interplay between our FMA and the free-form position/RF recording methodology just described allows us to bypass entirely the arduous task of strict antenna alignment. The free-form position/RF data are simply propagated by the FMA software to some perfectly aligned reference surface ideally adapted as a springboard for any intended far-field buildup. Our proposed marriage of a standard scanning system and a position recorder, with otherwise imperfect RF/location data restored to ideal status under the guidance of the FMA, clearly offers the advantage of high precision at minimal equipment cost. It is, simply stated, a win-win budget/accuracy RF measurement solution. Two analytic examples and one measurement case are given for demonstration. The first example is a circular aperture within an infinite conducting plane, the second is a 10 lambda x 10 lambda dipole array antenna. The measurement case involves a waveguide slot array antenna. In all three cases, the near-field data were deliberately acquired over imperfectly located grid points. The FMA was then applied to obtain near-field data at the preferred, regularly arranged grid points from these position compromised values. Excellent grid-to-grid near-field comparison and calculated far-field results were obtained.
In recent times, planar near-field antenna measurements have largely been performed within fully absorber lined anechoic chambers. However this is a comparatively recent development as, due to the nature of the electromagnetic radiation when measuring medium to high gain antennas, one can often obtain excellent results when testing within only a partially absorber lined chamber [1], or in some cases even when using absorber placed principally behind the acquisition plane. As absorber can be bulky and costly, optimizing its usage often becomes a significant factor when planning a new facility. This situation becomes more pressing when the designated test environment is not exclusively devoted to antenna pattern testing with non-ideal absorber coverage being, in some cases, mandated, c.f. EMC testing. Planar test systems lend themselves to deployment within multipurpose installations as they are routinely constructed so as to be portable [2] thereby allowing partial or perhaps complete removal of the test system between measurement campaigns. This paper will present measured data taken using a number of different planar antenna test systems with and without anechoic chambers to summarize what is achievable and to provide design guidelines for testing within non-ideal anechoic environments. NSI’s Planar Mathematical Absorber Reflection Suppression (MARS) technique [3, 4] will be utilized to show additional improvements in performance that can be achieved through the use of modern sophisticated post processing. Keywords: Planar Near-Field, Reflection Suppression, Scattering, MARS. REFERENCES S.F. Gregson, A.C. Newell, G.E. Hindman, M.J. Carey, “Extension of The Mathematical Absorber Reflection Suppression Technique To The Planar Near-Field Geometry”, AMTA, Atlanta, October 2010. G.E. Hindman, “Applications of Portable Near-Field Antenna Measurement Systems”, AMTA, October, 1991. S.F. Gregson, A.C. Newell, G.E. Hindman, “Advances In Planar Mathematical Absorber Reflection Suppression”, AMTA, Denver, Colorado, October 2011. S.F. Gregson, A.C. Newell, G.E. Hindman, P. Pelland, “Range Multipath Reduction In Plane-Polar Near-Field Antenna Measurements”, AMTA, Seattle, October 2012.
The electromagnetic compatibility (EMC) problems are becoming more challenging and noticeable due to the increasing complexity of integrated circuits (IC). Currently, most electromagnetic interference (EMI) standards specify that the measurements must be performed in the far field which is time consuming and expensive for the use of semi-anechoic chambers or open area test site. While near-field measurement is usually fast and much more flexible, especially for the complex structures, the near-field results could be obtained more efficiently for built-in ICs. The transformation between near-field and far-field data is of great significance as long as the near-field data is measured. Many methods including near-field scanning method and Huygens’ equivalence method are used to complete the transformation from near-field data to far-field radiation. However, the near-field scanning method is inherent complex and requires strict mathematical derivation, which is difficult to handle for some practical cases. Huygens’ equivalence method is restricted by the location of observation point and the results are hardly obtained under scanning plane. In contrast, near-field to far-field transformation based on inverse method appears to be more desirable by reconstructing a dipole-moment model instead of an IC. The dipole-moment model can be used to predict the far-field data, but also can be incorporated into a numerical full-wave tool as an equivalent source for complex systems. In this paper, the inverse method is firstly introduced. A noise source model from an IC is proposed based on an array of dipoles. These dipole moments can be extracted from the near-field measurement in a scanning plane above the IC. Each dipole is modeled as an equivalent combined source consists of wire antennas and loop antennas. Then the radiation of IC in far-field region can be easily obtained. Finally, an example of physical IC is given to validate the approach.