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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.
Recent enhancements in military telecommunication systems for monitoring and tracking in low VHF range (30-80MHz) imply the use of specific antenna measurement facilities to characterize either the antenna alone or the antenna mounted on a supporting structure which can be heavy and bulky. The indoor Near-Field approach shows benefits in terms of compactness. However this approach involves issues due to high levels of reflectivity of the anechoic chamber, the antenna under test positioner and the measurement probe structure at these larges wavelengths. Studies and simulations of each contribution have been performed in a previous paper. The proposed paper focuses on the improvement of measurement results using post-processing techniques and associated uncertainty analysis of the mono-probe near-field system at the CNES. First the new 50-400 MHz dual polarized probe and the measurement system are briefly presented. Then the estimation of each error term is detailed providing a global error budget in order to appreciate the benefit of post-processing technique. All the considered errors terms are all of those included in the well-known 18 NIST terms. Each of them is evaluated using the most appropriated approaches (specific measurement, simulation).
Legacy methods for testing the performance of radome panels and finished radomes have always been in isolation from the system antenna, for many reasons. The legacy method of testing employed horn antennas at relatively close distances, a fixed-frequency signal source, and primitive receivers. More modern systems used much better receivers capable of measuring both phase and amplitude, and these gave way to automatic network analyzers. The network analyzer system also replaces the fixed-frequency source, because it has its own step-frequency source. The rest of the setup remains the same. A network analyzer can itself be calibrated, but that calibration cannot include the probe antennas, nor can it account for interactions, particularly at normal incidence. With increasing demands on performance, it is essential that the interaction effects of the probe antennas with the radome be removed. The micorwave integrated circuit industry has the identical problem. The circuit probes that are used to reach into the circuit assemblies have very small tips, and the internal elements to accomplish this size reduction make probe mataching difficult. Thus the probe parameters become embedded into the overall measured response. The circuit testing community has developed a process to de-embed these probes, yielding the S-parameters of the circuit under test in isolation from surroundings. This paper investigates a method for applying this closed-system technique to open-system testing, such as panel-measuremsnt tables, by using a secondary calibration technique that is adapted to open systems. This effectively extends the calibration of the analyzer system to encompass the probes, thus improving accuracy.
A technique is presented for determining the pattern of an antenna in the focused near-field from cylindrical near-field measurements. Although the same objective could be achieved by conventional near-field to far-field transformation followed by a back projection, the proposed technique has an intuitive appeal and is considerably simpler and faster. The focused near-field antenna pattern is obtained by applying Huygens’ principle, as embodied in the field equivalent principle, directly to near-field measurements and by including an “obliquity factor” to suppress backlobe radiation. The technique was experimentally verified by comparison with far-field patterns obtained by conventional cylindrical near-field to far-field transformation and by EM simulations. Excellent agreement in sidelobe levels and beamwidth was achieved. The technique was applied to the 25 in diameter reflector antenna of a harmonic radar operating at 5.8 GHz and 11.6 GHz. Since the operating range of this radar is less than 40 ft, the reflector is the near-field at both frequencies. By defocusing the reflector at the harmonic frequency the beamwidths and gains at both frequencies can be made the same. The defocusing is accomplished by exploiting the frequency dependent phase center displacement of a log-periodic feed.
There are many methods of aligning feeds on a dual cylindrical parabolic sub-reflector compact range. Presented in this paper is a laser tracker and Field probe method that was used to align the RF feed to the sub-reflectors. The laser tracker provides real time positional error measurements that are mapped and these results are used to fine tune the alignment of RF feed to the phase centers of the dual cylindrical parabolic sub-reflectors. Field probe test scans are performed to verify QZ performance of various alignment positions measured comparing scans of amplitude, phase and taper. The laser tracker alignment method provides an efficient and a highly accurate method to achieving precision alignment of the RF feed to the sub-reflector system installed into the dual reflector compact range. High accuracy antenna measurements in a compact range require precision alignment of the RF feed to the sub-reflectors phase center. The quality and size of the RF plane wave field of the quiet zone (QZ) performance is affected by the alignment of the RF feed and sub-reflector system combination. This alignment is accomplished through mechanical adjustments of the x-y-z axis RF feed positioning system. Measurements of both mechanical and electrical bore site is performed and compared across the full measurement spectrum to verify the compact antenna test range (CATR) system positioning accuracy.
Experimental measurement plays a key role for technology maturation in an R&D environment. In this paper we highlight the versatility of a new compact range at the Air Force Research Laboratory (AFRL), Sensors Directorate. In its first year of operation, the OneRY Range supported a wide variety of projects ranging from electrically small antennas to 20’ structures, spanning frequencies of 400 MHz to 45 GHz, and involving applications covering land, airborne, and space-based platforms. Here we present measured results from three different antenna development efforts for the Air Force. The first effort involves a UHF meta-material inspired antenna developed for an airborne application. In addition to successfully demonstrating relatively low frequency capability for a compact range, this effort met the challenge to measure antenna patterns from a physically large target. Results from OneRY are compared to those collected from a tapered chamber. Next we show experimental measurement of digital beam forming (DBF) in a large conformal phased array antenna operating at L and S bands. The DBF experimental testing is part of a follow-on effort to an Advance Technology Demonstration conformal array supporting satellite tracking, telemetry and command (TT&C). Finally, we present results from a “quick look” investigation into the operability of a COTS antenna system matched to a third party radome. The project supports airborne satellite communications at K, Ka, and Q bands. Performance of a high frequency extension (18-50 GHz) to the compact range is examined to include an inter-range comparison to planar near-field measurements. A description of the OneRY Indoor Range is also provided.
The outdoor range at the U. S. Army’s Electronic Proving Ground Antenna Test Facility features a large reflector in order to facilitate radar cross-section and antenna performance evaluation with large targets. Constructed during the late 1980s and early 1990s, this range features a 67-foot diameter reflector to satisfy quiet zone size specifications. The reflector is composed of 138 individual panels with nominal panel separation of 0.06 inches. This research investigates the impact of these gaps between reflector panels on the field received at the quiet zone. GTRI’s physical optics computational code was used to analyze the existing range design at the frequencies of interest, from C- through Ka-band, taking into account edge diffraction from the panels. In research presented at AMTA 2013, a range modification of the ground between the range source antenna and the reflector was performed to minimize ground reflections. This range modification has been incorporated with current research to provide quiet zone field analysis which includes reflector gaps as well as ground reflections.
A popular method for microwave characterization of materials is the free-space focused beam technique, which uses lenses or shaped reflectors to focus energy onto a confined region of a material specimen. In the 2-18 GHz band, 60 cm diameter lenses are typically spaced 30 to 90 cm from the specimen under test to form a Gaussian focused beam with plane-wave like characteristics at the focal point. This method has proved popular because of its accuracy and flexibility. Another free-space measurement technique that has been employed by some is the use of dielectrically loaded antennas that are placed in close proximity to a specimen. In this alternate technique, the dielectrically loaded antennas are smaller than lenses, making the hardware more compact and lower cost, however this is done at the expense of potentially reduced accuracy. This paper directly compares a standard laboratory focused beam system to a measurement system based on some recently developed RF spot probes. The spot probes are specially designed antennas that are encapsulated in a dielectric and optimized to provide a small illumination spot 3 to 8 cm in front of the probe. Experimental measurements of several dielectric, magnetic, and resistive specimens were measured by both systems for direct comparison. With these data, uncertainty analysis comparisons were made for both fixtures to establish measurement limits and capability differences between the two methods. Understanding these uncertainties and measurement limits are key to implementing compact spot probes in a manufacturing setting for quality assurance purposes.
Although highly accurate relative position data can be achieved using laser tracking systems which are suitable for millimeter wave antenna characterization, a considerable gap exists in the ability to absolutely align antennas to laser tracker target coordinate systems. In particular this scenario arises in millimeter wave near-field measurements where probe antenna aperture dimensions are on the order of a millimeter, and the position of its origin must be known to better than 1/20th of a wavelength, and orientation known to fractions of a degree. The fragile nature and dimensions of such antenna negate the use of coordinated metrology measurement systems and larger touch probes typically used for accurate spatial characterization. The Antenna Metrology Laboratory at NIST in Boulder, Colorado is developing a new machine vision based technique for measuring the absolute position of small (~1 mm) millimeter wave antenna apertures relative to a laser tracker target coordinate system. A synergy with existing laser tracking systems, this approach will provide a non-contact method for determining the absolute position and orientation coordinate frame of the probe antenna aperture in all six degrees of freedom to within 30-60 microns. This alignment system technique is demonstrated using the CROMMA Facility at NIST in Boulder, CO.
The development of the Configurable Robotic Millimeter-Wave Antenna facility (CROMMA) by the antenna metrology lab at the National Institute of Standards and Technology in Boulder Colorado has brought together several important aspects of 6-degree-of-freedom robotic motion, positioning and spatial metrology useful for high frequency antenna characterization. In particular, the ability to define a unified coordinated metrology space, which includes all the motion components of the system is at the heart of this facility. We present the details of integrating robotics that have well defined kinematic models, advanced spatial metrology techniques, and millimeter wave components which make up the CROMMA facility. From this, a high level of precision, accuracy, and traceability that is requisite for performing high frequency near-field antenna pattern measurements can be achieved. Emphasis is placed on the ability to precisely characterize and model the movement patterns of the robot positioners, and probe and test antenna apertures using state-of-the-art full 6-degree-of-freedom spatial metrology, while being able to manipulate this information in a unified measurement space. The advantages of using a unified coordinated metrology space as they pertain to complex antenna alignments, scan geometry, repeatability analysis, traceability, and uncertainty analysis will be discussed. In addition we will also discuss how the high level of positioning, and orientation knowledge obtainable with the CROMMA facility can enable the implementation of sophisticated near-field position correction algorithms and precisely configurable scan geometries.
In the near future, we will begin adorning our bodies with wearable devices, and the ubiquitous computing society will dawn. Personal area network (PAN), which uses the human body as a transmission channel, has been proposed by T. G. Zimmerman as a solution for networking these personal devices. The social concern regarding PAN's use for biomedical engineering has been growing due to Japan's low birthrate and longevity. ?Studies have focused on developing PAN applications, such as real-time healthcare sensing devices, following the trend of medicine-engineering cooperation. Since applications are still in their initial phase, a trial-and-error method is applied to device development. There are still many opaque areas regarding a transmission mechanism. ?So far, we have clarified that the electromagnetic wave generated from a 10 MHz PAN device propagates through the surface of the human body. If the frequency band of the surface wave, instead of radiation, becomes clear in air, it excels in privacy, and we can expect lower energy consumption. Transmission efficiency can also be expected to increase due to the adoption of the electrode structure, which excites a surface wave. ?In this paper, we clarify the propagation characteristics of the surface wave and advantageous frequency band for PAN. First, we constructed an experimental device like the Fabry-Perot resonator using the periodic structure of Yagi-Uda antenna directors with reflectors in both ends for the measurement of surface waves. Next, "solid phantom," which is equivalent to biological tissue, was installed in the device. Moreover, in order to demonstrate measurement validity, we conducted numerical analysis using the finite-difference time-domain method.
It is well known that a field probe acts as a filter for the measured antenna under test (AUT) fields, whose influence can be either described in spatial or in spectral domain. Directive probes, for instance, serve to filter out signals that originate far away from the boresight axis. However, there are several drawbacks to the use of such directive probes including the possibility of multiple reflections and probe nulls. This contribution discusses the application of beamforming techniques to suppress unwanted echo signals in planar near-field antenna measurements. The AUT is measured with a small probe antenna such as is normally used for such measurements. Neighboring measurement signals are thereafter combined in a moving average manner in order to generate the signal as would be measured by a probe array. Successive filter lengths, such as 3x3, 5x5, etc., are utilized such that the valid angle is preserved without extending the measurement plane. The generated near-field signals are then transformed using a flexible plane wave based near-field far-field transformation algorithm. Probe correction does not reverse the reduction in multipath signals achieved by the use of a directive probe or beamforming since sources are assumed only within the minimum sphere enclosing the AUT. Results are presented for simulated data with substantially improved results of the far-field pattern of the AUT.