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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.
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.
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.
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.
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.
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.
In classical probe-corrected spherical near-field measurements, one source of measurement errors, not often given sufficient consideration is the probe [1-3]. Standard near-field to far-field (NFFF) transformation software applies probe correction with the assumption that the probe pattern behaves with a µ=±1 azimuthal dependence. In reality, any physically-realizable probe is just an approximation to this ideal case. Probe excitation errors, finite manufacturing tolerances, and probe interaction with the mounting interface and absorbers are examples of errors that can lead to presence of higher-order spherical modes in the probe pattern [4-5]. This in turn leads to errors in the measurements. Although probe correction techniques for higher-order probes are feasible [6], they are highly demanding in terms of implementation complexity as well as in terms of calibration and post-processing time. Thus, probes with high azimuthal mode purity are generally preferred. Dual polarized probes for modern high-accuracy measurement systems have strict requirements in terms of pattern shape, polarization purity, return loss and port-to-port isolation. As a desired feature of modern probes the useable bandwidth should exceed that of the antenna under test so that probe mounting and alignment is performed only once during a measurement campaign. Consequently, the probe design is a trade-off between performance requirements and usable bandwidth. High performance, dual polarized probe rely on balanced feeding in the orthomode junction (OMJ) to achieve good performance on a wide, more than octave, bandwidth [5-7]. Excitation errors of the balanced feeding must be minimized to reduce the excitation of higher order spherical modes. Balanced feeding on a wide bandwidth has been mainly realized with external feeding network and the finite accuracy of the external components constitutes the upper limits on the achievable performance. In this paper, a new OMJ designed entirely in waveguide and capable of covering more than an octave bandwidth will be presented. The excitation purity of the balanced feeding is limited only by the manufacturing accuracy of the waveguide. The paper presents the waveguide based OMJ concept including probe design covering the bandwidth from 18-40GHz using a single and dual apertures. The experimental validation is completed with measurements on the dual aperture probe in the DTU-ESA Spherical Near-Field facility in Denmark. References: [1]Standard Test Procedures for Antennas, IEEE Std.149-1979 [2]Recommended Practice for Near-Field Antenna Measurements, IEEE 1720-2012 [3]J. E. Hansen (ed.), Spherical Near-Field Antenna Measurements, Peter Peregrinus Ltd., on behalf of IEE, London, UK, 1988 [4]L. J. Foged, A. Giacomini, R. Morbidini, J. Estrada, S. Pivnenko, “Design and experimental verification of Ka-band Near Field probe based on wideband OMJ with minimum higher order spherical mode content”, 34th Annual Symposium of the Antenna Measurement Techniques Association, AMTA, October 2012, Seattle, Washington, USA [5]L. J. Foged, A. Giacomini, R. Morbidini, “Probe performance limitation due to excitation errors in external beam forming network”, 33rd Annual Symposium of the Antenna Measurement Techniques Association, AMTA, October 2011, Englewood, Colorado, USA [6]T. Laitinen, S. Pivnenko, J. M. Nielsen, and O. Breinbjerg, “Theory and practice of the FFT/matrix inversion technique for probe-corrected spherical near- eld antenna measurements with high-order probes,” IEEE Trans. Antennas Propag., vol. 58, no. 8, pp. 2623–2631, Aug. 2010. [7]L. J. Foged, A. Giacomini, R. Morbidini, "Wideband dual polarised open-ended waveguide probe", AMTA 2010 Symposium, October, Atlanta, Georgia, USA. [8]L. J. Foged, A. Giacomini, R. Morbidini, “ “Wideband Field Probes for Advanced Measurement Applications”, IEEE COMCAS 2011, 3rd International Conference on Microwaves, Communications, Antennas and Electronic Systems, Tel-Aviv, Israel, November 7-9, 2011.
Broad band, dual polarized probes are becoming increasingly popular options for use in near-field antenna measurements. These probes allow one to reduce cost and setup time by replacing several narrowband probes like open-ended waveguides (OEWG) with a single device covering multiple waveguide bands. These probes are also ideal for production environments, where chamber throughput should be maximized. Unfortunately, these broadband probes have some disadvantages that must be quantified and corrected for in order to make them viable for high accuracy near-field measurements. Most of these broadband probes do not have low cross polarization levels across their full operating bandwidths and may also have undesirable artifacts in the main component of their patterns at some frequencies. Both of these factors will result in measurement errors when used as probes. Furthermore, the use of a dual port RF switch adds an additional level of uncertainty in the form of port-to-port channel balance errors that must be accounted for. This paper will describe procedures to calibrate the pattern and polarization properties of broad band, dual polarized probes with an emphasis on a newly developed polarization correction algorithm. A simple procedure to measure and correct for amplitude and phase imbalance entering the two ports of the near-field probe will also be presented. Measured results of the three calibration procedures (pattern, polarization, channel balance) will be presented for a dual-polarized, broad band quad-ridged horn antenna. Once calibrated, this probe was used to measure a standard gain horn (SGH) and will be compared to baseline measurements acquired using a good polarization standard open-ended waveguide (OEWG). Results with and without the various calibration algorithms will illustrate the advantage to using all three routines to yield high accuracy far-field pattern data.
Indoor RCS measurement facilities are usually dedicated to the characterization of only one azimuth cut and one elevation cut of the full spherical RCS target pattern. In order to perform more complete characterizations, a spherical experimental layout has been developed at CEA for indoor Near Field monostatic RCS assessment. This experimental layout is composed of a 4 meters radius motorized rotating arch (horizontal axis) holding the measurement antennas while the target is located on a mast (polystyrene or Plexiglas) mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allows full 3D near field monostatic RCS characterization. This paper investigates the influence of the material of the mast supporting the target under test. Across several measurement steps, we compare different RCS measurement results of canonical targets in order to eliminate the unwanted RCS measurement contribution due to the mast. The aim is to find out the mast which disturbs the least the RCS of the target under test but still compatible with the measurement facility ARCHE 3D. All these measurements are also compared to Near Field and Far Field calculations taking into account the material of the supporting mast.
The synthesis of a specific field distribution in a certain volume with a given set of sources is an issue which arises in acoustics as well as in electromagnetics. Field Synthesis is of increasing interest for over the air (OTA) testing of multiple input multiple output (MIMO) based communication devices as arbitrary multipath communication channels can be simulated synthesizing the corresponding field distribution around the device under test (DUT). Plane-wave Field Synthesis methods have already been applied to improve the quality and extents of the quiet zone region of compact antenna test ranges (CATR). Furthermore, by synthesizing a plane wave field in a test region for an antenna under test (AUT), using an array of probe antennas in its near-field region, near-field far-field transformations (NFFFT) can be performed. Since there exists a variety of important applications for electromagnetic Field Synthesis, a Field Synthesis approach with high flexibility and low computational complexity is presented in this contribution. Usually, depending on the application, a single moving probe antenna or an array of probe antennas is used to synthesize a desired field distribution in the test zone volume where the DUT will be placed. The challenge is to determine appropriate excitation signals for the individual probe antennas. For that purpose an equation system is iteratively solved which arises from the boundary condition for the tangential field components on the surface of the test volume. As a consequence of the uniqueness theorem, equality of the desired and synthesized tangential field components induces that the desired and synthesized field distribution are identical in the source free test volume. Field testing on the surface of the test volume is performed by vector testing functions defined on a triangular mesh of the test zone surface enabling field synthesis in arbitrarily shaped test volumes. For accelerated evaluation of the coupling between probe antennas and vector testing functions, principles of the fast multipole method (FMM) are adopted. The implied plane wave expansions enables to incorporate the radiation characteristic of the probe antenna sources just by directly employing its plane wave spectrum representation which is nothing else but its far-field pattern. Additionally, the multilevel approach minimizes the number of translation operations between source and receiver boxes organized in a hierarchical oct-tree. Altogether the approach is applicable to arbitrarily shaped test volumes and arbitrarily arranged probe antennas and still shows a linearithmic complexity. In this contribution, detailed insight in the Field Synthesis method is given. Results for synthesized field distributions for arbitrarily shaped test volumes are presented. Finally the application of plane-wave Field Synthesis to NFFFT is shown for synthetic as well as for real near-field antenna measurement data.
Historically, the inverse synthetic aperture radar (ISAR) reflectivity assumption has been used in the implementation of Image-Based Near Field-to-Far Field Transformations (IB-NFFFT) to estimate monostatic far field radar cross-sections (RCS) from monostatic near field radar measurements. The ISAR assumption states that all target scattering occurs at the location of the incident field excitations, i.e., the target is composed entirely of non-interacting localized scatters. Certain non-localized scattering phenomenon cannot be effectively handled by the IB-NFFFT approach with the ISAR assumption. Here we have used the adaptive Gaussian representation, which is a joint time-frequency decomposition technique, to coherently decompose near field measured data into two subsets of scattering features: one subset of localized scatterers and the other of non-localized scatterers. The localized scattering features are processed through the IB-NFFFT as typical, which includes compensating for the R4 fall-off present in the near field measured data. The non-localized scattering features, more appropriately scaled, are then coherently added back in to the post-NFFFT localized scattering phase history. Although this does not properly transform the non-localized scattering features into the far field, it does avoid the over-estimation error associated with improperly compensating distributed non-localized scattering features by a R4 power fall off based strictly on downrange position.
Historically, the inverse synthetic aperture radar (ISAR) reflectivity assumption has been used in the implementation of Image-Based Near Field-to-Far Field Transformations (IB-NFFFT) to estimate monostatic far field radar cross-sections (RCS) from monostatic near field radar measurements. The ISAR assumption states that all target scattering occurs at the location of the incident field excitations, i.e., the target is composed entirely of non-interacting localized scatters. Certain non-localized scattering phenomenon cannot be effectively handled by the IB-NFFFT approach with the ISAR assumption. Here we have used the adaptive Gaussian representation, which is a joint time-frequency decomposition technique, to coherently decompose near field measured data into two subsets of scattering features: one subset of localized scatterers and the other of non-localized scatterers. The localized scattering features are processed through the IB-NFFFT as typical, which includes compensating for the R4 fall-off present in the near field measured data. The non-localized scattering features, more appropriately scaled, are then coherently added back in to the post-NFFFT localized scattering phase history. Although this does not properly transform the non-localized scattering features into the far field, it does avoid the over-estimation error associated with improperly compensating distributed non-localized scattering features by a R4 power fall off based strictly on downrange position.
Abstract—It has been shown that it is possible to get a good estimation of the location of the largest centers of reflection causing ripple in the quiet zone using spherical near-field scanning of the quiet zone in combination with back projection to far-field. This method however, suffers from poor resolution at lower frequencies making it hard to distinguish small contributions from the main beam if they are closely spaced. For this purpose the CLEAN algorithm has been adapted and is presented here.
Abstract—The measurement geometry and data processing techniques employed in spherical near-field (SNF) antenna measurements naturally quantify the directivity of an antenna under test. Computing antenna gain from these measurements requires additional information and processing. Equations that can be used to calculate the magnitude of antenna gain from spherical near-field measurements are provided in seminal SNF references, but equations that describe how to calculate the complex gain voltage of an antenna with spherical near-field methods have been largely absent in the literature. This paper presents equations that may be used to calculate the complex gain voltage of an antenna using the gain substitution method in a spherical near-field test range. The equations are presented in a more generalized format than previously seen, and will show how to use a combination of data collected in the near-field with data transformed to the far-field to calculate the gain voltage. Practical examples are provided for determining gain voltage using a single measurement set-up or multiple measurement set-ups, including a method to calculate gain voltage of each port of a multi-port antenna requiring only a single full sphere measurement of the standard gain antenna.
Abstract— In order to achieve precise antenna pattern measurement in mm-wave frequency region, we propose a cylindrical near-field antenna measurement system using photomixing technique with UTC-PD. Due to this system, we can use an optical fiber as the transmission line of mm-wave signal and downsize the mm-wave signal source. Accordingly, we can achieve flexible cable movement and suppress the disturbance from the waveguide components. In this paper, we will show the measured near-field distribution on cylindrical coordinate by the proposed system and calculated far-field antenna pattern of standard gain horn antenna in W-band.
Abstract— This paper presents an original way for the design simulation, implementation, and measurement of a multiband flexible textile antenna. The aim is to realize an antenna with a dipolar radiation at several resonance frequencies. The radiating element is a monopole antenna. This antenna naturally exhibits a dipole and a quadripole radiation pattern for the first and second resonance frequency respectively. This behavior is due to the current distribution on the antenna. To constrain the second mode to change into a dipolar radiation pattern, two decorrelated and non-radiating parasitic elements are added to the antenna. At this second resonance frequency, the current distribution is different from the one of the quadripolar mode by the parasitic elements. The dimensions of these parasitic elements are defined by electromagnetic simulations and measurements. To validate this method, the monopole antenna is studied. The radiating element of the antenna is sewn on the textile flexible substrate. This substrate was previously characterized in terms of relative permittivity and losses. The near-field magnetic field and the far-field radiation pattern are studied in simulations and measurements.
Abstract—Four arm Log-Periodic (LP) antennas are frequency independent antennas that are capable of producing dual circular polarizations from the same aperture and over the same bandwidth making them more versatile than commonly used spiral antennas. In this paper we present a four arm LP that is capable of being a high power radiator. Each pair of arms of the LP is fed with a microstrip line that functions as both an impedance transformer and a 180° balun, thereby greatly simplifying the required beamformer. The antenna is tested successfully up to 500W of input CW power. Post high power characterizations of the antenna (far-field gain, radiation patterns, and VSWR) for linear polarization are presented and the stable high power performance of the antenna is demonstrated. With an appropriate beamformer, good quality circular polarization can be expected. Presented results should pave the way for use of the LP in relevant wideband high power applications.
Abstract — Nearfield Systems Inc. (NSI) has been contracted by the Department of Electrical and Computer Engineering of the University of Waterloo to install a unique antenna test system with multiple configurations allowing it to characterize a wide variety of antenna types over a very wide bandwidth. The system employs a total of 10 positional axes to allow near-field and far-field testing in various modes of operation with great flexibility. A 4 m x 4 m planar near-field (PNF) scanner is used for testing directive antennas operating at frequencies up to 110 GHz with laser interferometer position feedback providing dynamic probe position correction. The PNF’s Y-axis can also be used for cylindrical near-field (CNF) testing applications when paired with a floor mounted azimuth rotation stage. A single phi-over-theta positioner permits both spherical near-field (SNF) testing from L-band to W-band and far-field testing down to 0.2 GHz. This positioner is installed on a translation stage allowing 1.8 m of Z-axis travel to adjust the probe-to-AUT separation. In addition, a theta-over-phi swing arm SNF system is available for testing large, gravitationally sensitive antennas that may be easily installed on a floor mounted rotation stage. In order to ensure system and personnel safety, a complex interlock system was designed to reduce the risk of mechanical interference and ease the transition from one configuration to another. The system installation and validation was completed in March 2013. We believe that this facility is unique in that it encompasses all commonly used near-field configurations within one chamber. It therefore provides a perfect environment for the training of young engineers and could potentially form the baseline of future academic test facilities. This paper will outline the technical specifications of the scanner and discuss the recommended applications for each configuration. It will also describe the details of the safety interlock system.
Abstract -We propose a method of utilizing near-field spherical measurements so as to obtain the back lobes of high gain antennas without sacrificing the accuracy of the far-field, high-gain main lobe prediction. While a spherical scan is perfectly adequate to gauge the relatively broad back lobes, it is in general inadequate to capture the required details of a sharp forward peak. We overcome this difficulty through recourse to our Field Mapping Algorithm (FMA), which latter allows us to assemble planar near-field data based upon the spherical measurements actually acquired. In particular, planar data of this sort on the forward, main-lobe side offers the standard route to predicting the desired, high-gain, far-field pattern. Our spherical-to-planar FMA near-field data manufacture showed excellent agreement with direct planar near-field measurements for a slot array antenna, each one of them, naturally, underlying a common, far-field, high-gain pattern.
This paper will describe newly developed mechanical and electrical alignment techniques for use with plane-polar near-field test systems. A simulation of common plane-polar alignment errors will illustrate, and quantify, the alignment accuracy tolerances required to yield high quality far-field data, as well as bounding the impact of highly repeatable systematic alignment errors. The new plane-polar electrical alignment technique comprises an adaptation of the existing, widely used, spherical near-field electrical alignment procedure [8] and can be used on small, and large, plane-polar near-field antenna test systems.