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This paper describes the behavior of the antenna radiation pattern for different planar near-field measurement errors superimposed on the near-field data. The disturbed radiating near field is processed using multilevel plane wave based near-field far-field transformation to determine the far-field. Errors like scan area truncation, transverse and longitudinal position inaccuracy of measurement points, and irregular sample spacing are analyzed for an electrically large parabolic reflector at 40 GHz. The error behavior is then compared with the standard transformation technique employing 2D Fast Fourier Transform (FFT) using the same near-field data. In order to exclude the effect of any other measurement or environmental error, electric dipoles with appropriate magnitude profile and geometrical arrangement are used to model the test antenna.
This paper describes the behavior of the antenna radiation pattern for different planar near-field measurement errors superimposed on the near-field data. The disturbed radiating near field is processed using multilevel plane wave based near-field far-field transformation to determine the far-field. Errors like scan area truncation, transverse and longitudinal position inaccuracy of measurement points, and irregular sample spacing are analyzed for an electrically large parabolic reflector at 40 GHz. The error behavior is then compared with the standard transformation technique employing 2D Fast Fourier Transform (FFT) using the same near-field data. In order to exclude the effect of any other measurement or environmental error, electric dipoles with appropriate magnitude profile and geometrical arrangement are used to model the test antenna.
A low cost transportable short range Synthetic Aperture Radar (SAR) measurement system is constructed by placing a linear positioner on the bed of a truck. The radar system is based on a network analyzer and a pair of standard horn antennas. The SAR system gives a resolution of 0.3 m at X-band frequencies and 100 m measurement distance. By using the terrain the objects can be measured at depression angles up to at least 10. . The near field SAR images are processed using back projection algorithms. The system can be used to estimate camouflage efficacy in realistic environments. Flexible software based entirely on open source components is developed for the data processing, presentation and analysis of the SAR images. Results from the evaluation of two generic camouflage nets using reference targets in different backgrounds and SAR images of vehicles are presented.
A low cost transportable short range Synthetic Aperture Radar (SAR) measurement system is constructed by placing a linear positioner on the bed of a truck. The radar system is based on a network analyzer and a pair of standard horn antennas. The SAR system gives a resolution of 0.3 m at X-band frequencies and 100 m measurement distance. By using the terrain the objects can be measured at depression angles up to at least 10. . The near field SAR images are processed using back projection algorithms. The system can be used to estimate camouflage efficacy in realistic environments. Flexible software based entirely on open source components is developed for the data processing, presentation and analysis of the SAR images. Results from the evaluation of two generic camouflage nets using reference targets in different backgrounds and SAR images of vehicles are presented.
Large phased arrays have stringent beam-pointing accuracy requirements over their scan volume. Measuring the beam-pointing accuracy of a phased array with a planar near-field scanner is convenient but can lead to erroneous results if the near-field sampling grid is not well controlled. This paper describes numerical experiments that were carried out to assess the impact of various types of grid errors on the measurement of beam-pointing accuracy. The types of grid errors considered include skewing and curvature in the plane of the grid. The numerical experiments use infinitesimal dipoles as the radiating elements and assume an ideal probe. It is shown that beam-pointing errors induced by grid errors that can be described by an affine transformation can be estimated in closed form. For more complicated grid errors, the model is shown to be a useful tool in estimating their impact on measuring beam-pointing error. Finally, the amount of over-scan required for accurate beam-pointing measurements over a large scan volume is examined.
The radiation pattern of an antenna can be determined accurately by near-field measurement and transformation techniques. Low numerical complexity, full probe correction capabilities, and high accuracy of the transformed far-field pattern are important features of near-field transformation algorithms. The multilevel plane wave based near-field transformation algorithm achieves an efficient full probe correction by plane wave representations of antenna and field probe and realizes the low numerical complexity by hierarchical grouping of measurement points. Field translations are carried out to the boxes on the coarsest level and are further processed to the measurement points by disaggregation and anterpolation. Disaggregation is a simple phase shift of the plane waves and anterpolation reduces the sampling rate corresponding to the spectral content of the plane wave spectra on the various levels. The accuracy of the transformation is influenced by several variables where the number of buffer boxes between antenna and measurement point groups is crucial. A higher accuracy due to more buffer boxes can be achieved at the cost of increased computation time. Adaptive field translations structure the measurement setup such that individual groups are transformed with the required accuracy at lowest costs. A detailed investigation for a planar near-field measurement will be shown.
This paper validates the sub-reflectarray technique for main reflector antenna distortion compensation through simulations and measurements. First, axial defocusing of the feed creates spherical aberration distortion and it is corrected using sub-reflectarray by conjugate field matching method. Then, a ring-type distortion is created on the main reflector and it is also compensated using a similar approach. A hybrid HFSS/PO simulation approach was used for the design and analysis. Bipolar planar near-field measurements are performed to validate the compensation technique and back projection holography is used to locate the position of distortions and to study the effects of the distortion on the antenna performance.
We are developing a new-generation weather radar to observe and predict short-term weather phenomena like severe storms, gust and so on. Therefore, an active phased array antenna (APAA) with digital beam-forming (DBF) receivers could be used for the new-generation weather radar to reduce the observation time. In Toshiba Corporation, 33m x 16m vertical near-field antenna range including the digital instrumentation receivers have been working for multi-beam DBF antenna measurements. This near-field antenna range is used to evaluate the performance of an APAA. In this paper, we describe the characteristics of this new-generation weather radar and the APAA. And we demonstrate the antenna measurement set-up using the near-field antenna range and the measurement results of this antenna.
This paper compares 3 sets of far-field patterns of an S-Band Open Ended Waveguide (OEWG). The sources for the data are measurements from NPL, an EM-Model and the commonly used NIST analytical model. Both co-polarized (co-pol) and cross-polarized (x-pol) patterns are compared. Results indicate that accuracy improvements are possible by utilizing an EM-Model in certain applications. These applications as well as the pros and cons of doing this are discussed. Understanding the differences between these 3 independent sets of data enables near-field range engineers to better understand the directional dependence of probe correction accuracies over the majority of the forward hemisphere. Information and insight gained from this comparison, along with specific AUT requirements, better equips the near-field range user to address probe correction concerns and ultimately to determine if a calibrated probe solution is required for their unique testing scenario.
When specifying a Near Field scanner, intended to measure radiating systems under operational conditions, one of the requirements is the power flux density that the Near Field system and the absorbers on it have to with-stand. Today's trend is to use an EM-solver to calculate field intensities of (aperture) antennas. The advantage of these solvers is that they can handle any geometry but the disadvantages are that they can only handle limited dimensions and use approximations. Analytical solutions are not only more elegant and accurate but they also provide insight in the field behavior. For symmetrical cases, it is clear that the maximum field intensities will appear on the symmetry axis. The only (nearly identical) expressions in the literature are from Rudduck and Chen [1] and Yaghjian [2]. These analytical expressions describe the on-axis electrical field intensity of a circular aperture with uniform illumination. Rudduck and Chen have derived their equation via a Plane Wave Spectrum approach. Unfortunately, Yaghjian provided this version without reference or background about the derivation. It turns out that the expressions of [1,2] need a (minor) correction. Besides that, uniform illumination is not a very realistic case. This paper will also present an analytical expression for a tapered illumination. Graphs will be provided of the equation of [1,2], the corrected formula for the uniform illumination case and the new expression for the tapered illumination case.
This paper describes test methods and challenges for performing radio frequency (RF) characterization of a phased array antenna with element-level digital beamforming using planar near-field (PNF) and compact range technologies. The characterization of a digital array requires the synchronization of measurement equipment including positioner controllers, transmitters, and receivers. All hardware and software must remain synchronized with the array clock to achieve accurate amplitude and phase samples and ensure a coherent phase front. This synchronization is achieved through handshake triggers and communication protocols that are managed through external software. The acquisition of element-level data over large PNF scans presents unique challenges in data and post-processing that precipitate the need for optimization of array architecture as well as design of processing software. Advantages of the digital array architecture include being able to generate multiple receive beams from a single near-field scan for each frequency and the ability to compare multiple calibration methods efficiently using off-array processing.
It is no easy task to determine electromagnetic fields close to scattering objects. In some cases, it is required to measure the fields in shadow regions, or to find the effects of unwanted obstacles in the vicinity of an RF equipment system. We introduce a unique and rather simple way to obtain fields in areas inaccessible to measurement. The technique is based on the Field Mapping Algorithm (FMA), which determines fields in those regions where direct measurement is not feasible, from near-field measurements that are taken on an easily accessible surface. Verification of our FMA was carried out by analytic examples, by FDTD simulations, as well as by hardware measurements. For determining the fields close to scattering objects, three measurement test cases are given, with excellent results evident throughout.
Far field measurements of ground vehicle antennas in anechoic chambers often require the creation of a plane wave by near field hemispherical probing with associated mathematical transformations to the far field/plane wave result. Direct far field measurements can be done to save time when the frequency is low enough. This paper discusses a method of extending the frequency band where direct measurements can be done by synthesizing a plane wave using a small array of antennas. The use of an array to create a plane wave in an anechoic chamber usually results in errors due to the reflections from the walls of the chamber. The technique to be described in this paper is to model the wall reflections and the array antenna characteristics and to use optimization techniques to derive an antenna placement and power distribution scheme to optimize the plane wave. Several optimization techniques will be described and results from testing in a 1.2 meter long sub-scale chamber model will be shown. Improvements in the far field measurements will be discussed.
Highly accurate spherical near-field measurement systems require precise alignment of the probe antenna to the measurement surface. MI Technologies has designed and constructed a new spherical near field arch positioner with a 1.5 meter radius to support measurements requiring accurate knowledge of the probe phase center to within .0064 cm throughout its range of travel. To achieve this level of accuracy, several key design elements were considered. First, a highly robust mechanical design was considered and implemented. Second, a tracking laser interferometer system was included in the system for characterization of residual errors in the position of the probe. Third, a position control system was implemented that would automatically correct for the residual errors. The scanner includes a two position automated probe changer for automated measurements of multi-band antennas and a high accuracy azimuth axis. The azimuth axis includes an algorithm for correcting residual, repeatable positioning errors. This paper defines the spherical near-field system and relation of each axis to the global coordinate system, discusses their associated error sources and the effect on global positioning and presents achieved highly accurate results.
Highly accurate spherical near-field measurement systems require precise alignment of the probe antenna to the measurement surface. MI Technologies has designed and constructed a new spherical near field arch positioner with a 1.5 meter radius to support measurements requiring accurate knowledge of the probe phase center to within .0064 cm throughout its range of travel. To achieve this level of accuracy, several key design elements were considered. First, a highly robust mechanical design was considered and implemented. Second, a tracking laser interferometer system was included in the system for characterization of residual errors in the position of the probe. Third, a position control system was implemented that would automatically correct for the residual errors. The scanner includes a two position automated probe changer for automated measurements of multi-band antennas and a high accuracy azimuth axis. The azimuth axis includes an algorithm for correcting residual, repeatable positioning errors. This paper defines the spherical near-field system and relation of each axis to the global coordinate system, discusses their associated error sources and the effect on global positioning and presents achieved highly accurate results.
Recently, a significant effort from different research groups have been aimed at the problem of reconstructing the extreme near field radiated by an antenna from measured field data [1]–[8]. Among the different proposed solutions, the inverse source or equivalent current/source method (EQC) based on discretization of integral equations has attracted considerable attention due to a host of promising applications in antenna design and diagnostics. The integral equation approach constitutes a complement to more established tools such as plane-wave or spherical-wave expansion. At the expense of heavier computational burden this method offers a greater generality and flexibility since it allows reconstructing sources on arbitrary 3-D surfaces enclosing the antenna under test (AUT).
A comparison of antenna gain and radiation pattern for R-band (1.7 – 2.6 GHz) antennas has been performed between Korea Research Institute of Standards and Science (KRISS) and eight domestic participants including private companies and public institutes. Its purpose was to check equivalences between KRISS and participants in gain and radiation pattern measurements for antennas, particularly at R-band, to support antenna manufacturers and end users in Korea as a proficiency test program of the ‘Antenna Measurement Club’ of KRISS. This comparison uses three traveling standards (a general purpose antenna (pyramidal standard gain horn antenna), a fan-beam antenna (a sector antenna for mobile base stations), and a small antenna (a sleeve dipole antenna) and measurement parameters are the power gain and radiation pattern of the traveling standards. Gain comparison method, extrapolation method, and cylindrical near-field measurement method are used in this comparison.
ABSTRACT This work deals with the experimental validation of a direct near-field – far-field transformation with cylindrical scanning for electrically long antennas, which requires a minimum number of measurements. Such a transformation is based on a nonredundant sampling representation making use of a flexible source model-ling suitable to deal with electrically long antennas and allows the evaluation of the antenna far field directly from the acquired near-field data without interpolating them. The good agreement between the so recovered far-field patterns and those obtained via the classical cylindrical near-field – far-field transformation assesses the effectiveness of the approach.
Mathematical Absorber Reflection Suppression (MARS) has been used successfully to identify and extract range multi-path effects in a great many spherical [1, 2], cylindrical [3, 4], and planar [5, 6] near-field antenna measurement systems. This paper details a recent advance that enables the MARS measurement and post-processing technique to be used to correct antenna pattern data from far-field or compact antenna test ranges (CATRs) where only a single great circle pattern cut is taken. This paper provides an overview of the measurement and novel data transformation and post-processing chain that is utilised to efficiently correct far-field, frequency domain antenna pattern data. Preliminary results of range measurements that illustrate the success of the technique are presented and discussed.
Azimuthal mode (µ mode) truncation of a high-order probe pattern in probe-corrected spherical near-field antenna measurements is studied in this paper. The results of this paper provide rules for appropriate and sufficient µ-mode truncation for non-ideal first-order probes and odd-order probes with approximately 10dBi directivity. The presented azimuthal mode truncation rules allow minimizing the measurement burden of the probe pattern calibration and reducing the computational burden of the probe pattern correction.