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ABSTRACT A unified theory of near-field spiral scans is proposed in this work by introducing a sampling representation of the radiated electromagnetic field on a rotational surface from the knowledge of a nonredundant number of its samples on a spiral wrapping the surface. The obtained results are general, since they are valid for spirals wrapping on quite arbitrary rotational surfaces, and can be directly applied to the pattern reconstruction via near-field–far-field transformation techniques. Some numerical tests, assessing the accuracy of the technique and its stability with respect to random errors affecting the data, are reported with reference to the case of the helicoidal scan.
At the Institut Fresnel in Marseille (France), we created an original experimental setup in order to test antennas and carry out scattering measurements in both monostatic and bistatic configurations. The main advantage of this setup is, of course, the multipurpose feature. Two main mechanical systems are installed in a large anechoic chamber. The first system is a spherical positioning setup which allows measurements of antennas and scattered fields for both bi-dimensional (2D) and three-dimensional (3D) targets. This setup consists of two carriages moving on a circular vertical arch and a third carriage which follows a circular path on a horizontal plane. A transmitter and a receiver can be fixed on any of these three carriages. A fourth rotating stage in the center of the spherical setup fixes the angular position of the antenna under test or of the scattering target. The second system is a far-field positioner which allows the measurement antenna patterns and RCS. To illustrate our activities with this original setup, we first show measurements of a metamaterial antenna prototype and then some results of scattered fields obtained on 2D and 3D targets used in studies of electromagnetic direct and inverse problems.
The present paper introduces a new antenna design to be used in anechoic chambers. When measuring 3D patterns the receiving antenna in the anechoic chamber must be able to sense the two orthogonal components of the field that exist in the far field. This can be accomplished by mechanically rotating the source horn in the chamber. A better and faster approach is to use a dual polarized antenna and electronically switch between polarizations. This new design is a broadband (2-18GHz) antenna with dual polarization. The antenna is a ridged guide horn. The novel part is that the sides have been omitted. Numerical analysis and measurements show that this open-sided or open-boundary horn provides a better and more stable pattern behavior for the entire band of operation as well as good directivity for its compact design. The radiation and input parameters of the antenna are analyzed in this paper for the novel design as well as for some of the early prototypes to show some of the ill effects of bounded quadridge horn designs for broadband applications. Mechanically the antenna is built so that it can be mounted onto the shield of an anechoic room without compromising the shield integrity of the chamber.
ABSTRACT We are in the era of wireless communications and devices. The antennas that enable these technologies are electrically small and can be challenging to test and analyze. Yet, the industry is becoming more standardized, and so too are the tests and certifications being adopted to validate these antennas. These antennas must undergo “antenna measurements” to characterize such information as far-field patterns and gain. Additionally, hand-held devices, such as cell phones, must satisfy requirements of the Over-the-Air (OTA) performance tests as specified by the Cellular Telecommunication and Internet Association (CTIA). These tests require a measurement system that can accurately collect data on a spherical surface enclosing the AUT. This system also has to provide the appropriate data analysis capabilities and has to be constructed from dielectric materials to minimize reflections.
Radiation efficiency is an inherent property of an antenna that relates the net power accepted by an antenna to the total radiated power. It is especially useful for handset antennas where the radiation patterns are often of less use for comparing competing antennas. Radiation patterns though not as useful for direct comparisons, still provide one method by which efficiency can be calculated. To accurately calculate the efficiency from patterns, it becomes necessary to obtain multiple pattern measurements (cuts). A larger number of cuts whilst yielding more accurate efficiency results, significantly increase measurement time. Thus an antenna designer is often forced to trade off accuracy against measurement time since both quick and accurate measurements are desired. The focus of this paper is to quantify this trade off, in order to provide guidelines on the number of pattern measurements required for accurate efficiency results. Simulated and measured far-field radiation patterns are used and various numbers of cuts are utilized to quantify the loss in accuracy with a reduced number of cuts. The techniques outlined are geared primarily towards cellular handset antennas.
A hemi-spherical near-field test system with to be considered. This type of test system offers a added far-field capability is described. The facility has practical solution to the test problem in that combined been constructed for the characterization of automotive motion of a probe antenna and the object under test, antennas. The test system consists of an 11m tall allows for spherical data acquisition covering one half of dielectric gantry, a 6.5m diameter in-ground turntable and the spherical surface. The configuration also allowsa 28m-diameter radome enclosure. Special software integration of a conducting ground plane as well as a required to compensate for the reflectivity in the facility radome enclosure for weather protection andand the hemi-spherical truncation was developed and confidentiality. forms an integral part of this test system. The characteristics of this facility are described in this paper The characteristics of this newly developed and measured data is presented. facility are described in the following section of this paper.
The KRISS is in the process of completing the construction and installation of a planar near-field antenna test facility in the frequency range of 2 GHz to 50 GHz. This paper describes the planar near-field antenna test facility. Comparison of the far-field pattern, for verifying the antenna test facility, using a parabola antenna as artifact is also described. The patterns were measured by using the installed antenna test facility and a method developed by our group and showed good agreement.
In this paper two planar near-field scan plane reduction techniques are considered and results are presented. It is shown how truncation based on field intensity contours, instead of simple geometric truncation can in some cases improve the efficiency of the truncation process. Both techniques are applied to measured data sets and it is shown how these methods can be used to reduce data acquisition times while also assessing the impact of the total acquisition surface reduction on the far-field radiation pattern integrity.
This paper presents the results of a laboratory simulation of an outdoor telematic antenna test site that employs spherical near-field scanning to determine the far fields of telematic antennas mounted on vehicles.
We estimate uncertainties in the test antenna transmitting function due to uncertainties in the near- field measurements and in the probe receiving function.
It is well known that a microstrip transmission line can radiate if it is excited in its first higher order mode (with the fundamental or dominant mode suppressed). A new microstrip configuration is proposed that supports the first higher order mode while suppressing the fundamental mode. To quantify the leakage constants in the two cases for comparison purposes, several experimental means are considered to determine the source amplitude distribution from which the leakage constants may be deduced. First, an approximation to the source distribution is determined from the far field patterns themselves. Second, the source distribution is determined by carefully probing the near field. This paper uses these techniques to verify the performance of a new leaky wave antenna design.
The Geometrical Optics characteristics of single parabolic reflector compact range systems are presented in rules of thumb for amplitude taper, phase taper and cross polarization. This is illustrated on four different range configurations (two different focal lengths and two different offset angles). Also the influence of the feed system in regard to far field diagram and alignment is discussed for typical low and medium gain corrugated feeds. No diffraction effects are discussed in this paper. With the use of the rules of thumb, a fast and yet precise qualitative and quantitative analysis, optimization and trade off can be made for a compact range optimized for the available space as well as the application.
In this paper, we present an analysis of the impact of positioning errors on the performance of the GDAIS circular image-based near field-to-far field RCS transformation (CNFFFT). The analysis is part of our continuing investigation into the application of near fieldto-far field transformations to ground-based signature diagnostics. In particular, the analysis focuses on the errors associated with ground-to-ground, near-field, whole-body measurements where the radar moves on a nominally circular path around the target. Two types of positioning errors are considered: slowly-varying, long term drift and rapidly-varying, random perturbations about the nominal circular path. The analyses are conducted using simulated data from a target comprised of an array of generalized point scatterers which model both single and multiple interactions on the target. The performance of the CNFFFT was evaluated in terms of the angle sector cumulative RCS statistics. The analyses were performed as a function of frequency for varying amounts of position error, both with and without (approximate) motion compensation. As expected, the results show that the CNFFFT is significantly more sensitive to rapidly-varying position errors, but that acceptable performance can be achieved with motion compensation provided an accurate estimate of the errors is available.
An internal research and development project at the Georgia Tech Research Institute (GTRI) focused on cohering multiple apertures into a single distributed aperture. Cohered distributed aperture antenna patterns were collected on the GTRI far-field range for a 1.5 GHz bandwidth at X-band frequencies. Both 1-way and 2-way antenna patterns were measured, with the 1-way antenna pattern measurement requiring coherence on receive only and the 2-way antenna pattern measurement requiring coherence on transmit and receive. The resulting data were compared with the ideal angular resolution and power-aperture gain product improvements from a perfectly cohered distributed aperture, and the results are presented. As measurement techniques were developed for collecting 1-way and 2-way antenna pattern data, sources of potential errors in measurement collection and aperture coherence were identified, with potential methods of error mitigation outlined.
For enhancing the performance of existing near field antenna test facilities it is quite reasonable to use both conventional (the amplitude and phase measurements) and the phaseless measurements techniques during electrically scanning phased array antennas (PAA) testing. This simple yet critical approach helps to improve the quality of PAA alignment and testing reducing measurement errors and saving costs. In this way many difficulties related to precise phase measurements are overcome. Both simulation and measurement results will be presented to demonstrate the utility of such approach to PAA alignment and determination of its parameters. Comparison will be made between the PAA patterns for electrically scanned beams calculated using traditional near field - far field (NF/FF) transformations, the phaseless methods and the results obtained applying both measurement techniques.
This paper presents a novel variable width time gating technique, which is applied to planar and cylindrical near-field data in impulse time-domain antenna near-field measurements. Due to the changing distance between the probe and the antenna under test (AUT) in planar and cylindrical scans, the conventional fixed time gating technique causes problems to remove multiple reflections from the desired AUT response. It further limits the application of time-domain measurement to planar and cylindrical scans. The new variable width time gating technique provides a flexible way to solve these problems. Test results for both planar and cylindrical near-field measurements are presented. The difference of far-field patterns between time-domain and frequency-domain near-field measurements is noticeable. We also show the effects on the far field patterns due to fixed and variable time gating windows. We further conclude that the time-domain technique also works for planar and cylindrical near-field measurements by using variable width time gating technique.
This paper presents a novel variable width time gating technique, which is applied to planar and cylindrical near-field data in impulse time-domain antenna near-field measurements. Due to the changing distance between the probe and the antenna under test (AUT) in planar and cylindrical scans, the conventional fixed time gating technique causes problems to remove multiple reflections from the desired AUT response. It further limits the application of time-domain measurement to planar and cylindrical scans. The new variable width time gating technique provides a flexible way to solve these problems. Test results for both planar and cylindrical near-field measurements are presented. The difference of far-field patterns between time-domain and frequency-domain near-field measurements is noticeable. We also show the effects on the far field patterns due to fixed and variable time gating windows. We further conclude that the time-domain technique also works for planar and cylindrical near-field measurements by using variable width time gating technique.
This paper presents an evaluation of the suitability of the 65-foot range for the measurement of the far-field radiation characteristics of antennas located above a sea water half space. The 65-foot range corresponds to the measurement distance of the Overwater Antenna Measurement Facility (Arch) at the Naval Undersea Warfare Center (NUWC) Division, Newport, RI. Four antennas are investigated at the 200- to 400-MHz frequency range for antenna base heights ranging from 0 to 20 feet above sea water. The results presented are based on thin-wire model representations of the antennas using the Numerical Electromagnetics Code (NEC), version 4.1. The radiation parameters investigated are the directive gain, axial ratio, direction of maximum gain, and the location and depth of the first null above the horizon. For each antenna, plots of the differences of the computed radiation parameters at the 65-foot and far-field ranges are given as functions of frequency for various antenna base height above sea water. It is anticipated that the results presented in this paper may be helpful for determining at what frequencies and heights the NUWC Arch will provide accurate far-field measurements for a given type of antenna.
A problem of determination of an antenna phase center (PhC) usually is solved by different ways from a theoretical calculation to the near-field measurements of complex characteristics in the aperture of an antenna or the far-field measurements of the radiation-pattern phase. The present paper is devoted to a general technique of an antenna PhC determination by use of the known (or the measured) distribution of the complex characteristics in the antenna near zone or the phase pattern in the far zone. An algorithm of determination of the phase pattern evolute, based on the lowest moments of distribution, as well as a criterion for PhC existence, which is independent on the observation angle, are offered. A simple expression of PhC for an antenna with a quadratic phase distribution in the aperture is obtained. An error of PhC determination depending on both the error of observation angle and the error of measurement of the phase pattern is considered.
Since the early days of spherical near-field far-field transformations a recommendation for the necessary number of polar modes has been given by , being the wavenumber and or the radius of the minimum sphere. The almost explosive development in computer speed and storage capacity witnessed during the last two decades has made trans-formations of fields from antennas exceeding thou-sands of wavelengths feasible, and a closer investiga-tion of the above expression seems to be appropriate. An improved expression for the number of modes, N, related to the antenna size and the required accuracy will be developed. The impact of truncation of the modal expansion at a given level will be illustrated. This is especially important for measurements where noise is present, or where there is undesirable scatter-ing from objects.