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Abstract—The 3D reconstruction algorithm of DIATOOL is applied to the prototype feed array of the BIOMASS synthetic aperture radar, recently measured at the DTU-ESA Spherical Near-Field Antenna Test Facility in Denmark. Careful analysis of the measured feed array data had shown that the test support frame of the array had a significant influence on the measured feed pattern. The 3D reconstruction and further post-processing is therefore applied both to the feed array measured data, and a set of simulated data generated by the GRASP software which replicate the series of measurements. The results of the diagnostics and the corresponding improvement of the feed array field obtained by removal of the undesired effect of the frame are presented and discussed.
Abstract—This paper describes the approach of solving the electromagnetic scattered field of semicircular array using numerical method (MoM). Considering the variable number of elements, uniform radius of element, element spacing, azimuth plane as inputs of the numerical model and distributed complex current coefficients, scattered E-field are extracted as the outputs. The desired input and output to the artificial neural network are pattern values and number of elements respectively. The purpose of applying neural network is to change from lengthy analysis and design cycles required to develop high performance systems to very short product development times. The work allows the designer to achieve any desired values of pattern without requiring the usage of more elements. The generated data is divided in to training and test sets, for observing the error behavior with the progress of training. It is proved that the network gives a high success rate.
Abstract— Attempts to produce robust, objective, and quantitative measures of similarity between antenna pattern data sets using statistical methods have been widely reported in the open literature [1, 2]. Hitherto, such techniques have primarily been restricted to the purposes of comparing two or more images as a means in itself. However, no measurement can be considered to be completely free from error, and as such each data set inevitably contains an associated uncertainty. Therefore, in contrast to previous work, this paper discusses and extends some commonly used comparison techniques to take account of the finite, non-zero, measurement uncertainties that complicate the comparison process. Results are presented that illustrate the effectiveness of the comparison method and conclusions drawn.
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.
Abstract— This paper presents a two-layer mushroom-like reactive impedance surface (RIS) and patch antenna miniaturization with potential application in matel-backed antennas. RIS, known as meta-substrate, has shown the ability to miniaturize printed antennas with omni-directional radiation pattern, when served as the substrate for the antenna [11]. However, the area of conventional RIS substrate usually has to much larger than that of miniaturized antenna, since the cell’s dimension is comparable with the antenna, even using a high dielectric constant. Here an RIS with very small unit cell dimensions (cell area reduction by 95% compared to traditional RIS) is proposed and utilized to design a miniaturized antenna over the RIS substrate with the same size as the antenna itself. A microstrip transmission line over the RIS substrate model is studied and shown to have a high propagation constant near the resonant frequencies of the RIS. This model is used to predict the much reduced resonant frequency of patch antennas over the RIS. Applying the two-layer RIS substrate and an optimized miniaturized patch antenna topology, several UHF band patch antennas working around 400MHz have been designed and fabricated. Using this approach a miniaturized antenna with dimensions .0/11.4× .0/11.4 × .0/74, including the RIS substrate is developed.
This paper will discuss a highly customizable and integrated waveform generator (WFG) subsystem used to coordinate the phased array test process. The WFG subsystem is an automated digital pattern generator that orchestrates the command and triggering interface between the NSI measurement system and a phased array beam steering computer. The WFG subsystem is controlled directly by the NSI 2000 software and allows the test designer to select and generate a sequence of up to sixteen unique synchronized timing waveforms. Test scenarios, results and data for the WFG subsystem will be presented along with plots showing the key timing characteristics of the system.
Abstract—In this paper, a bespoke, fully automated anechoic chamber is discussed and the positioner effects on measurements of antennas are investigated. Antenna measurements performed in this robust anechoic chamber are undertaken in two parts namely; acquisition and analysis, with the aid of low cost positioner hardware and low level software language. In order to get a measure of validation of our measuring system only the important parts of the chamber have been modelled and measurements carried out using a balanced sleeved dipole and a microstrip patch antenna, which have well-known characteristics. It was noticed from the results that the positioner, exaggerates the performance of some antennas particularly small antennas without a ground plane at certain distances and frequencies. The positioner has a tendency to reflect energy, and distort radiation patterns; hence, it was important to ensure that such antennas are placed at an appropriate distance away from the positioner. The comparison between the simulated and measured efficiency of a balanced sleeved dipole is good. The predicted and measured peak efficiency at 2.49 GHz was 95% and 94% respectively. It was also observed that the variability in efficiency measurements was less than 3% for measurements with different angular resolutions on different days.
Radar sensor working at 76-77GHz band, because of its long detection range, high resolution and excellent performance in different weather and illumination conditions, has been used to develop on-road pedestrian collision avoidance system. Therefore, studying the pedestrian radar scattering features is important to develop reliable on-road pedestrian detection algorithm. In this paper, we first discuss the measurement setup requirement at 76-77GHz to obtain reliable radar cross section (RCS) data of human subjects. Then the RCS pattern of human subjects with different postures and different body features are measured and studied. The observed radar features could be further developed into stable radar signatures to improve the pedestrian identification algorithm.
The Fast Irregular Antenna Field Transformation Algorithm (FIAFTA) determines the equivalent sources of an antenna under test (AUT) from arbitrarily located sampling points of the antenna field. The application of Fast Multipole Method (FMM) principles to the formulation of the forward operator shows that the influence of the measurement probe is fully corrected based on its far-field radiation pattern. For antenna diagnostic purposes, equivalent surface current densities represent the unknown equivalent AUT sources. However, the FMM gives the possibility to settle the unknowns of the inverse problem in the ^k-space domain. The expansion of the appearing plane wave spectra in spherical harmonics leads to a compact representation of the equivalent plane wave sources. The forward operator is evaluated in a multilevel fashion similar to the Multilevel Fast Multipole Method (MLFMM). This enables to incorporate a priori knowledge about the geometry of the AUT in the antenna model by placing nonempty FMM boxes where sources are assumed.
There are several applications in which knowledge of the location of the phase center of an antenna, and its twodimensional variation, is an important feature of its use. A simple example occurs when a broad-beam antenna is used as a feed for a reflector, where the center of the spherical phase fronts should always lie at the focal point of the paraboloidal surface. Here, the ability to determine the phase center of the feed from knowledge of its far-field phase/amplitude pattern is critical to the reflector's design. Previously published methods process a single cut of data at a time, yielding 2D lateral and longitudinal phase-center offsets. Eand H-plane cuts are thus processed separately, and will, in general, yield different answers for the longitudinal offset. The technique presented here can process either one line cut at a time or a full Theta-Phi raster. In addition, multiple frequencies can be processed to determine the average 3D phase-center offset. The technique can merely report the phase-center location, or it can also adjust the measured phases to relocate the origin to the computed phase center. Example results from measured data on multiple antenna types are presented.
Compact range measurement facilities have been used successfully for many years to characterize antenna performance as well as radar signature. This paper investigates strategies for improving compact range measurement accuracy by mitigating errors associated with ground reflections inherent in most range designs. A methodology is developed for strategically modifying, or patterning, the surface between the range source antenna and the reflector to reduce error terms, thereby increasing measurement accuracy. Candidate patterns were evaluated using a full-wave computational finite-difference time-domain (FDTD) model at VHF/UHF frequencies to determine baseline performance and develop trade rules for more advanced designs. Physical optics (PO) models were used to analyze the final design at the frequencies of interest.
Multi Input Multi Output (MIMO) antenna systems are needed to meet the increasing demands of users in wireless systems. MIMO technology has been used to improve the capacity of wireless systems; however, designers have faced challenges to reduce antenna-size and increase the isolation between the antennas in MIMO systems. In this paper, a compact MIMO antenna array platform is proposed for LTE MIMO and Handset applications. The proposed array was designed to operate at the 2.6GHz Long-Term Evolution (LTE) band for wireless communication systems. The proposed array consists of four compact patch antennas on a dielectric substrate with total dimension of 12.5x6.25x1.27mm3. Modification of the ground plane along with the systematic placement and orientation of the antenna elements on top of the substrate play a key role to reduce mutual coupling, which normally degrades the performance of MIMO antenna arrays. The performance of this MIMO antenna array has been evaluated through simulations and measurements of the scattering parameters [S] and radiation patterns. The minimum gain of a single antenna with all the other three elements terminated in 50O loads is 1.49dBi, while the isolation is over 25dB between all the MIMO antennas located in the array structure. The measured results suggest that the antenna is well suited for LTE MIMO applications as well as handset antennas.
We recently introduced large, lightweight, broadband plano-convex RF lens for close-range measurement of far-field antenna radiation pattern [1]. While the lens can drastically reduce the phase variation of the field across the transverse plane at a relatively short distance from the lens, the amplitude of the field in the same plane is affected by the diffraction from the circular edges of the lens, and to some extent by the transmitted field after internal reflections inside the lens. Furthermore, while the phase variation is minimal (within ±10°) and almost independent of the distance of the transverse plane from the lens, the field amplitude variation across the same plane increases with the distance of the plane from the lens. The amplitude variation reduces the useful size of the "quiet zone". To reduce the amplitude variation, we propose to incorporate "matching layers" around the lens. As we shall demonstrate in the paper, these matching layers help to reduce the aforementioned diffraction and internal reflections. As a result, the amplitude variation of the field across the transverse plane is reduced (to within ±1dB), thereby increasing the size of the "quiet zone". The matching layers are effective even for lenses as small as 6 in diameter.
This paper presents V-band radiation pattern characterization of both low- and high-directivity antennas. A fourarm micro-machined spiral antenna with monolithically integrated mode-forming network designed for dual circularlypolarized radiation represents the low-directivity antenna, while a standard gain horn is used for the highly directive antenna. All measurements were performed using an in-house NSI-700S- 30 system capable of spherical near-field measurements from 1-50 GHz and direct far-field measurements from 50-110 GHz. Complete comparisons of simulated, near- and far-field patterns show the feasibility of near-field measurements in V-band. Based on pattern comparison and measurement statistics conclusions are drawn about V-band near-field measurements.
Reconfigurable radar antennas with rapid, real-time control of the radiation pattern beamwidth provide expanded performance for many instrumentation radar applications, including RCS signature measurement and dynamic Time Space Position Information (TSPI) radar tracking applications. Adaptive adjustment of antenna radiation patterns was traditionally accomplished by electro-mechanically selecting predefined aperture dimensions that corresponded to desired beamwidths (e.g., ? ?/D). For an array antenna consisting of as few as 200 elements, beam shaping can be accomplished by adjusting the relative phase of individual array elements, a technique defined as beam spoiling or decollimation. This paper analyzes an operational radar antenna array incorporating reconfigurable beamwidth and beam shape through independent phase control of each subaperture. By adjusting the relative phase of radiating elements, the system can illuminate a programmable field of regard with full transmit power. For this array, the phase distributions across the elements map to a smaller "virtual aperture" displaced behind the physical array. Theoretical and measured results are presented to validate the reconfigurable array pattern control technique.
ABSTRACT When the mechanical requirements are established for a spherical near-field scanner, it is desirable to estimate what effects the expected mechanical errors will have on the determination of the far field of potential antennas that will be measured on the proposed range. The National Institute of Standards and Technology (NIST) has investigated the effects of mechanical errors for a proposed outdoor spherical near-field range to be located at Ft. Huachuca, AZ. This investigation was performed by use of theoretical far-field patterns and introducing position errors into simulated spherical near-field measurements using software developed at NIST. Periodic and random radial and angular position errors were investigated. Far-field patterns were then calculated with and without probe-position correction to determine the effects of mechanical position errors. Periodic errors were found to have a larger effect than random errors. This paper reports the results of these investigations.
Although the square patch antenna is a well known printed circuit antenna, there are gaps in the publications that prevented accurate design for practical dual polarization patch antennas. This paper describes (without gaps) the steps that allow rapid design of the dual polarized square patch antenna with typical commercial RF materials. Given a patch laminate material, the design process proceeds by using the Matlab program which is given in Appendix A. Typical values for a 5 GHz patch antenna are given. Dual polarization square patch antennas were constructed. Measurements show the two ports are well isolated, and they provide polarization diversity which is useful in our MIMO array development program. The scattering matrix of the two port antenna was measured with an Agilent PNA network analyzer. The antenna patterns were measured in our anechoic chamber and on our far field range. The pattern widths provide hemispherical coverage. The results which are given imply good efficiency for the antenna ports. When combined with the other patch elements in the MIMO array, robust communications are achieved for all look angles.
The Antenna Metrology Lab at the National Institute of Standards and Technology in Boulder Colorado has developed a robotically controlled near-field pattern range for measuring antennas and quasi-optical components from 50 GHz to 500 GHz. This range is intended to address the need for highly accurate antenna pattern measurements above 100 GHz for a variety of applications including remote sensing, communications and imaging. A new concept in near-field range systems, this system incorporates the positioning repeatability of a precision industrial six-axes robot, six-axes parallel kinematic hexapod, and high precision rotation stage, integrated with a highly accurate laser tracking system. Programmable robot positioning allows the system geometry to be configured for spherical, planar, and cylindrical scans, as well as gain extrapolation measurements. Variable scan volume accommodates different test antenna sizes. Positioning accuracy better than 10 µm is predicted. Specifics of the system design, operating specifications and configurability will be presented.
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 in 2007 at CEA for indoor near field monostatic RCS assessment. This experimental layout was composed of a 4 meters radius motorized rotating arch (horizontal axis) holding the measurement antennas while the target was located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allowed full 3D near field monostatic RCS characterization. A new study was conducted in 2011 in order to achieve a more accurate positioning of the measurement antenna. The main objective is to enhance the RCS measurement performances, especially the environment subtraction directly related to the positioning repeatability of the measurement antenna. This new mechanical design has therefore been optimized to allow a +/-100° azimuth range with an angular positioning repeatability of less than 1/1000°. To achieve this level of accuracy, several keys design elements were considered: robust mechanical design, position control system… This paper describes the new experimental layout and the results of a positioning accuracy assessment campaign conducted using a laser tracker.
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 in 2007 at CEA for indoor near field monostatic RCS assessment. This experimental layout was composed of a 4 meters radius motorized rotating arch (horizontal axis) holding the measurement antennas while the target was located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allowed full 3D near field monostatic RCS characterization. A new study was conducted in 2011 in order to achieve a more accurate positioning of the measurement antenna. The main objective is to enhance the RCS measurement performances, especially the environment subtraction directly related to the positioning repeatability of the measurement antenna. This new mechanical design has therefore been optimized to allow a +/-100° azimuth range with an angular positioning repeatability of less than 1/1000°. To achieve this level of accuracy, several keys design elements were considered: robust mechanical design, position control system… This paper describes the new experimental layout and the results of a positioning accuracy assessment campaign conducted using a laser tracker.