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CEA has developed a hyper frequency generator consisting of a high voltage one pulse power supply coupled with a Vircator capable of radiating a 1 GW electromagnetic field at 2 GHz, for 100 ns. The device is enclosed in a large building. It was first necessary to verify that the levels generated were below European safety levels on human exposure to radio-frequency electromagnetic fields. Measurements and calculations were performed for that purpose. Given the large dimensions of the building in comparison with the electromagnetic wave, the experimental hall was modeled by optical methods. A ray tracing program was written taking account of the field attenuation with distance and multiple wall paths with scattering reflections. The results were compared to those of an exact program dedicated to optics with diffuse back scatterings. Measurements were previously performed with a hyper frequency low power generator in the place of the Vircator. A mode converter enables the same electromagnetic field to be radiated (TM mode). This methodology enables the detection of any electromagnetic leakage in the building and its correction, and, finally, the validation of the facility, optimizing the number of measurements.
We summarize here a number of advances in Impulse Radiating Antennas. These devices are composed of a reflector and a broadband feed. We have demonstrated improved gain and reduced crosspol by using feed arms located at ±30° to the vertical, as opposed to the original design that placed the arms at ±45°. We have reduced the return loss (flattened the TDR) at the splitter, at the feed point (focus), and at the resistors in the feed arms. We have added a ground plane that enhances mechanical stability and reduces crosspol. We have also improved the mechanical stability of the feed point.
This paper describes an evaluation of RCS measurements using a free-space focused beam system. Issues including effects from the Gaussian beam width and uncertainties associated with the system have been considered. Measurements and predictions of a generic embedded structure show close correlation over the frequency range of interest and indicates that this technique is ideal for rapid, accurate RCS measurements of physically small features.
A method for detecting a single faulty element in a linear array using neural networks is presented. A feed forward back propagation neural network is trained to detect the faulty element. Given the error patterns due to the faulty array, the network can predict the number of faulty element. A linear array of 21 elements with uniform excitation and uniform spacing is considered. Indexing Terms: Array, Neural Networks, Feed Forward, Back Propagation.
Using the results of the analysis, a script program was developed for the NSI2000 software that would calculate the spectrum from the input parameters, perform the filtering and calculate the hologram using the Fast Fourier Transform. The change in the amplitude of the reconstructed hologram pulse is then used to determine the error that results in the calculated element amplitude and/or phase. Sample curves are generated to illustrate the technique.
Abstract This paper describes the modernization of Planar Near-field Antenna Measurement Systems at NGST (Northrop Grumman Space Technology). The original systems, over 15 years old, utilized granite-based CMMs (Coordinate Measurement Machine) that were adapted and controlled by custom software and computers. The new systems with new custom software, computers and RF hardware are described. Productivity has been dramatically improved – in some cases by a factor of 10.
Doing EIRP measurements in a nearfield facility is a known procedure. However, if the transmitted power is relative high, options are limited and care must be taken to prevent damage on equipment and absorbers. This paper describes how EIRP and pattern measurements for high power antennas and transmitters can be done in an indoor facility, and describes various considerations, choices and practical aspects. An example shows that even high power wide-band systems can be measured in near-field facilities.
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.
A piecewise linear model of the Kramers-Krönig (K-K) relations has been used to analyze electromagnetic dispersion data on RF polymers and composites. This KK analysis revealed that concrete knowledge about the complex low frequency material dispersion is critical to the analysis and understanding of the microwave dispersion. Furthermore, the confidence in the material dispersion measurements may, to someascertained through use of the K-K relations. degree, be
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.
At the Fraunhofer IIS many antenna design and measurement problems deal with electrically small antennas for different wireless communication links. Therefore we want to establish a meaningful procedure to measure the pattern and also the gain of these antennas quite exactly.
ABSTRACT This paper describes a broadband radome measurement method that provides insertion loss performance referenced to circularly polarized radiation. The measurements are performed using linearly polarized sources and post processing is employed to convert to circular polarization. The method reduces measurement errors encountered using circularly polarized sources that traditionally have poor cross polarization isolation.
Abstract Standardization, accuracy and uncertainty are important considerations to the electromagnetic material measurement community. Test requirements, available hardware and material sample limitations can all add variance to each of these factors. This paper presents comparative data from the Boeing-Tulsa and Boeing-Philadelphia RF reflectivity arches for the purpose of illustrating a process of system performance verification. This initial study is intended to foster discussion within the community and to better understand discrepancies among the various test systems.
The reflection coefficient of an antenna impacts the power transmitted by the antenna. Accurate characterization of this parameter is important in a communication or radar system. This paper discusses an implementation whereby a reflectometer is located near the antenna under test in an antenna range albeit far from the receiver. By placing the reflectometer near the antenna, the measurement uncertainty intrinsic to long cable runs can be minimized.
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.
In a previous work by the authors, the Groundwave Correction Method for measuring the gain of an unknown antenna over a seawater groundplane in the 2-100 MHz band was introduced [1]. The limitations of this method as the frequency delves further into the VHF band will be explored in this paper. Additionally, the effects of the environment surrounding the transmit site will be discussed with a goal of providing a more accurate GCM formulation.
A new antenna and RCS measurements facility consisting of four anechoic chambers has recently been constructed at MIT Lincoln Laboratory. The facility was designed with a rapid prototyping focus. The four chambers include a tapered chamber covering the 225 MHz to 18 GHz band, a millimeter wave rectangular chamber covering 4 to 100 GHz, a large rectangular anechoic chamber covering 150 MHz to 20 GHz, and a large compact range covering 400 MHz to 100 GHz. The compact range will be highlighted.
This paper describes a Composite Near-Field Scanning Antenna Range for frequency bands that extend from X- Band in the microwave frequency regime through W- Band in the millimeter-wave regime – i.e. 8.2 through 110 GHz. We show some of the initial checkout data using pyramidal standard gain horns and compare the patterns to theory.
We estimate uncertainties in the test antenna transmitting function due to uncertainties in the near- field measurements and in the probe receiving function.