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A material measurement technique is developed to simultaneously characterize electric and magnetic properties for homogeneous lossy material in a parallel-plate region. The material is excited by a rectangular waveguide which interacts with the parallel-plate region through a slot. In order to extract the complex constitutive parameters from the material two independent measurements are required. If the material is attached to a PEC surface and is unable to be removed, the most obvious manner to characterize the material is a parallel-plate region. This paper demonstrates through the use of a magnetic field integral equation (MFIE) how a rectangular waveguide interacting through a slot with a parallel-plate region can be used to obtain two independent measurements, which are necessary for characterizing the homogeneous lossy material. At last year proceedings, the formulation of this technique was presented assuming an infinitely thin wall-thickness. The formulation has now been altered to include the effects of finite wall-thickness, for which theoretical and experimental results are shown to validate the formulation. Thus, the focus of this paper is on the crucial influence of finite wall thickness, future results will focus on the material extraction process.
Calibration of planar near field probes is generally required to obtain accurate cross-polarization measurements of satellite antennas; however, probe calibration is costly and time consuming. One way to avoid probe calibration is to ignore the probe cross-polarization and use the probe co-polarized patterns alone for probe correction. Then the probe can be easily characterized by standard, in-house measurements or by analytical models. Of course, if the probe cross-polarization is ignored, additional errors are introduced in the co- and cross-polarized pattern measurements, but the errors can be manageable, depending on the probe and Antenna-Under-Test (AUT) polarization properties. Complete formulas and/or tables for near field measurement errors for three popular measurement configurations are presented, along with experimental verification of the error estimates for one case.
This paper presents the method of determination of the amplitude and phase distribution in antenna plane aperture. This method is based on homodyne one, where the initial microwave oscillation is heterodyne one. The mobile probe unit consists of proper antenna probe, controlled phase shifter, high-frequency receiver. The initial microwave oscillation is shifted on low frequency with controlled phase shifter. The phase shifter is fed with low frequency modulating signal with modulation of carrier in high frequency band. The initial phase of low-frequency oscillations is transferred on microwave. The initial phase and frequency of microwave oscillations are eliminated in mixer. Low-frequency measurements of amplitude and phase difference are carried out.
Serrations are often applied at the edges of compact-range reflectors in order to reduce the scattering from the edges into the quiet zone. At low frequencies the serrations show different scattering of the field at the two polarisations: parallel to and perpendicular to the serration teeth. This has been verified by modelling a range by the Method of Moments (MoM). The size of the range reflectors is about 7.5 m by 10 m which make the re-flectors difficult to handle by MoM even at a fre-quency which is low for the range, viz. 1.7 GHz, in which case the reflectors are each 2400 wavelengths squared. A narrow strip, horizontal or vertical, across the re-flector and closed by a single serration tooth at each end is shown to give a good prediction of the field along a line parallel to the strip in the quiet zone. By this simple model of the range it has been demon-strated that the quiet-zone field depends highly on the polarisation. When the polarisation is parallel to the teeth the quiet-zone field has ripples which are 0.3 dB peak-to-peak, but for the perpendicular polarisation the field variations are 0.8 dB peak-to-peak. The results are compared to quiet-zone fields deter-mined by Physical Optics (PO).
This paper describes the Rectangular Coaxial 40’ long measurement system recently designed and installed at AEMI with the primary purpose of measuring the reflectivity of its high performance VHF/UHF absorbing materials in the frequency range 30 – 510 MHz. The basic principles of the system are described in detail in [1] and are based on S11 – measurements of absorbing material reflectivity by a Vector Network Analyzer (VNA). In order to improve the system productivity and measurement accuracy it was enhanced by the time-gating software option – the standard option of ORBIT/FR Spectrum 959 automated measurement software package [2].The measurement system performance was thoroughly evaluated and validated by a number of tests performed in the “empty” coaxial line, and in the line loaded by absorbing materials. The list of RF uncertainties – various measurement error sources - was generated, the main measurement error contributors were identified, the corresponding errors – estimated and the overall RSS measurement errors were calculated for the absorber reflectivity varying in the range of -30dB to – 40dB.
Commercial windmill driven power turbines (“Wind Turbines”) are expanding in popularity and use in the commercial power industry since they can generate significant electricity without using fuel or emitting carbon dioxide “greenhouse gas”. In-country and near-off shore wind turbines are becoming more common on the European continent, and the United States has recently set long term goals to generate 10% of national electric power using renewable sources. In order to make such turbines efficient, current 1.5 MW wind turbine towers and rotors are very large, with blades exceeding 67 meters in diameter, and tower heights exceeding 55 meters. Newer 4.5 MW designs are expected to be even larger. The problem with such large, moving metallic devices is the potential interference such structures present to an array of civilian air traffic control radars. A recent study by the Undersecretary of Defense for Space and Sensor Technology acknowledged the potential performance impact wind turbines introduce when sited within line of site of air traffic control or air route radars. [1]. In the Spring of 2006, the Air Force Research Laboratory embarked on a rigorous measurement and prediction program to provide credible data to national decision makers on the magnitude of the signatures, so the interference issues could be credibly studied. This paper, the first of two parts, will discuss the calibrated RCS measurement of the turbines and compare this data (with uncertainty) to modeled data.
A device and algorithm of measuring of microwave airborne radar antenna impedance and input power level are presented. A compact five-port microwave reflectometer, p-i-n diodes switch, single microwave detector are used. The output detector signal is processed. All of that results in decreasing of the cost of equipment, elimination of instrument components non-ideality and reaching of high equipment accuracy.
The DGA/CELAR (France) (Centre d'Electronique de l'Armement: French Center for Armament Electronics) is able to measure targets in order to get their RCS (Radar Cross Section). Yet CELAR RCS measurement facilities are not compact bases and therefore the measured field is a near field. This article proposes a solution allowing the transformation of this near field to a far field and this in the three dimensions of space without limiting any dimension with Fraunhöfer criterion. Thanks to this method the RCS of a target is able to be known in any direction of space and moreover the calculation of a three-dimensional ISAR (Inverse Synthetic Aperture Radar) picture is thus possible. At first the theoretic part of our work is presented. Then a fast method in order to calculate the transformation of a near field to a far field by optimising the calculation time thanks to signal processing theory is given. Finally obtained results from simulated bright points are presented.
ABSTRACT A new probe compensated near-field – far-field transformation technique with planar spiral scanning is here proposed. It is tailored for quasi planar antennas, since an oblate ellipsoid instead of a sphere is considered as surface enclosing the antenna under test. Such an ellipsoidal modelling is quite general (containing the spherical one as particular case) and allows one to consider measurement planes at a distance smaller than one half the maximum source size, thus reducing the error related to the truncation of the scanning surface. Moreover, it reduces significantly the number of the needed near-field data when dealing with quasi planar antennas. Numerical tests are reported for demonstrating the accuracy of the far-field reconstruction process and its stability with respect to random errors affecting the data.
A novel approach using Artificial Neural network (ANN) is proposed to identify the number of faulty elements present in a uniform linear array consisting faults in multiple elements. The input to the neural network is amplitude of deviation pattern and output is the number of faulty elements. In this work, ANN is implemented with three different algorithms; Radial Basis Function neural network (RBF), Generalised Regression neural network (GRNN) and Probabilistic neural network and their performance is compared. The network is trained with some of the possible faulty deviation patterns and tested with various measurement errors. It is demonstrated that the method gives a success rate of 93.4%.
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. The experimental layout is composed of a motorized rotating arch (horizontal axis) holding the measurement antennas. The target is located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allows full 3D near field monostatic RCS characterization. Two bipolarization monostatic RF transmitting and receiving antennas are driven by a fast network analyser : - an optimised phased array antenna for frequencies from 800 MHz to 1.8 GHz - a wide band standard gain horn from 2 GHz to 12 GHz. This paper describes the experimental layout and the numerical post processing computation of the raw RCS data. Calibrated RCS results of a canonical target are also presented and the comparison with compact range RCS measurements is detailed.
The DGA/CELAR (France) (Centre d'Electronique de l'Armement: French Center for Armament Electronics) is able to measure targets in order to get their RCS (Radar Cross Section). Once this RCS is acquired it may be very interesting to calculate RADAR pictures of these targets because RADAR picture allows emphasizing the bright points. Until now, CELAR produced images in two dimensions, but these pictures have shown their limits in order to locate problems in altitude. This article fills this gap while proposing two methods in order to get an image in three dimensions: a method using a three-dimensional Fourier transform and a method based on interferometry.
This paper describes the details of a specialized data acquisition system developed at the David Florida Laboratory. The system acquires, monitors, records and performs post measurement analysis of passive intermodulation (PIM) and multipaction events observed during RF testing. This characterization of components and systems carrying radio frequency signals is an important element of space qualification of satellites and other space faring systems. A National Instruments PXI chassis equipped with a PXI-4462 acquisition card and a LabView based software application was implemented to digitize the resulting data. A second application provided by InfoBright permits the compact storage of hours of measured data in its entirety (multiple channels each sampled at over 200,000 samples per second) using a specialized real time data compression scheme. The application also permits quick retrieval of relevant data segments using SQL query processing. Performance of this solution is presented along with its effectiveness in detecting details of PIM and multipaction events.
A new method is here proposed to accurately evaluate the Specific Absorption Rate (SAR), e.g. of a mobile phone, through free-space measurements. The method takes advantage of the simple yet powerful plane-wave spectrum (PWS) representation of the electromagnetic (EM) field. The emitting device is tested in an anechoic chamber, where the two tangential components of the electric field are measured (amplitude and phase) and expanded into their PWS. These experimental data are subsequently fed to an equivalent transmission-line representation of the planar stratified structure composed by stacking the half-space made of free-space and the stratified flat phantom. Numerical simulations have shown that this method allows to accurately reconstruct the E field distribution inside a homogeneous phantom, with a worst-case error of 26 % in the estimation of the peak E field [1,2]. Furthermore, the proposed method is the first practical procedure for assessing the SAR in a stratified phantom, where the standard approach of moving a probe inside a liquid-filled phantom is no more feasible.
If an acquired RF field data set captures all the radiated energy, transformations will have minimal errors. However, it is sometimes impractical to capture the complete radiated field. In this case, some sort of edge treatment is required before transforming the data set. Usually, a function such as a cosine taper is added to the edge to minimize transformation errors. Unfortunately, these functions may be discontinuous to the measured data and its’ derivatives. This paper will present a method of truncation which matches the measured data and its’ derivatives. It will then transform the RF field data to the compact range reflector surface and compare the results of several truncation methods.
The present paper introduces a lower frequency design for the open boundary quadridge horn (OBQH) introduced in [1]. This new horn cover the UHF band and it is usable up to 6GHz. It exhibits a fairly uniform radiation pattern at the upper end of its range as well as a fairly flat gain as was the case with the higher frequency design. The increased frequency band up to 6GHz is accomplished by the use of a ferrite filled cavity that maintains a good VSWR even when the feed cavity is reduced to avoid higher order modes that cause the main beam of the pattern to split. As with the higher frequency design this horn can be used as a source in antenna pattern measurement chambers and even reflectors. As a second part to the paper some data is presented on the use of the S to Ku Band OBQH as a feed for reflectors used in Radio-Astronomy [2]. The results show that by placing the OBQH in an absorber lined cavity the pattern improves and the feed becomes more effective.
In order to ensure proper measurements in the compact range, the reflector needs to be aligned within the range. Unfortunately, the reflector does not have any direct method of leveling or locating such as straight edges or fiducials at known locations. The only known reference is the ideal point cloud. As the point cloud is given, it is oriented correctly in the range. So by centering the point cloud in the range, the compact range reflector can be aligned to the range by minimizing its deviation from the ideal point cloud. This paper will go through the mathematics used to accomplish this alignment in the translation along and rotation about the three primary axes. In addition, it will give a method of determining reflector twist. The method is sufficiently generic that it can be applied to other shapes and figures of merit.
The 2004 AMTA paper entitled “The “Cam” RCS Dual-Cal Standard” introduced the theoretical concept of the “cam,” a new calibration standard geometry for use in a static RCS measurement system that could simultaneously offer multiple “exact” RCS values based on simple azimuth rotation of the object. Since that publication, we have constructed a “cam” to further explore its utility. The device was fabricated to strict tolerances and its as-built physical geometry meticulously measured. Utilizing these characteristics and moment-method analysis, a high-accuracy computational electromagnetic (CEM) “exact” file required for calibration was produced. Finally, the “cam” was evaluated for its efficacy as a single device that could be utilized as a dual-cal standard. This development was conducted with a particular focus on the hypothesized improvements offered by the new standard, such as the elimination of frequency nulls exhibited by other resonant-sized calibration devices, and improved operational efficiency. In this follow-on paper, we present the advantages to and challenges involved in making the “cam” a viable RCS dual-cal standard by describing the fabrication, modeling and performance characterization.
In the Flight Model (FM) of the PLANCK telescope, the feed horns are connected to either HEMTs or bolometers operating at cryogenic temperatures to detect the Cosmic Microwave Background radiometric signal. For the purpose of an overall alignment verification at ambient temperature, reflectivity measurements will be performed using an auxiliary feed horn that is terminated with a switching diode. This verification test will be conducted at 320 GHz, to benefit from the narrow beam and a high sensitivity to misalignment. To perform the reflectivity measurements, an additional “circulator” with low loss and high isolation between transmit and return channels had to be developed. Besides that, the circulator co-locates the phase centres of both Tx and Rx range antennas on the focal point of the CATR, which allows monostatic reflectivity measurements. Quasi-optical techniques have been used to design a circulator that meets these requirements. The assembly has been developed, tested and used for reflectivity measurements.
ACC has developed for the ESA-ESTEC CATR a compact but highly versatile 5-axis positioner. It is composed of a roll axis, upper azimuth, elevation, translation and lower azimuth axis. The clearance between the floor and the translation stage is designed to pass over a 12” walkway absorber while the roll axis height is only 155 cm (~5 feet). The standard configuration for medium or high gain antennas is the roll-over-azimuth or elevation-overazimuth configuration with a vertical interface for the AUT. For omni-directional antennas and RCS measurements, the positioner can be configured as a low profile azimuth positioner with a horizontal interface without a blocking structure behind the AUT. The positioner can also be configured for bistatic RCS measurements and Spherical Near Field. With the addition of a linear scanner, the Quiet Zone can be scanned in a polar way but also planar scanning is possible. Other key parameters are: angular accuracy: 0.01°, accuracy of the translation axis: 0.01 mm, load capacity 100 kg.