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Standard Gain Horns (SGH) are utilized frequently either as measurements antenna or as reference antenna in antenna gain measurements by comparison or substitution method [1]. They also find use as source antennas in anechoic test chambers and for many other purposes such as fixed site antennas. The most widespread SGH geometry has a rectangular cross-section and is pyramidal with optimized geometry to achieve maximum gain [2, 3, 4]. When used as a precision gain reference in antenna measurements the SGH is often calibrated by a reference facility or another third party. When external or internal calibration means are not available the SGH peak gain is often determined directly from the reference tables of the NRL report [2]. The quality of the original work is such that even today the associated uncertainty on these peak gain values are generally accepted to be within +/-0.3dB [1]. In this paper the accuracy of the NRL gain tables are investigated by comparison with a full wave numerical method based on FDTD [7] and measurements in different antenna test ranges. Performance variation of the SATIMO Standard Gain Horns due to the manufacturing and measurement accuracy has been also investigated with conducted and radiated experiments.
A ground station antenna for Galileosat application operating in right hand circular polarization at P-band has been designed, manufactured, and tested. Other than stringent environmental requirements for typical ground station antennas the specification call for an antenna with very stringent requirements on pattern shape and symmetry and a very severe control on side and back lobes. In order to ease the requirement on the antenna positioner the antenna should have very compact size and low weight. The final antenna consists of an array of 7 medium gain, dual linear polarized yagi elements as shown in Figure 1. This paper describes the antenna design trade-off activity including the selection of the most suited antenna technology and manufacturing details. It also reports on the testing in the SATIMO SG-64 multiprobe spherical near field test range with considerations on the associated measurement uncertainty. The final acceptance of the antenna was based on measurements performed in CNES and SATIMO.
The Mini-RF instrument on NASA’s Lunar Reconnaissance Orbiter is gathering data toward its science goal of probing the permanently shadowed terrain for the presence of water near the lunar poles. The circular polarization ratio is the central parameter used to characterize the lunar surface using Mini-RF radar returns. Accurate use of this parameter requires on-orbit polarimetric characterization of the instrument. This is done with a combination of measurements. Indirect measurements are performed by pointing the radar at the lunar surface to remove any asymmetry in the surface backscatter. Direct characterization of transmit and receive portions of the Mini-RF radar are performed using Earth-based resources. The Earth-based resources include the: Arecibo Radio Telescope, Green Bank Telescope, and Morehead State University Space Tracking Antenna. This paper describes the measurement approach and a sample of results. The primary measurements of interest include: principal plane antenna patterns, transmit polarization ellipse, receiver amplitude and phase balance, and antenna bore sight direction. These measurement values are incorporated into the Mini-RF SAR data processing to produce quality, calibrated CPR measurements
This paper shall discuss a method for measuring the current distribution – in both magnitude and phase - along the length of a floating antenna operating on the surface of the ocean. The method makes use of a novel toroidal current sensing device and balun arrangement, with a vector network analyzer serving as the measurement instrument. The current data obtained using this method can then be used to compute the far-field pattern of the antenna, both at the horizon and overhead, in a manner similar to near-field scanning of aperture antennas. This new method has significant advantages over the conventional far-field method of measurement in terms of accuracy, time, and cost, and can also be used to determine the realized gain of the antenna. Measured and theoretical data shall be presented on example antennas to illustrate the process of measuring the current distribution as well as computation of the far-field pattern.
An optical diffraction technique was developed for performing far field transformations of spherical near field data. The first goal of the development was to promote a better physical understanding of the phenomena of spherical near field transformation. Along the way, the limitations of this type of measurement became associated with real, optical physics, thus providing new considerations that might not be easily derived from the traditional, multi-pole expansion of spherical waves. In addition, new applications of spherical near field measurements are suggested by this approach. Specifically, the optical method allows for better understanding of the necessity and application of probe compensation. An optical transform eliminates the need for axially symmetric probes. Perhaps more importantly, this understanding leads to new considerations toward the applicability of single scan, spherical transforms which may lead to significant increases to the effective lengths of far field ranges. The purpose of this paper is to present a conceptual foundation to the spherical transformation of near field data by optical means and the immediate, associated benefits.
The equivalent source approach [ 1-4] has been presented recently as an advanced antenna diagnostics tool. The equivalent source approach is a true 3D approach as opposed to traditional methods based on plane wave expansion using hemispherical field information. This method is therefore highly suitable for diagnostics on low and medium directivity antenna and even allows the possibility to isolate, identify and filter unwanted effects close to the antenna from the measurements such as cable interactions. Spatial filtering is used in spherical near field measurements through the truncation of the mode spectrum. From knowledge of the minimum sphere enclosing the Antenna Under Test (AUT) the minimum number of spherical modes needed to represent the antenna can be determined and information resident in the higher order modes are eliminated as associated to sources outside the spatial domain of the source. Due to the nature of the spherical waves, spatial filtering truncation cannot be performed too close to the physical minimum sphere enclosing the antenna. Since the equivalent current approach is based on an accurate reconstruction of the physical currents on an object slightly larger than the physical antenna, a more acute spatial filtering can be performed. This paper discusses the advantages that can be obtained from the 3D spatial filtering on spherical near field antenna measurements.
The spherical near-field antenna measurement system StarLab has recently evolved to cover the entire frequency band from 800MHz to 18GHz [1, 2, 3]. The system is based on patented probe array technology and the Advanced Modulated Scattering Technique (A-MST) [4, 5]. The StarLab system combines the speed advantages of a probe array with mechanical rotation in elevation, thereby allowing for unlimited angular resolution over the full 3D sphere. By adding a linear scanner, the StarLab system can be converted to a compact cylindrical near-field measurement system (Starlab BTS), as shown in Figure 1. This system is particularly well-suited for measurements of base stations and other sectorial type array antennas. This paper describes the innovative design aspects of the StarLab portable antenna measurement system, with emphasis on the cylindrical near-field measurement capabilities. The system validation testing has been performed with comparative measurement campaigns, including both multiprobe and other traditional (single probe) measurement facilities at customer locations.
RF measurement of the dielectric properties of very thin films (less than 1/100 wavelength thick) presents a challenge using traditional techniques. Many techniques, such as conventional transmission line-type measurements, are not sensitive enough to measure a single thin sheet of material. Moreover, in the case of waveguide, the method of mechanically fastening the material in place properly is challenging. In this paper, we explore several different strategies for measuring thin films and compare the merits of each. In particular, coaxial line measurements with stacked layers, waveguide measurements, and cavity measurements are discussed. The methods will be compared in terms of their accuracy and sensitivity. Measurements are carried out using the various methods on several low-loss thin-film materials. The measurements are then compared and validated using known reference materials.
This paper elaborates on certain aspects of a new measurement process that permits an assessment of spherical near-field (SNF) measurement errors based on a set of practical tests that can be done as part of any SNF measurement. It provides error bars for a measured radiation pattern in an automated fashion.
Anechoic chambers utilized for far-field antenna measurements at VHF/UHF frequencies typically comprise rectangular and tapered designs. The primary purpose of conventional far-field chambers is to illuminate a test zone surrounding the Antenna Under Test (AUT) with an electric field that is as uniform as possible, while multiple reflections from the side wall absorber assemblies are kept to a minimum. The cross section dimensions of far field chambers at VHF/UHF frequencies can be electrically small, often as little as 3.. In this paper the side wall reflections at VHF/UHF bands are studied in more details for elongated rectangular and tapered chambers. In particular, the reflectivity is evaluated in rectangular chambers as a function of electrical dimensions of the chamber cross – section and of the ratio W (width of the chamber) or H (height of the chamber) to L (length – separation between antennas) for values ranging from 0.5 to 2. The methods of reflectivity improvement are presented and compared. In particular, the conventional chamber design is compared with a “Two Level GTD” approach [4,5,7] and the latter one shows significant reflectivity improvement in the test zone, even at longer source antenna AUT separations. The side wall reflections are examined in tapered chambers as well. The back wall reflection mechanism, which assumes multiple incident waves – direct from the source antenna and reflected from the side walls, floor and ceiling, is offered and confirmed by the simulation, which, in turn, yields an optimized back wall chamber design (see also [6]).
The in-flight pattern measurements of a sub-millimetre space telescope may be improved by de-termining the actual reflector anomalies and then in-clude the knowledge to these in the final pattern de-termination. The pattern measurements with a celes-tial object as source often have an insufficient signal-to-noise ratio for a pattern prediction outside the main lobe. Repeated measurements may improve this but even better is the possibility to extract data from different detectors operating at different frequencies. With the Planck Space Telescope as example, simulations of a displaced and distorted reflector have been carried out for noise contaminated amplitude measurements of Jupiter by 5, respectively 10, differ-ent detectors. First, the main beams of the antenna patterns are retrieved in a regular grid. Here the ac-curacy is limited by the noise level. Then, by a Physi-cal Optics optimization the actual distortions of the telescope's reflector are determined so that the calcu-lated radiation patterns of the antenna are correlated to the measured main beams. The patterns for the optimized and retrieved reflector geometry are shown to be precise at levels far below the noise floor in the direct measurements1. 1 The work presented in the paper has been carried out under ESTEC Contract No. 18395/NL/NB
This paper describes the principles of operation of high performance absorbing materials and the criterion for its performance optimization at UHF/VHF frequency bands. The optimization criterion is intended to determine the optimum carbon loading of the foam based absorber components, thus delivering optimal reflectivity of the full absorbing assembly (foam based absorber components on a metallic backing plate) at the lowest possible operating frequency. The optimization is based on equalization of reflections in the time-domain from the front face surface of the absorbing component and from the backing metallic plate. Validity is confirmed by measurements of the reflectivity of pyramidal absorbing components of varying heights, (3’, 5’, 6’ and 8’) in a 40’ long coaxial line terminated in a metallic back wall. In addition, it is shown that the “aging” process of the absorbing components can be characterized by the change of the effective reflectivity in the time-domain of the components as a function of aging time. It is possible to determine whether the absorber performance is stabilized and the “aging“ process is complete, and whether the loading of the absorber carbon mix is optimum, or is otherwise under-loaded or over-loaded. In particular, it is possible to determine prior to the time when the “aging” process is stabilized whether the loading is excessive.
In this paper, a symmetrically feeding structure for linear dual-polarized feeds is put forward. Due to its electrical balance and modes within the circular feeding waveguide are compressed. The polarization purity of feeds is then improved. Thus the level of cross-polarization can be very low, which is the key performance requirement for CATR (Compensated Compact Test Range). Besides, the return loss equation derived from equivalent microwave network for this symmetric structure is different from the ordinary single port feeding structure. In the low frequency range application, reflection at interface between coaxial and circular waveguide can reach a high level, a new transition probe is designed to depress it. Simulation results show that VSWR and cross-polarization performances of symmetric feeding feeds both are better than dual-polarized quadruple-ridged horn. 01TM21TE
From measurements of RCS of a target as a function of the frequencies and the bearings, it is possible to make RADAR imagery. A common way is to use a bi-dimensional Fast Fourier Transform (FFT2) while this algorithm being very fast. Yet this algorithm demands that the grid on which the RCS is known fulfils some particular conditions. Now such conditions are not respected by the grid of measurement. Consequently an interpolation of this grid is necessary in order to be able to apply the FFT2 algorithm. The choice of the method of interpolation will directly impact the quality of the calculated RADAR image. In this article we propose to study this impact while giving the analytical expression of the interpolation then while giving the analytical expression of the RADAR image calculated from the interpolated RCS and while specifying eventually the method interpolation which limits the degradation of quality of the calculated RADAR image.
This paper discusses the designing of circular waveguide antenna, mode & field propagation analysis with in circular waveguides, cutoff frequency analysis & radius along with calculations for millimeter region Electromagnetic waves ranging between 1GHz-40GHz.This analysis will be based on Finite Element Method using Ansoft HFSS, therefore Finite element Method has also been briefly discussed. Circular waveguide’s cutoff frequency & radius can be directly calculated by using SAND’s constant; a method generated through the optimization of approximated cutoff frequency equation refined by using FEM numerical technique. Graphical analysis for cutoff frequencies ranging between 1GHz-40GHz against waveguide radii has also been discussed. SAND’s constant variation for entire frequency range of 1GHz-40GHz have also been discussed.
A stand-alone commercial program, performing advanced electromagnetic processing of measured data, is being developed by TICRA. The program reads the measured field and computes the extreme near field or the currents on the antenna surface. From the inspection of the extreme near field or currents, the program will solve typical antenna diagnostics problems, such as identification of array element failure and antenna surface errors, but also allow artificial removal of undesired contributions, such as currents on cables and fixtures, thereby saving valuable time and resources in the antenna design and validation process. The program will be based on two field reconstruction techniques, the SWE-PWE presented at AMTA in 2007, and a new and more accurate inverse higher-order Method of Moments (INV-MoM). The paper will illustrate the theory behind the two techniques and present numerical cases with simulated data.
– far-field transformation with cylindrical scanning are efficiently determined by using an optimal sampling interpolation algorithm. The comparison of the far-field patterns reconstructed from the acquired irregularly distributed measurements with those obtained from the data directly measured on the classical cylindrical grid assesses the effectiveness of the approach.
The calibration and measurement of bistatic reflectivity at short range (3.3 m) presents challenges that are significantly different from the usual test range measurements (typically monostatic at 100 to 150 m). In order to overcome this an object-free calibration procedure has been applied, eliminating crosstalk, reducing other interferences and removing errors associated with the RCS and alignment of calibration objects. It is based on calibrating the transmitter and receiver antennas as a pair by directing the antennas toward each other. The method thus requires that the antennas can be separated. Furthermore the signal level needs to be handled e.g. by the separation distance or attenuators. The bistatic reflectivity measurements were performed by placing a clutter sample on a turntable which is located at the centre of a bistatic arc. This configuration enables us to do ISAR images. Background contributions were discriminated using a combination of synthetic resolution and zero-doppler filtration. The sensitivity variation across the antenna footprint was handled by calculating an equivalent area from measured off-axis antenna sensitivities. Reflectivities have been measured for a metallic test surface and for grass. The metallic test surface had been manufactured to correspond to typical theoretical bistatic clutter models.
Accurate knowledge of an RFID IC’s input impedance enables the design of performance-optimized RFID tags with a given IC. For this purpose, the most valuable information is the IC’s input impedance at its wake-up power, but as the impedance itself is power-dependent, few simple methods exist to extract this information. This paper presents a method, based on the joint use of computational electromagnetics, wireless RFID tag measurements and Monte Carlo simulations, to determine the input impedance of an UHF RFID tag chip at the wake-up power of the IC and the measurement uncertainty related to the result.