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We introduce a very efficient method for extracting from RCS measurements the cutoff frequency of modes propagating in a waveguide of arbitrary cross section. Based on a model of propagating mode, it offers the capability of identification of mode and it gives also an information about the frequency evolution of the mode excitation amplitude. The effectiveness of this method is illustrated by the analysis of measurements of different shapes of waveguide. The results obtained show that this representation widely improved the performance of time-frequency distributions usually used to analyze this kind of dispersive structure.
Simulated data is presented for a planar array to demonstrate the limitations of planar near-field back projections. It is well known that the result obtained in this way is of limited resolution and accuracy and these limitations are further illustrated through the data presented here. The impact of probe to AUT separation distance is shown as well as the correspondence between array excitation perturbations and that detected through the back projection technique. Results are shown for a simple iterative array excitation adjustment process. The purpose of this paper is to provide guidelines for the application of the planar near-field back projection technique.
This paper presents an accurate method for diagnosis of element failures in large phased arrays. The method is based on the reconstruction of the excitation from measured near-field data by solving the linear system relating the excitation coefficients to the field at measurement points. The dimension of the linear system is reduced by adopting sampling strategies with minimal redundance. The strongly ill-conditioned system is solved using an iterative generalized Landweber algorithm. Numerical simulations on a 2225 elements planar array confirm the effectiveness of the approach.
Analysis of in-orbit phased array antenna patterns measured from earth station requires a considerable examination of the in-orbit antenna operation. The antenna analysis should take into account the constant change of both observation angles and scan angles. The in-orbit phased array antenna pattern characteristics are mathematically analyzed. The coordinate transformation technique to calculate the time-varying trajectory of the observation angle in the antenna coordinate system is presented. The technique also encompasses the satellite track angle calculation as seen from the ground antenna. Data processing procedure of the dynamic antenna patterns and several test issues are discussed.
The electrical phase center locations of the elements in a two-dimensional phased array are examined. A technique is described for precisely locating the element phase centers when the elements are offset from the center of rotation. The element phase centers are shown to be significantly displaced from the physical element locations. The displacement causes a systematic beam pointing bias, which can be predicted and measured.
In this paper, the authors propose an improved Rotatingelement Electric-field Vector (REV) method taking into account amplitude and phase error of phase shifters in order to achieve more precise calibration. The conventional REV method has been used in order to determine and/or adjust amplitude and phase of electrical field radiated from each antenna element -element fieldin phased array antennas. However, amplitude and phase deviations due to phase shifter errors, and so on, reduce the measurement accuracy because the conventional REV method assumes no deviation. On the other hand, the proposed REV method can evaluate element fields without error and error electrical fields -error fields- due to phase shifter errors in each bit, by measuring both amplitude and phase value of array composite electrical field. In a simulation for a 31- element array with 5-bit phase shifter, the evaluated element fields and error fields agree well with the expected values. This result shows that the proposed method allows the phased arrays to be calibrated more accurately as considering phase shifter errors.
A thermal technique for the remote calibration of phased array radar antennas is proposed in this paper. The technique is based on infrared (IR) measurements of the heat patterns produced in a thin planar detector screen placed near the antenna. The magnitude of the field can be measured by capturing an isothermal image (IR thermogram) of the field with an IR imagining camera. The phase of the field can be measured by creating a thermal interference pattern (IR/microwave hologram) between the phased array antenna and a known reference source. This thermal imaging technique has the advantages of speed and portability over existing hard-wired probe methods and can be used in-the-field to remotely measure the magnitude and the phase of the field radiated by the antenna. This information can be used to calibrate the individual elements controlling the radiation pattern of the array.
Although the original reason for creating the Boulder Laboratories of NBS (later known as NIST) was to accommodate the radio program, as described by Dennis Friday and Allen Newell at this conference, the first major program in Boulder was in Cryogenics, which was created in response to a perceived emergency in national security and went on to provide basic cryogenic data to serve the national space program. It was also the origin of programs continuing to the present in the reliability of materials, the thermophysical properties of fluids, and cryoelectronics. The early work at NBS on radio propagation led to the development of new tools for meteorology and became an essential part of the newly formed National Oceanic and Atmospheric Administration. The Joint Institute for Laboratory Astrophysics was formed in collaboration with the University of Colorado and quickly exceeded the field of activity suggested by its name. The Time and Frequency program created a series of radical innovations in frequency standards and the dissemination of time, including a new definition of the meter and an experimental frequency standard based on a single mercury ion.
In practice, accurate VHF Antenna radiation patterns are usually difficult to achieve due to high level multipath present in the measurement test range. Special range geometry’s and source arrangements have been devised over the years [1] to mitigate the measurement errors produced by test range multipath. In this paper we will describe a new illumination source method designed to accurately control the influence of ground path illumination and in turn reduce quiet-zone amplitude ripple. An array of VHF elements with adaptive complex weights will be used to produce a controlled illumination line source for a given range geometry. Simulated quietzone performance will be shown.
This paper describes a High Speed (HS) channel switching capability for an “on-the-fly” data collection scheme primarily intended for use with dual-port probes. A program configures hardware switching of independent channels based on user selections. The switching selects a channel of an antenna (usually a dual-port probe) that is subjected to a continuous switching rate. This rate is carefully linked to the velocity of the scanning axis and the number of sweep points on a Network Analyzer (NWA). Design measures were implemented to take advantage of one of the fastest modes of an Analyzer: a CW sweep. Therefore, precise timing was necessary to ensure that the system is gathering the right datum at the correct time.
We have developed a methodology to determine the quality of a EMC test facility using equipment that may be generally available to RF testing services. By utilizing both the timeand frequency-domains, and accurate picture of the scattering and modal properties of the facility can be determined. This gives a much more information of the facility performance than a traditional scalar, frequency sweep of the facility. While the same frequency information is available with this dual-domain method, the causes of the irregularities can now be determined without guesswork and remediation to the facility can be preformed with more confidence.
Current methods of measuring the electromagnetic properties of materials (i.e., RF shielding effectiveness) include an ASTM (American Society for Testing and Materials) standard test cell and a stripline field applicator, among others. This paper outlines the basic theory of operation of each measurement setup, and compares measured data of similar samples from each setup.
Reflectivities of several commercial absorbers measured at frequencies of 200, 300, 400, 500, and 600 GHz with different incident angles are presented in this paper. The measurements were done using a specially built bistatic test setup with a vector network analyzer and a linear scanner. The presented results show the measured peak reflectance values, i.e., the maximum reflection from the object. The reflectance requirement for absorbers used in compact antenna test ranges (CATRs) is usually –40 dB for all incident angles. According to our measurements, this is not possible with the tested absorbers over the whole frequency range.
A novel broadband dielectric rod probe design that has the characteristics of broad bandwidth; symmetric probe pattern; low RCS; low antenna clutter and dual polarization operation is discussed. The RCS level reduces the interaction between the probe and antenna under test (AUT). The lower antenna clutter level improves the sensitivity in detecting responses from wide angles with greater time delays. During the transmission mode, the rod is excited with a broadband microwave launcher from one end. The radiation then occurs at the other terminal of the rod. Measurement results of the far-field patterns, RCS and reflection coefficient for a prototype rod probe (DRP) are presented.
The level of multiple reflections in near-field antenna measurements is an important issue in a measurement error budget. Traditionally, the interactions between the test antenna and the measuring probe have been reduced by covering the probe mounting structure with absorbing material. In this paper, a novel approach to alleviating the problem is discussed. This implies the use of a skirt to act as a shield against the mounting structure behind the probe, thereby eliminating the need for an absorber, which is a fragile material when exposed to wear and tear. This also has the added advantage that probe calibration data will not depend on a particular absorber that must be considered as an integral part of the probe. With a suitable design of the skirt, the level of multiple reflections can be reduced, whilst at the same time maintaining the pattern of the probe in the boresight direction unchanged. Prototypes of probes for 20 GHz and 30 GHz have been manufactured and tested, and excellent agreement between experimental results and theoretical predictions has been observed.
High growth in the mobile telephone industry is forcing the development of new terminal antennas at an everincreasing pace. The future multi-standard telephones demand antennas that need to be designed and tested for a variety of radiation and bandwidth specifications. New wireless communications devices, such as those using the new Bluetooth and IEEE 802.11 standards, will require testing of a whole range of new products containing antennas, such as computers, household appliances and consumer electronics. The radiation characteristics of the small antennas used in such devices are strongly dependent on the environment into which they are radiating. For example, the presence of the operator or the mounting and positioning equipment of a test set-up can severely change their radiation characteristics. etenna Corporation addresses this problem by employing a Satimo spherical near-field test system. This system allows for rapid, and in some cases, real-time observation of in situ antenna patterns. A brief description of the test facility is presented in this paper along with sample data.
The need to measure the boresight pointing direction of radar antennas to a high degree of accuracy yields a requirement for excellent positioning accuracy on near-field antenna ranges. Evaluation of this requirement can be accomplished by a full and complete sensitivity analysis. Alternatively, to gain an understanding of the effects of errors more simply, one can approach the question of accuracy required in the setup, by use of a physical model and straightforward physical reasoning. The approach starts with the assumptions of a collimated wave with planar phase fronts and the premise that the boresight direction of such a sum beam is along the normal to the phase fronts. A sensitivity analysis of the simple trigonometric boresight relationship between mechanical boresight and phase front normal, shows how accurate the receiver and the positioner must be to achieve a given boresight determination. Such an approach has been known for many years as it regards planar scanning; and, the results are known to be applicable. In this paper this consideration is extended to spherical scanners to arrive at estimates of the mechanical positioner accuracies and electrical receiver accuracies needed to make boresight measurements of radar antennas with spherical near-field ranges.
A series of experimental and theoretical tests designed to develop techniques for reliable computational modeling of automobile antenna performance is presented. The results from the experimental measurements are compared with the results of computational techniques to verify their accuracy and reliability. The Electromagnetic Surface Patch (ESP5) code, a theoretical Method of Moment (MoM) general-purpose code developed at the Ohio State University, is used for computational modeling. We progress from the simple geometry of a single square plate and a monopole, to the more complex structure of a small copper-coated plastic model of an automobile. The computational simulation and measurements are configured with both a monopole antenna mounted at the center of the automobile roof and a backlite heater grid FM antenna. The input impedance, pattern, and polarization are all measured. Comparisons between the results of the computational simulations are presented, as well as the procedures used to measure the antenna characteristics and compare the experimental data with the measured data.
A new 3-dimensional measurement method for the determination of the radiated power of mobile phones is presented. In contrast to usual 2D cut plane measurements, the 3D method gives the whole 3D radiation pattern. From this, insight into the detailed angular dependent radiation characteristics can be derived, which is very useful for mobile phone manufacturers and antenna developers. Furthermore, the overall radiated power as well as the directivity of the mobile phone can be post processed from the measured data. A very interesting feature is the ability of the measurement set up to carry a phantom head. With it, measurements of the whole system user and mobile phone can be performed to study the user's influence. The measurements are carried out in an EMC anechoic chamber, which has been specially optimized regarding reflection absorption. Some examples demonstrate the comprehensive measurement capabilities of the presented method.
In this paper, a three-covered monopole array antenna with 155o phase-shift and 0.1 ë spacing was suggested to give a minimum power radiation in the direction of the mobile user’s head, consequently the hazard that may the EMW inflects on the human health can be considerably reduced. Several experiments were conducted in this work to measure the power radiation pattern of the monopole, as a common antenna used in mobile telephones, and the three-element array antenna in free-space and with human head adjacent to the antenna. The frequencies were chosen to be 1800 MHz and 1985 MHz, for uncovered and covered designs, respectively, to cover the GSM-1800, PCS-1900, and DECT frequencies. A dielectric material with år = 2.33 , tanä = 0.0005 , and thickness equal to the radius of the monopole was used to cover each array element. It was found that the length of the covered monopole is about 90% of the uncovered length. A practical method was suggested in this work for attaching the adopted array to the mobile telephone.