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The DREO-DFL Antenna Research Lab (DDARLing), contains far-field and planar near-field antenna measurement ranges. Measurements can be made on both ranges from 1.0 to 62.5 GHz. In the early implementation stages of our antenna measurement ranges, most of our energy was absorbed in mastering the mechanics of the positioners and the intracies of the operation of the software, and addressing component failures. To make useful measurements, it is necessary to minimize system errors. Early experience and frustration has led us to the development of an ordered series of standardized procedures that are aimed at careful set-up, calibration, and operation of the ranges. Within these procedures, attention is paid to the identification and minimization of errors due to alignment, equipment calibration, linearity, leakage, multipath, and drift. Following a brief description of the two ranges in the DDARLing facility, the paper provides details of one of these procedures.
This paper presents a design of dual shaped reflector feed system suppressing cross polarized components for compact antenna test range(CATR). This system consists of a parabolic main reflector, two shaped reflectors and primary horn. As for co-polarization characteristics, these subreflectors are shaped to achieve a plane wave with uniform amplitude in a test zone. As for cross polarization characteristics, cross polarized components are eliminated in following way. An initial reflector system before shaping is satisfied with a condition of eliminating cross polarized components based on a beam mode expansion technique. This condition needs more than three quadratic reflectors, and frequency independent design can be derived. In this paper, the effect of higher order modes are considered. When shaping reflectors, however, additional cross polarized components are generated and the condition of eliminating cross polarized components is not satisfied. In this paper, a correction method of the cross polarization is also presented. A design result shows that the system has a test zone of 2.5m diameter and in test zone, lower ±0.5dB amplitude ripple, ±4.5° phase ripple and lower -44dB are achieved.
Scientific-Atlanta has recently begun work on a large 55 ft.(W) x 45 ft.(H) compact range reflector. The reflector is a Model 5738 with a 45 ft. focal length and a 38 ft. diameter by 38 ft. long cylindrical quiet zone. Due to the large size of the reflector, it is necessary to form the surface as several large, independent sections and assemble and align the reflector at the installation site. The 5738 reflector is shown in Figure 1 with the 38 ft. quiet zone superimposed. Figu re 1. Front View of 5738 Reflector Showing Sections The independent and predictable behavior of large sections proves to be very beneficial for performing an electrical alignment of the reflector based on field probe phase data. This paper discusses the required alignment tolerances and analytic tools developed to predict the effects on quite zone performance due to alignment errors in the sections of the reflector.
The ESA Compact Payload Test Range (CPTR) has been designed to allow scanning of the range axis by means of the movement of the feed in the focal region. This capability has been applied to the verification of the performance of the Inter Orbit Link Antenna (IOLA) signal acquisition and tracking system, known as the IAPS, of the ARTEMIS communication satellite. The feed of the CPTR was used to simulate the Ka band signal transmitted from a low earth orbit satellite. The paper describes the test scenario and requirements, as well as presenting the scan performance of the ESTEC CPTR. The scan performance was verified by comparing azimuth scanned patterns of the main beam with those made translation of the feed in the focal region.
This paper presents a new technique for performing range compensation of full sphere antenna patterns measured on fixed line-of-sight antenna ranges where pattern measurements are made over a spherical surface. Such ranges include far-field, compact, and spherical near-field ranges. A plane wave model of the range field illuminating the antenna under test (AUT) is determined as described in another paper. This plane wave model consists of a small, selectable number of plane waves. Equations are given describing the transformation of range coordinates to AUT coordinates. This allows the response of an AUT to a plane wave from an arbitrary direction to be defined using only the far-field pattern of the AUT. The error pattern added to the pattern measurement by the extraneous plane waves is then estimated using the plane wave model and the measured pattern. This error pattern is subtracted from the antenna pattern measurement to obtain a compensated pattern. The compensated pattern and error pattern are improved iteratively. This paper demonstrates the technique using simulated data. The rotation of the spherical AUT grid with respect to the range grid during the measurement requires an interpolation of the measured fields to estimate the error pattern. Investigations of interpolation error are presented. The computational complexity of the compensation algorithm, excluding the plane wave model, is on the order of the number of measurement points on the spherical measurement grid. K
Cellular and PCS basestation antennas are basically arrays with highly directive elevation patterns and broad azimuth patterns. This causes measurement problems because they are large but not directive in both principal planes. As a result, the pattern measurements of these antennas that have been performed outside have been unreliable in many cases because they are very receptive to interference and range clutter. Thus, one wants to move inside but the antenna size can significantly impact the overall range cost. This paper describes a very practical solution to this problem. Since basestation antennas are long and narrow, one can use a near field scanner approach to deal with the length. In fact by using a sectorial horn probe, the narrow dimension of the antenna-under-test is illuminated by a cylindrical wave. Thus, the scanner need only probe the field along the antenna length. This linear scan data can then be transformed to generate the desired far field elevation pattern. The details of this novel design will be described as well as the results, to illustrate the system capability and accuracy.
As part of the 1997 Automated Highway System Demonstration, the Ohio State University ElectroScience Laboratory (OSU/ESL) developed and operated a pair of automobiles equipped with radar systems for steering and cruise control. In a national demonstration attended by six autonomous vehicle teams, the system was used to convoy three autonomous vehicles along a 7 mile stretch of closed highway lanes near San Diego. The goal of the look ahead radar system was to acquire and track the vehicle ahead.
The Ohio State University ElectroScience Laboratory participated along with the Center for Intelligent Transportation Research as one of six teams to demonstrate an automated highway concept at the National Automated Highway Demo at San Diego in August, 1997. The forward looking radar concept which was demonstrated used the FSS highway stripe which was presented at the 1995 AMTA Meeting. This paper describes the radar system as implemented for automated guidance, and presents measured results on the system antenna array and on the system itself. In addition, results of the demonstration in San Diego will be discussed. The radar used a monopulse guidance architecture, where the amplitude from left and right receive antennas are subtracted, and then divided by the sum of the left and right antennas in order to provide a normalized steering error signal. The antenna array used a single transmit horn, and a matched pair of receive horns, all vertically polarized. All three antennas were nestled into the composite front bum per beam, looking out through a foam radome panel about the size of a license plate. Performance data on the antennas and the steering sensing information will be presented. The radar system was a chirp radar covering a frequency spectrum of 10 to 11 GHz. The narrow frequency of the FSS radar stripe occu rred at 10.95 GHz, allowing its signature to be distinguished from the return of vehicles and other objects out in front of the vehicle. Radar system measured results in the highway situation will be presented, and its performance in San Diego will be discussed.
In this paper we will compare different techniques that can be used to measure the performance of automobile antennas. The use of indoor scale-model and outdoor full-scale range measurements will be discussed. These rangetype techniques characterize the engineering parameters of the antenna using signals with well defined polarizations and angles of arrival. These techniques are important in the initial stages of the antenna development. In the final stages of automobile antenna development, it is important to know how well the antenna will perform in the "real-world". We have developed mobile measurement techniques that use commercial off-the-air signals to characterize the performance of the automobile antenna in the real-world environment. We will describe three different systems that were developed to measure the performance of AM/FM, cellular, and GPS antennas.
Until now the mobile phones have been qualified by power measurement at the RF-connector of the handset without any regard to the antenna characteristic and the losses caused by the mismatch of the impedance matching network. IMST is exammmg, via measurements, the user's influence on the antenna pattern of the mobile phone. These measurements were performed in the transmit situation and in the receive situation of the mobile phone at different elevation angles and for different channels of the German E Plus-Network. Due to the differences between human bodies and due to the body's movement during a measurement, the emphasis of this investigation was on the development of a model with dimensions and electromagnetic characteristics similar to those of the average human body. By comparing measurement results using different test persons and the model, the validity of the model has been evaluated.
A general approach for phase-retrieval is discussed. The representation is based on an advanced non-redundant sampling representation and is able to explicitly take into account geometrical characteristics of the source, like the overall dimension and the general shape, as well as a priori inforn1ation on the near-field and far-field.
A technique was developed to recover the near-field function on a larger data set than the one that is measured. It requires the preliminary determination of functions containing the information relating the two data sets. The simplest way of obtaining such a function is to measure the near-field function on the larger and the smaller data set. This seems to be a drawback to the technique. However. after making one such pair of measurement it is therefore non necessary to do so again and the field of the antenna can be obtained, from the smaller data set measurement, with comparable accuracy. The technique is somewhat different when compensating for a sampling rate reduction. However, in both cases an analytical extension is required to fill the desired domain of definition, followed by a division. In the case of the sampling area the division of the spectral functions f2 by f1 is made in the spectral domain while in the case of the sampling rate the division of the near-field functions E' by E is made in the near-field domain. An experiment was performed to demonstrate the applicability of the above technique. A full near-field measurement of a linear array antenna was performed and processed, then after displacement of the antenna, measurements were done, in one case, on a truncated smaller scan area, and in another case with a larger sampling interval. The technique was applied to recover the complete far-field characteristics of the antenna from the smaller data set. The far-field characteristics of the antenna obtained by this technique were shown to be very similar to the results obtained from a more complete near field measurement.
A method is presented for computing far field antenna patterns from spherical near field antenna measurement data. The new method utilizes a novel Uniform Geometrical Theory of Diffraction (UTD) based transformation of spherically scanned antenna tangential electric (or magnetic) near field measured values to more efficiently obtain the antenna far field. Examples illustrating the accuracy and speed of UTD based spherical near to far field transformations for large to moderately large antennas are presented.
Phase space representation (PSR) is introduced as a diagnostic tool for near-field antenna measurements. The PSR of a linear scan is defined as a two dimensional function of position and wavenumber. This combined spatial-wavenumber distribution can reveal features which are not directly visible in either spatial- or wavenumber-domains. It is shown that PSR is useful for both error diagnostic and compensation of certain errors. In particular, the benefits of PSR in identifying aliasing, spatial errors, multiple AUT-probe reflections, and random errors in amplitude and phase will be demonstrated. The capability of the PSR in compensation of contaminated measurements is demonstrated by examples.
The far-field parameters of an antenna are obtained from near-Field measurement with an accuracy that is limited by the sampling area and the sampling rate used to collect the measurement data. It is therefore important to know the relation between the far-field parameters and the sampling parameters. A parametric study of the far field parameters accuracy versus the sampling parameters was made. In order to determine the optimal choice of the sampling parameters to achieve the desired far-field accuracy, planar near-field measurements of a linear array were performed in an anechoid chamber at the Canadian Space Agency. A program performing Fast-Fourier Transform was used to process the data and to obtain spectral domain and reconstruct the far field patterns. A methodology developed in [1] was used to compare different spectral and far field patterns obtained from different sampling conditions. Parametric curves were developed for the far-field parameters such as gain, beam pointing, beam width, sidelobes, etc.
The new EMC-standards in Europe have strengthened the requirements for test facilities. In this paper examinations are concentrated on anechoic chambers, which are mostly used for measuring radionoise emissions. To become accredited a chamber have to own excellent performance, which is only possible by excellent absorbers and a careful choice of the measurement axis. A program for the evaluation of anechoic chambers has been developed and recently extended to permeable materials. This allows the calculation of chambers equipped with ferrite tiles or even a combination of ferrite and foam absorbers. Furthermore the numerical code is a very helpful tool during the planning phase of a chamber and offers the possibility to find the best way to improve the performance of older chambers. To estimate the performance the results are compared to the field distribution in an ideal Open Area Test Site (OATS).
We review the development and recent performance results of a stand-alone fiber optic based EM field sensor system. The sensor heads are miniature (lcm), electrically passive, and are directly coupled to optical fibers at the remote sensing site. Sensor conversion of EM fields to optical intensity is carried out by mounting small antenna structures directly onto high speed lithium niobate electro-optic modulator chips. Optical power to the sensor head is derived from a stabilized laser which is located within a system chassis at a control room location. Sensor and fiber temperature drift effects are compensated by specialized remote bias control electronics. Recent broad spectrum tests have demonstrated a system bandwidth of about 20 GHz, and a minimum detectable field in the lO's of mV/m. Ultra wideband pulse measurements have demonstrated real time pulse signals of about 2 Vpp for 3 KV/m fields. The sensor system is slated for application in EMI effects such as EM compatibility, and for pin-point near-field and far-field mapping of radiation patterns. The technology is readily scaleable to frequencies exceeding 20 GHz.
Mode stirred chambers are used to perform radiated susceptibility tests on equipment that is expected to operate normally when exposed to electromagnetic (EM) fields. These tests are useful in identifying failure events in airborne equipment, medical equipment, and other electronic equipment that are exposed to EM fields. The two major methods of modal excitation are mechanical mode stirring and frequency stirring. The majority of reverberation chamber tests are done using the mechanical method. Mechanical mode stirring is the process of varying boundary conditions in a complex cavity to ensure that devices in the cavity are exposed to an isotropic and randomly varying electromagnetic field. This is analogous to an amplitude modulated signal, which would consist of a carrier with random amplitude and phase. An analysis of the frequency content of the energy around the carrier is performed, and the effects of this frequency spread on the use of mode stirred chambers for testing is investigated. The understanding of this frequency spread is important in quantifying upsets of equipment in the chamber. Examples of different rotation rates and the corresponding frequency spectra are examined.
This paper presents a measurement system used for W-band complex permittivity measurements performed in NASA Langley Research Center's Electromagnetics Research Branch. The system was used to characterize candidate radome materials for the passive millimeter wave (PMMW) camera experiment. The PMMW camera is a new technology sensor, with goals of all-weather landings of civilian and military aircraft. The sensor was developed by TRW as part of a cooperative agreement for the Defense Advanced Research Projects Agency (DARPA) and the dual-use technology program. NASA Langley manages the program on behalf of DARPA and also supports the technology development and flight test operations. Other members of the consortium include McDonnell Douglas, Honeywell, and Composite Optics, Inc. The experiment is scheduled to be flight tested on the Air Force's "Speckled Trout" aircraft in late 1997. This paper details the design, set-up, calibration and operation of a free space measurement system developed and used to characterize the candidate radome materials for this program.
With the progressive increase in computer capabilities, programming environments other than text based development environments have become possible and popular. Specific to the area of data acquisition and control two prominent graphical programming environments have emerged; LabVIEW and HPVEE. These environments provide graphical icons or components to be used as building blocks for the development of sophisticated and powerful systems and allow the developer to concentrate on the "flow of data" and the functions within the application and not the syntax and procedural control required of text based systems. At the David Florida Laboratory, a project as been initiated to upgrade the current antenna measurement environment from a text based (HP-Basic) software system with a limited user interface to a more sophisticated and complex graphical user environment using the LabVIEW graphical programming environment. This paper presents a study of the use of graphical environments for developing antenna measurement and test systems. Details of the overall project development, design considerations, profile studies and project conclusions are described. This paper also presents the basis of a toolset comprising of metrics and measurements developed and performed during this project to aid in the design and development of future projects using graphical environments at the David Florida Laboratory.