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This paper describes the extrapolation measurement method for determining gain of directive antennas at quasi-near-field distances. It is based on a generalized threeantenna approach and therefore does not require a priori knowledge of the antennas. It has been used at the National Institute of Standards and Technology (NIST) for over twenty years to calibrate antenna gain standards within 0.1 dB. The basic theory, measurement procedure, data analysis, and sources of uncertainty for the extrapolation gain measurement will be presented.
A networked antenna measurement system based on Intranet technologies allows users to undertake different aspects of the measurement process (data acquisition, instrument control and analysis) remotely. It also allows for the efficient transfer of data between different nodes on the network. At the David Florida Laboratory, a project is currently underway to upgrade the antenna measurement system to a graphical user interface (GUI), developed in the LabVIEW Version 5.0 environment. Integral to this upgrade is the development and implementation of data analysis applications and a network based on Intranet technologies. The antenna measurement software application functions over the Intranet as a clienUserver model, which is designed to support a number of clients functioning concurrently on different machines. The design of the network permits use of a single server providing the control and interface between a client operation i.e. the test conductor and the data acquisition system. This paper describes the steps taken thus far to upgrade the antenna analysis software and provide an overview of the client server architecture developed and implemented using LabVIEW.
Dual gridded, shaped reflector antennas have been designed, manufactured and measured respectivily by ALENIA, AEROSPATIALE Les Mureaux and ALCATEL for the EUTELSAT "W" satellites program. The tight requirements, for coverage gain and cross-polar discrimination together with in-coverage cross-polar level less than 44 dB below the peak, required sophisticated techniques for design and measurements. ALENIA used optimisation and prediction techniques, which took into account thermal deformation effects and the multi-layer structure of the assembled dual gridded antennas. The optimisation process led to high performance antennas associated with the complex surface shapes. Moreover, including the actual manufactured reflector surfaces in the analysis, an excellent correlation between measurements and predictions have been obtained. Measurements were performed in the Alcatel Space Industries Compact Antenna Test Range in Cannes. ALCATEL invested into high polarisation purity illuminators and special hexapod tools in order to efficiently optimise the assembled antenna performance. The measurement optimisation process led to antennas which all met their requirements.
The Seeker Test and Evaluation Facility (STEF) located on Range C-52A at Eglin AFB FL. is used to perform high-resolution multispectral (EO-IR-RF-MMW) signature measurements of US and foreign ground vehicles primarily to support the Research, Development, Test and Evaluation (RDT&E) of smart weapons (seekers, sensors and Countermeasure techniques). In order to support two major DOD signature measurement programs in 1997 this facility required significant range upgrades and enhancements to realize reduced background levels, increase measurement accuracy and improve radar system reliability. These modifications include the addition of a 350'X 120' asphalt ground plane, a new secure target support facility, a redesigned low RCS shroud for the target turntable and a new core radar system (Lintek elan) and data acquisition/analysis capability for the existing radars Millimeter-Wave Instrumentation, High Resolution, Imaging Radar System - MIHRIRS). This paper describes the performance increase gained as a result of this effort and provides information on site characterization and radar instrumentation improvements as well as examples of measured RCS of typical ground vehicle signatures and ISAR imagery
Full polarimetric scattering measurements are increasingly being required for radar cross-section (RCS) tests. Conventional co-and cross-polarization calibrations fail to take into account the small amount of antenna cross-polarization that will be present for any practical antenna. In contrast, full polarimetric calibrations take into account and compensate for the cross-polarization the calibration process. We present a full polarimetric calibration procedure and a simulation-based performance study quantifying how well the procedure improves measurement accuracy over conventional independent channel calibration.
The use of dual polarization in meteorological radars offers significant advantages over single polarization. Recently a standard single-polarization Cuband radar was upgraded to operate in dual-polarization mode. The antenna has a 4.2m diameter parabolic reflector with a prime-focus feed. A spherical Fresnel-zone holographic technique was used to obtain the radiation pattern for the upgraded antenna. The sidelobes were higher than predicted and so the data was analyzed to identify the relative contributions of shadowing from the feed crook and surface errors in the dish. This paper describes practical considerations in the measurement of this antenna and the analysis of the results.
Three common methods of measuring circularly antennas on a far-zone range are: using a spinning linear source antenna (SPIN-LIN), measuring the magnitude and with a linearly polarized source antenna in two orthogonal positions (MAG-PHS), and using a circularly polarized source antenna (CIRC-SRC). The MAG-PHS and CIRC-SRC methods are also used in a near-field or com pact range. The SPIN-LIN method is useful because an accur te measurement of the axial ratio and gain can be made without the need to measure phase. The MAG-PHS method is the most general method and can also completely characterize the polarization of the test antenna. The CIRC-SRC method is the simplest and least time-consuming measurement if the antenna response to only one polarization is needed. The choice of measurement method is dictated by schedule, accuracy requirements, and budget. An analysis is presented that provides errors in the measured gain, relative gain pattern, and phase of the test antenna depending on the polarization characteristics of the source and test antennas. These results are useful for deciding which measurement method is the most appropriate to use for a particular job. These results are also useful when constructing more complete error budgets.
DATE is a portable, rapid assembled, planar near field measurement system for ERIEYE Airborne Early Warning System. DATE shall be used both as a production range at Ericsson Microwave Systems (EMW) and as a maintenance equipment delivered with the ERIEYE AEW System. Up to now ERIEYE has been measured and phase aligned at EMW's large nearfield range. The active antenna is interfaced through a Beam Steering Computer (BSC) and hardware interface. The disadvantages with this approach is a slow communication speed and reduced Built In Test. Since the large nearfield range is designed to meet the requirements from many different antenna types the transport, mounting, alignment and range error analysis are very time and personnel consuming. The DATE-scope is to provide a portable planar near field test system that's custom-made for ERIEYE. The time from stored system to completed measurement shall be very short and performed by a "non antenna test engineer". This is done by: • Incorporate the BSC as a radar-mode. • Use the radar receiver and transmitter for RF measurement. • Reduce alignment time and complexity by a common alignment system for antenna and scanner. Scanner alignment for very high position accuracy. • Automatic Advanced Data Processing: Transformation from near field to far field to excitation to new T/R-module setting-up-table in one step.
Practical antenna applications require accurate characterization of the antenna, including both the amplitude and phase performance. Recent advances in antenna measurement technologies allow the antenna to be measured in various indoor facilities with a well controlled environment. However, measurements that take a long time to complete can still suffer phase drift and variation due to the movement of RF cable as well as changes in the chamber environment. Without proper phase correction, the measured antenna pattern performance may not satisfy the desired requirement. Consequently, it is very important to have appropriate methods for phase correction in order to obtain more accurate results. In this paper, a simple procedure for phase correction of volumetric spherical near field antenna measurement is presented. In this method, only a few additional measurements are needed for correcting the phase variation observed in the original volumetric pattern. Application of the phase corrected pattern has been found to satisfy the desired antenna performance.
Calibration of monostatic radar cross section (RCS) has been studied extensively over many years, leading to many approaches, with varying degrees of success. To this day, there is still significant debate over how it should be done. It is almost a certainty, that if someone proposes a way to calibrate RCS data, someone else will come up with reasons as to why the "new" approach will not yield results that are "good enough." In the case of full scattering matrix RCS measurements, the lack of information concerning calibration techniques is even greater. The Air Force's Radar Target Scattering Facility (RATSCAT) at Holloman AFB, NM,has begun an effort to refine monostatic and bistatic cross polarization measurements at various radar bands. For the purposes of this paper, we have concentrated on our monostatic cross polarization developments. Such issues as calibration targets and techniques, system stability requirements, etc. will be discussed. During several programs we have attempted to collect sufficient data to do full scattering matrix corrections. In a previous paper, "Bistatic Cross-Polarization Calibration," our collected data had a high background which obscured much of the cross polarized return. The data presented here is from a program conducted at RATSCAT recently which utilized the Ka band. Because of the sensitivity of measurements at Ka to many effects, an error estimate was required. This paper presents this error estimation and some results of full scattering matrix correction of RCS data. This analysis is based upon "The Proposed Uncertainty Analysis for RCS Measurements", NISTIR 5019, by R. C. Wittmann, M. H. Francis, L. A. Muth and R. L. Lewis. This paper was aimed at principle pole measurements, e.g. HH and VV. The tabular data presented in the paper are from this paper with additions for errors associated with cross polarization and cross polarization correction.
In the last few years, a change has occurred in the RCS metrologist concerns for error analysis and the quantification of measurement uncertainty. The specific methods for range characterization and uncertainty estimation are the topics of many passionate technical discussions. While no single treatment can please everyone, most agree a measurement uncertainty program is critical to the understanding of measurement quality, the development of error reduction strategies, and to the planning of range improvement paths. We present the statistical case for the natural grouping of errors into multiplicative and additive classes. We will derive the two cases where one class dominates as presented by LaHaie [1], and then expand the analysis to include the general case of competing classes. We summarize the role and applicability of this method in estimating measurement quality and discuss how this procedure offers a logical and comprehensive error propagation solution to both top-down and bottom-up range characterization approaches.
Calibration standards for radar systems are being developed cooperatively by NIST and DoD scientists. Our goals are to develop standard procedures for polarimetric radar calibrations and to improve the uncertainty in the estimation of system parameters. Dihedrals are excellent polarimetric calibration artifacts, because (1) the consistency between dihedral scattering data and the mathematical model of scattering can be easily verified, and (2) symmetry properties of the dihedral data provide powerful diagnostics to reveal system problems. We apply Fourier analysis to polarimetric data from dihedrals over a full rotation about the line of sight to reduce the effects of noise and clutter, misalignment, and other unwanted signals. An extension of the analysis to satisfy nonlinear model constraints allows us to monitor data quality and to further improve the calibration. We obtain the system parameters from the Fourier coefficients of the data in a simple manner. We illustrate these concepts using polarimetric radar cross section calibration data obtained as part of a national interlaboratory comparison program.
A computer simulation for prediction of equivalent system temperature is presented. The figure-of-merit for a receiving system is given by the ratio of the receiving system gain by the equivalent system temperature (G/Ts). While the gain, G, can be well characterized by laboratory measurements, measurements of system temperature, Ts, taken in the laboratory do not correspond well to measurements in outdoors, due to a myriad of environmental factors. A computer methodology to statistically characterize the noise performance of a satellite earth station receiver in the operational environment was developed for the Department of Commerce National Institute for Standards and Technology, as of a Small Business Innovation Research contract. The result of Phase 2 of the SBIR is an implementation of this computer methodology called the Receiving System Analysis Tool. This paper describes the methodology, the RSAT simulation, and its application to SATCOM terminal analysis.
This paper is concerned with the measurement and analysis of a circularly polarized, flat plate patch array receiving antenna at 12.5 GHz. Input impedance and far field pattern measurements of the antenna over the frequency band from 10 to 15 GHz were performed. The small Compact Range (CR) facility of the Ohio State University Electro Science Laboratory OSU/ESL was used to measure the gain pattern. Gain pattern measurement of the antenna was done by using the gain comparison method. A broadband (2-18 GHz), constant phase pyramidal horn antenna was used as a reference. The data were analyzed to determine the radiation efficiency of the antenna.
In a networked antenna measurement laboratory implementing Intranet technologies provides significant benefits. Some of the benefits include efficient data transfer, remote test setup, remote monitoring and control and ease of data analysis. This paper first summarizes some of the options available and considerations in incorporating an Intranet architecture in an antenna measurement laboratory. Relative merits and pitfalls of some of the solutions are discussed. Performance issues and tradeoffs are outlined. The David Florida Laboratory (DFL) RF Facility experience in implementing an Intranet based operation is presented.
During the design of spacecraft antennas a well defined geometrical configuration of antenna components is supposed. Also the requirements for the accuracy of the antenna integration normally will be given. The antenna alignment processes have to ensure, that the designed configuration with the required accuracy can be met. Additionally the antenna pointing has to be determined with respect to the RF measurement facility. In this paper the concepts are treated, how to determine the actual and the designed orientation and location of the components of the space antennas during subsystem and system level integration and tests. This includes also the definition of needed references for the antenna components, the creation and application of coordinates or orientation matrices at manufacturing or integration level, the used coordinate systems and the attainable accuracy for different methods. For the evaluation of the RF pattern performance, the correlation between the spacecraft coordinate system and the facility coordinate system has to be known. Basic principles of this pointing alignment and an error analysis of the measurement accuracy will be explained. The presented concepts are based on the experience at DSS' test facilities with various antenna types and agreed with different antenna manufacturers and customers.
The objective of this study is to evaluate the measurement errors of a near-field range at in order to develop some techniques to minimize them. Measurements were performed on a standard gain horn as references. The methodology presented demonstrates that it is feasible to calculate the far-field radiation from near-field measurement with one deconvolution that will include all the errors introduced by the instrumentation
A development work of a 2.4 m x 2.0 m hologram for testing the 1.1 m offset reflector of the Odin satellite at 119 GHz is reported. The analysis of the hologram is based on physical optics (PO) and finite difference time domain method (FDTD). The hologram is fabricated with an etching process. A comparison between the theoretical and measured quiet-zone fields of the hologram type of compact antenna test range (CATR) is made.
Sanders, A Lockheed Martin Company, measures radar cross section (RCS) and antenna performance from 2 to 18 GHz at the Com pany's Compact Range. Twelve feed horns are used to maintain a constant beam width and stationary phase centers, with proper gain. However, calibration with each movement of the feed tower is required and the feed tower is a source of range clutter. To Improve data quality and quantity, Sanders and The Ohio State University ElectroScience Laboratory designed, fabricated, and tested a new wide band feed. The design requirement for the feed was to maintain a constant beam width and phase taper across the 2 - 18 GHz band. The approach taken was to modify the design of the Ohio State University's wide band feed [1]. This feed provides a much cleaner range which reduces the dependence on subtraction and other data manipulation techniques. The new feed allows for wide band images with increased resolution and a six fold increase in range productivity (or reduction in range costs). This paper discusses this new feed and design details with the unique fabrication techniques developed by Ohio State and its suppliers. Analysis and patterns measured from the feed characterization are presented as well. This paper closes with a discussion of options for further improvements in the feed.
A sophisticated software package FARANA (FAR-field ANAiysis) is presented for transforming planar near-field test data to far-field antenna patterns, including enhanced analysis of far-field results. FARANA is coded in MATLAB version 5.0. MATLAB (MATrix LABoratory) is an interactive mathematical modelling tool based on matrix solutions without dimensioning. Using MATLAB, numerical engineering problems can be solved in a fraction of time of time required by programs coded in FORTRAN or C. FARANA operates with a state-of-the-art graphical user's-interface, is intuitive to use and features high speed and accuracy. This paper addresses an assessment of the program, discusses its use and enhanced far-field analysis capabilities.