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This paper presents a brief overview of ANSI/NCSL standard Z-540 (1). Z-540 offers a straightforward way to organize range documentation. We discuss the major points and sections of Z-540, and how to organize a format-universal "range book". Since Z-540 is the US equivalent of International Standard (ISO) 25, it is especially useful for two reasons; (1) it is applicable to Radar Cross Section (RCS) ranges and (2) its quality control requirements are consistent with the ISO 9002 series of quality standards. Properly applied, Z-540 may greatly improve the quality and consistency of RCS measurements produced, and reported to range customers.
The National Institute of Standards and Technology (NIST) is coordinating a radar cross section (RCS) interlaboratory comparison study using a family of standard cylinders developed at Wright Laboratories. As an important component of measurement assurance and of the proposed RCS certification program, interlaboratory comparisons can be used to establish repeatability (within specified uncertainty limits) of RCS measurements within and between measurement ranges. We discuss the global importance of intercomparisons in standards metrology, examine recently conducted comparison studies at NIST, and give a status report on the first national RCS intercomparison study. We also consider future directions.
Calibrated radar images are often quantified as radar cross section (RCS). This interpretation, which is not strictly correct, can lead to misunderstanding of test target scattering properties. To avoid confusion, we recommend that a term such as "scattering brightness" (defined below) be adopted as a standard label for image-domain data.
Transferring data from a measurement facility to other internal or external users of the data are often troublesome. In this paper we present a data file format which is independent of platform, operating system and programming. Thus it is very suitable for simplified exchange of data. The format is described and a simple example is given how to read and write data in a file. With this paper we would like to promote further development and use of this format in the antenna measurement society.
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. In the case of bistatic RCS measurements, the lack of information concerning calibration techniques is even greater. This paper will present the results of a preliminary investigation into calibration techniques and their suitability for use in the correction of cross-polarization errors when data is collected in a bistatic configuration. Such issues as calibration targets and techniques, system stability requirements, etc. will be discussed. Results will be presented for data collected in the C and X bands on potential calibration targets. Recommendations for future efforts will also be presented.
This paper describes the current status of the present cylinder family, and introduces theoretical and experimental RCS data for a modified "bicone" calibration standard. These standards, when used appropriately, greatly improve the quality and efficiency of primary RCS calibration measured within indoor or outdoor ranges. These techniques should offer range owners fairly simple methods to monitor the quality of their primary calibration standards at all times.
The National Institute of Standards and Technology (NIST) is coordinating a radar cross section (RCS) interlaboratory comparison study using a rotating dihedral. As an important component of measurement assurance and of the proposed RCS certification program, interlaboratory comparisons can be used to establish repeatability (within specified uncertainty limits) of RCS measurements within and among measurement ranges. The global importance of intercomparison studies in standards metrology, recently conducted comparison studies at NIST, and the status of the first national RCS intercomparison study using a set of cylinders are discussed in [1]. In a companion program, we examine full polarimetric calibration data obtained using dihedrals and rods. Polarimetric data is essential for the complete description of scattering phenomena and for the understanding of RCS measurement uncertainty. Our intent is to refine and develop polarimetric calibration techniques and to estimate and minimize the correstponding measurement uncertainties. We apply theoretical results [2] to check on (1) data and (2) scattering model integrity. To reduce noise and clutter, we Fourier transform the scattering data as a function of rotation angle [2], and obtain the radar characteristics using the Fourier coefficients. Calibration integrity is checked by applying a variant of the dual cylinder calibration technique [3]. Future directions of this measurement program are explored.
Ell has been extensively involved in the development of advanced processing techniques (APT) to improve the quality and utility of both indoor and outdoor RCS/ISAR measurements. These include algorithms for removal of clutter, RFI, and targetsupport contamination (including interactions), prediction of far field RCS from near field measurements, suppression of multipath contamination, and extraction of scattering features/components. These techniques have been implemented in a framework based on ERIM International's IMGMANIP signal/ image processing toolbox and stream input-output (SIO) data flow paradigm. This paper describes a recently-developed Graphical User Interface (GUI) which incorporates the most mature and frequently-used APT algorithms.
Based on the method of moments (MoM), a network model algorithm perturbs the linearized electromagnetic interaction model (the admittance matrix) of a simulated target to match an actual measured data set in the least squares sense, resulting in a more accurate interaction model for the physical target. Since the admittance matrix is independent of source location this technique is amenable for use as a near field to far field transform algorithm. In this ansatz, a MoM admittance matrix is perturbed to match a set of near field measurements, then the far zone field is predicted using the perturbed admittance matrix multiplied by the appropriate far field measurement vector. This paper describes the application of the MoM network model technique to measured and numerical data for ten and twenty wavelength conespheres. Initially, a discussion is given of the code modifications necessary to adapt JRMBOR for network model use. A validation is then provided using "perfect" numerically-generated near field data to perturb an admittance matrix rendered inaccurate through a deliberate undersampling of the conesphere geometry. Finally, results are given for the MoM network model algorithm with measured near field data, with the resulting predictions compared to measured far field truth. Algorithm performance is examined as a function of frequency for monostatic near field input data.
The image-based near-field to far-field transformation is based on a reflectivity approximation that is commonly used in ISAR imaging. It is a limited but computationally efficient transform whose accuracy, for appropriate targets, rivals that of computationally more intense transforms. Previous results include applications of the transform to lOA. long wire and lOA. long conesphere numerical data. Here, 1-D and 2-D versions of the transform are applied to conesphere near-field measurements data and the results are compared to corresponding far-field measurements data. Transform errors obtained for these data are compared to corresponding results obtained using newly generated near-field and far-field numerical data. The image-based transform is believed to be especially applicable to the far-field correction of near-field measurements of complicated targets like aircraft or vehicles that are too large or too poorly defined to be simulated numerically.
Image Editing and Reconstruction (IER) is used to estimate the RCS of component parts of a complex target. We discuss the general areas of controversy that surround the technique, and present a set of practical data processing procedures for assisting in validation of the process. First, we illustrate a simple technique for validating the end-to-end signal processing chain. Second, we present a procedure that compares the original unedited, but fully calibrated, RCS data with the summation of all IER components. For example, if we segregate the image into two components - component of interest, remainder of the target mounting structure plus other clutter - we require that the two patterns coherently sum to the original. This indirectly references the results to the calibration device. In addition, it provides a quantitative means of assessing the relative contribution of the component parts to overall RCS. We demonstrate the procedures using simulated and actual data.
Recently, a new method of wide band radar imaging has been developped within the framework of the two dimensional (2-D) continuous wavelet theory. Based on a model of localized colored and non isotropic reflectors, this method allows to obtain simultaneously information about the location, the frequency and the directi vity of the scatterers which contribute to the RCS of a target. We obtain a 4-D data set that we call hyperimage namely a series of images which depend on the frequency and orientation of illumination. In order to exploit efficiently hyperimages an interactive visual display software called i4D has been specifically designed. The purpose of this paper is to present the capabilities of i4D through the analysis of hyperimages constructed from monostatic and bistatic scattering data. The results show that the interactive and dynamic analysis that i4D procures allow to better understand the mechanisms that contribute to the RCS of targets.
A technology for target identification has been developed that is directly applicable to the analysis of the backscattering behavior of targets. For the latter purpose the target is placed on a turntable, and amplitude/phase data are collected over the aspect angle sector of interest, using a radar with sufficient bandwidth to resolve the target in range. For ground vehicles and small aircraft a range resolution of about 1 ft is sufficient. Standard processing is used to form an ISAR image over the appropriate aspect angle sector. The difference relative to the more conventional procedures is that the complex ISAR image, intensity and phase, is analyzed rather than only the intensity. This allows us to identify spurious responses that are generated by certain features on the target, but appear in locations other than those of the features. The analysis of the complex image permits us to associate the genuine image responses with the features responsible for the responses, so that the strength and type of backscattering can be determined for the target features. With respect to the type of backscattering, we can determine whether the effective location of the feature is stable, or whether it drifts with aspect angle or frequency. We. can also determine the effective crossrange and range widths of the various features. The features that can be analyzed are those with responses sufficiently strong to exceed the general background. This is typically a fairly large number.
Nearfield Systems Incorporated (NSI) provides antenna measurement systems to domestic and foreign, commercial and government customers with sophisticated requirements that demand custom solutions for RF, mechanical, thermal or software applications. NSI is continuously adapting existing designs to seek cost effective solutions for each customer's demanding specification. This paper discusses numerous near-field scanner designs to meet a variety of applications. Presented are designs for several vertical planar scanners, horizontal scanners, tilted planar scanners, and special scanners designed to attach to structures to test antennas in-situ.
Far-field range testing has been the standard at the Southwest China Research Institute of Electronic Equipment (SWIEE) and at other facilities in mainland China. SWIEE has recently commissioned a new spherical near-field measurement system from Nearfield Systems Inc. (NSI) and Hewlett Packard (HP) to improve its antenna measurement capability. The near-field system provides significant advantages over the older far-field testing including elimination of weather problems with outdoor range testing, complete characterization of the antenna, and improved accuracy. This paper will discuss the antenna types at SWIEE tested with the NSl/HP near-field system, and the results being achieved.
A large horizontal near field measurement facility has been validated and commissioned at Lockheed Martin's Sunnyvale, CA facility. The new measurement facility will be used for characterizing antennas for a variety of satellites over a frequency range of 1 26.5 GHz. A horizontal near field scanner with a 14m x 7.8m (46' x 26') effective scan area has been designed to allow for 9.8m (32') of vertical clearance permitting zenith oriented satellites to be easily positioned within the range and tested in an efficient manner. The facility will soon support the measurement of antennas that are in a vertical orientation. This is accomplished with a novel add-on that allows vertical planar near field scanning on the same range. The vertical scanner has an effective coverage area of 13.6m (45') horizontal x 9m (30') vertical. The system is being used to test commercial communications satellites.
The Plume Measurement Facility is a new outdoor facility providing the capability to characterize tactical rocket motor plumes. Radar cross section of the plume is measured by both a near field and a far field radar. Infrared/ultraviolet/visible (IR/UVNIS) charac teristics are measured by numerous instruments recording spacial, temporal, and spectral data. All instrumentation is calibrated and adjusted to realtime standard day meteorological data and all data is recorded on a common synchronized time base.
Antenna designs continue to evolve and change as the telecommunications market expands, and current trends are towards more complex and higher performance antennas. In particular active transmit/receive (T/R) modules have enabled manufacturers to build antennas with multiple beams and significantly improved performance. These antennas present challenges for performance verification and testing not previously encountered in continuous wave (CW) antenna measurements. For example, testing in a pulsed operating mode, multiple beam state testing and testing in high power transmit and low power receive modes. This paper examines pulsed antenna measurements and considerations for the range design. An instrumentation configuration is presented for a pulsed far-field antenna range.
Probe arrays based on the Advanced Modulated Scattering Technique (A-MST) permit rapid measurements of electromagnetic fields at microwave and millimeter wave frequencies. Applications of A MST probe arrays to diagnostic testing of a) large anechoic chamber environments and b) microwave antennas are summarized in this paper.
This paper presents the implementation of the time domain measurement technique in IRCTR's antenna measurement facility. Using electromagnetic pulses with duration and rise times in the order of 50 ps, the antenna characteristics are determined. From the pulse response, the behavior of the antenna is characterized in the frequency range 1-18 GHz. An X-band Standard Gain Horn (SGH) has been used to verify the overall performance of the measurement system. An excellent agreement between time domain and standard frequency domain measurements has been observed. This novel antenna measurement technique offers advantages over the traditional techniques for wideband measurements in frequency domain in reducing the measurement time and has great potentials. The paper describes the Antenna Time Domain Measurement (ATDM) system, including measurement results and summarizes the basic principles, error sources, advantages and disadvantages of such a measurement technique.