AMTA Paper Archive

This system provides improved techniques for controlling positioning axes, and secure transmission of position data from remotely located control systems. Advancements in controls technology have allows more complex configurations for use in the manipulation of RCS targets in indoor ranges. This paper will discuss a unique system design that provides automated testing and positioning of RCS test bodies. The current system uses seven axes of motion, and allows for simultaneous motion as well as synchronous motion of any axis pairs in the system. These axes include Target azimuth and elevation, Pylon azimuth and elevation, Upper and Lower turntable azimuth, and carriage linear drives. In addition, the concepts of secure data transmission through the use of specialized fiber optics are addressed. Finally, a complex set of safety interlocks and man and machine protection is discussed. The entire system is currently implemented and running in the Boeing range.

The Hughes Aircraft Company recently completed the design, development, and construction of a new engineering facility that is dedicated to providing state-of-the-art Radar Cross Section Measurements. The facility is located at the Radar Systems Group in El Segundo, California and consists of two secure, tempest shielded anechoic chambers, a secure high bay work area, two large secure storage vaults, a secure tempest computer facility, a secure conference room, and the normal building support facilities. This RCS measurement test facility is the result of Hughes committing the time and money to study the problems which influence user friendly RCS measurement facility design decisions. Both anechoic chambers contain compact ranges and RCS measurement data collection systems. A description of the facility layout, instrumentation, target handling capability, and target access is presented.

There are two main parts to an antenna or RCS measurement system: the measurement instrumentation, and the measurement environment or “range”. Performance of the measurement system is dependent upon both the instrumentation and the range. Developing a successful measurement system requires understanding both parts of the system. This paper describes a Compact Test Range that has been designed and built for the purpose of demonstrating antenna and RCS measurement performance of a complete measurement system. Additionally the Compact Test Range will serve as a development platform for future antenna and RCS products and systems. The purpose of the chamber, design objectives, design techniques, expected and measured performance are all discussed.

Lockheed’s Advanced Development Company (LADC), located in Burbank, California, has recently completed construction of a state-of-the-art indoor Antenna/RCS test facility. This facility is housed in a dedicated 40,000 square foot building which is a maximum of 80 feet high. This building contains three anechoic chambers providing Antenna/RCS measurement capability from 100 Mhz to 100 Ghz. The largest chamber, with dimensions of 64 feet by 64 feet by 97 feet is configured as a compact range. This chamber utilizes the largest collimating reflector that Scientific-Atlanta has ever constructed. Primary test usage of this chamber is for RCS measurements in the frequency band of 700 Mhz to 100 Ghz. The second chamber is configured as a tapered horn test range. Its dimensions are 155 feet long with a 50 foot by 50 foot by 55 foot volume measurement zone. This chamber is utilized for RCS tests in the VHF, UHF, and L frequency bands and antenna tests from 100 MHz and up. The third chamber, with dimensions 14 foot by 14 foot by 56 foot, is a far field chamber designed to check out and evaluate small items up to 100 GHz. The entire facility has been designed to maximize efficiency, minimize the cost of operation, and produce outstanding quality data from Antenna/RCS measurements. A number of innovative techniques in model handling, model access, and model security were incorporated into the facility design. These features, as well as utilization of unique Lockheed designed and built pylons, allowed achievement of all these goals.

Among its different facilities, C.E.A. has an indoor range for radar cross section (RCS) measurements over a wide frequency range from 0,1 GHz to 18 GHz. The dimensions of this anechoic chamber, 45m x 13m x 12m and a quiet zone diameter of about 3m, make it one of the largest in Europe. It consists in a parabolic reflector for frequencies higher than 0,8 GHz and a system using inverse synthetic aperture radar (ISAR) techniques for lower frequencies associated with a short pulse coherent radar instrumentation equipment. In addition to performant instrumentation and illumination systems, the main features of this installation dedicated to measure stealth objects, are low residual clutter, discrete target supports, and powerful processing software. The technical solutions adopted are described.

An HP 8510B based RCS measurement system is presented. It can be operated in CW, hardware gating, and fast-CW modes. A VAX-3800 computer and a MAP 4000 array processor are used to speed up the data analysis and a PS 390 graphic system is used to display graphic. Three ISAR techniques, i.e., DFT approximation, focusing image processing, and diffraction limited methods, are available in the analysis program to get the target image. With an amplitude taper removing technique, this system can measure large target whose size is almost up to the size of compact range reflector.

General guidelines for using software gating are presented. Examples which demonstrate both proper and improper use of gating are presented. The effects of RAM materials on the time domain signature and the selection of the gate parameters are discussed. A brief review of the general theory of high resolution RCS measurements is presented.

The new HP 8530A microwave receiver has been designed specifically for antenna and radar cross section (RCS) measurement applications. With its capabilities and features, high-speed single parameter and multiple parameter measurements are possible. High-Speed measurements are a necessity for certain applications but oftentimes other factors will determine the actual test time. Measurement speed for various applications will be discussed and, more specifically, multiple parameter measurements using the HP 8530A’s internal multiplexer or external PIN switching.

The frequency accuracy of the HP 8530A receiver and HP 8360 Series synthesizers in ramp sweep is measured using a delay line discriminator. The effect of the frequency error on measurement accuracy is derived for radar cross section (RCS) measurements of one and two point constant-amplitude, scatterers and for background subtraction. The results of swept and synthesized frequency measurements are compared, showing that the errors due to ramp sweep are negligibly small for practical RCS measurements.

This paper describes the target handling system that was developed for use in the compact range facility at the University of Pretoria. The system was locally designed and manufactured and comprises of a lift platform, RCS pylon and utility trolley. The pylon utilises a unique design approach resulting in a structure with very high stiffness and surface finish.

This paper describes the technique and advancement of diagnostic radar imaging technology by comparing past SAR and ISAR techniques to the more recent advancement of Autofocus SAR techniques. This recent advancement has meant the relaxation of the stringent mechanical stability requirements needed to produce high quality, high dynamic range, calibrated RCS images.

This paper will show that it is possible to make bistatic measurements in a compact range environments using near field scanning. A test scanner is designed and operated. Criteria for the accuracy of positioning and repositioning are presented. Algorithms for the transformation of the raw data into bistatic far field calibrated RCS are presented. Examples will be presented where comparisons with theoretical bistatic sphere data are shown. Bistatc pedestal interaction terms will be demonstrated.

Radar Cross Section (RCS) measurements are typically made at linear polarizations (usually horizontal and vertical) and the transmit and receive polarizations are the same (co-polarized). In addition, however, it is sometimes desirable to measure the cross-polarized RCS of a target (i.e., transmit horizontal, receive vertical or vice-versa). A complete set of both co-and cross-polarized RCS of a target is called a scattering matrix. This paper describes the algorithm used for calibrating a scattering matrix measurement in the McDonnell Douglas Technologies Inc. (MDTI), Radar Measurement Center (RMC). Verification data collected at Ka band on various targets is included to validate the algorithm and implementing computer code.

The radar cross section (RCS) of a target depends on nature environment as well as many physical variables. The objective of a compact range is to exclude environmental effects on RCS measurements of a target. It is also true for time gated RCS measurements as well. RCS obtained in above manners is more suitable for a space borne than for a ground based target. The contribution from surrounding environment is an inseparable part of RCS for a ship, truck, bridge, and building. We need a suitable method to characterize RCS of a ground based target and its dependence on the environment. The uncontrollable natural change makes environmentally dependent RCS results difficult to compare for a ground based target measured at different time instants. A way to reduce the uncertainties induced from changes is to exhaust all possible RCS measurements before the change. A measurement of this kind is referred to as a concurrent RCS measurement, which in a sense is equivalent to take an optical picture of a rapidly changing object with a strobe light. The step frequency radar located at Chesapeake Bay Detachment of Naval Research Laboratory is such a radar, which is equivalent to at least 45 single frequency radars operating simultaneously from 2.0-18.0 Ghz. Last year, we briefly mentioned this radar in our presentation. We will make a detail discussion of this radar and its capability on concurrent RCS measurements.

This paper compare some of the features and capabilities of gated CW and pulse radars for RCS and imaging measurements. At the conceptual level, these two types of radars are very similar. The primary conceptual difference is that a pulse radar has a relatively high bandwidth receiver while a gated CW system has a relatively narrow bandwidth receiver. The measures of performance of an RCS and imaging system include sensitivity, measurement time, clutter rejection, dynamic range and accuracy. Other considerations such as inter-pulse modulation may be important in some cases. For some applications, typically where long ranges are involved, a pulse system has significant performance advantages. For many applications, the performance advantage of a pulse system is not significant, particularly when viewed in light of the large difference in cost. This is particularly true of Quality Assurance applications which are normally characterized by both short range and lower budgets. Typically, the price of a gated CW system is in the range of ¼ to ½ the price of a comparable pulse system. This paper discusses general similarities and differences in the fundamental operating characteristics of the two systems. Specific performance measures are discussed including system sensitivity, gate performance, clutter rejection, and measurement times. Other considerations such as pulse modulation are discussed. A summary of the various considerations is presented in order to give the reader an understanding of the applications for which a gated CW system is more appropriate.

A bistatic calibration technique for wide-band, full-polarimetric instrumentation radars is presented in this paper. First general bistatic measurement problems are discussed, as there are the coordinate systems, the definition of polarization and the bistatic scattering behavior of convenient calibration targets. In chapter two the new calibration approach is presented. The general mathematical and physical description of errors introduced in the bistatic system is based on the radiation transfer matrix. The calibration procedure is discussed for the application with a vector network analyzer based instrumentation radar. For verification purposes measurements were performed on several targets.

Computer codes for the computation of scattering are based on physical, mathematical, and numerical assumptions and approximations that impact the accuracy of the results in ways that are not obvious or quantifiable analytically. This paper stresses the usefulness of a concurrent measurement program to provide reliable RCS data for targets of special interest in establishing the range of validity of the various assumptions upon which a specific computer code is based. This in turn assists in developing “modelling guidelines” restricting the design of computer models for input to the code such that reasonable accurate results are likely to be obtained.

Two measurement systems for Radar Cross Section (RCS) measurements are described. One system employs propagation over a ground plane whereas the other system employs free space propagation in an anechoic chamber for target illumination. A comparison of measured data for different targets over a wide range of frequencies is presented. The measured data is also compared to RCS data computed using the Numerical Electromagnetics Code (NEC) computer program. The results may be useful for evaluating radar systems operating in the HF band of frequencies.

This paper considers the radar cross-section (RCS) simulation, measurement, and analysis of rotating structures found in today’s modern airframes. Addressed will be scattering characteristics from helicopter main and tail rotor systems; how these characteristics can be simulated, measured, and reduced to identify the individual scatterers withing the helicopter. The effect of radar system parameters on the scattered signal will also be discussed. Finally, actual RCS measurements from helicopters in flight wil be resented and analyzed using the above discussed techniques.

Recently, the theory and computer programs on the Periodic Moment Method (PMM) for scattering from both singly and doubly periodic arrays of lossy dielectric bodies have been developed. The purpose is to design microwave wedge and pyramid absorber for low reflectivity so that one can improve measurements and/or reduce the size of the anechoic chamber. With PMM, the reflection and transmission coefficients of periodically distributed bodies illuminated by a plane wave have been accurately calculated on the Cray Y-MP supercomputer at the Ohio Supercomputer Center. Through these studies, some wedge and pyramid absorber configurations have been designed, fabricated and tested in the OSU/ESL Anechoic Chamber. Very good agreement between calculations and measurements has been obtained. In the 1990 AMTA meeting, several wedge absorber designs and results for the TM case and normal incidence were presented. In this paper, the measured and calculated frequency responses of some experimental wedge designs, as well as an 8” and 18” commercial wedge and pyramid absorber panels will be reported for both TM and TE polarizations. Time domain responses will also be shown for both measurements and calculations.