Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
In the last few years, the interest in millimeter wave systems, like radars, seekers and radiometers has increased rapidly. Though the size of narrow-beamwidth antennas in the 60-200 GHz range is limited to some 20 inches, an accurate far-field antenna test range would need to be very long. The achievement of precision antenna pattern measurements with a 70' or even longer transmission length requires the use of some power that is hardly available and expensive. A cost-effective and more accurate solution is to use a lab-sized compact range that presents several advantages over the classical so-called far-field anechoic chamber: - Small anechoic enclosure (2.5 x 1.2 x 1.2 meters) meaning low cost structure and very low investissement in absorbing material. No special air-conditioning is needed. This enclosure can be installed in the antenna laboratory or office. Due to the small size of the test range and antennas under test, installation, handling and operation are very easy. For spaceborne applications, where clean environment is requested, a small chamber is easier to keep free of dust than a large one. - The compact range is of the single, front fed, paraboloid reflector type, with serrated edges. The size and shape of the reflector and serrations have been determined by scaling a large compact range of ESD design, with several units of different size in operation. The focal length of 0.8 meter only accounts in the transmission path losses and the standard very low power millimeterwave signal generators are usable to perform precision measurements. The largest dimension of the reflector is 1 meter and this small size allows the use of an accurate machining process, leading to a very high surface accuracy at a reasonable cost. The aluminum alloy foundry used for the reflector is highly temperature stable. - Feeds are standard products, available from several millimeter wave components manufacturers. They are corrugated horns, with low sidelobes, constant and broad beamwidth over the full waveguide band and symmetrical patterns in E and H planes. - The compact range reflector, feeds and test positioner are installed on a single granite slab for mechanical and thermal stability, to avoid defocusing of the compact range. - A micro-positioner or a precision X Y phase probe can be installed at the center of the quiet zone. Due to their small size, these devices can be very accurate and stable. Due to the compactness of this test range, all the test instrumentation can be installed under the rigid floor of the enclosure and the length of the lossy RF (waveguide) connections never exceeds 1 meter.
This paper discusses the configuration and performance of millimeter-wave measurement systems comprised of standard Harris Shaped Compact Ranges, Hewlett Packard (HP) 8510B Network Analyzer, and Millitech frequency extenders designed for use with the network analyzer. Millimeter-wave capabilities have been integrated into the Harris automated measurement system to allow computer controlled millimeter-wave compact range characterizations. This system offers a new measurement alternative for antenna and Radar Cross Section (RCS) measurements. Measured 35 GHz data from the Harris Model 1606 compact range, and 95 GHz data from the Model 1603 compact range are included.
This paper describes methodology for performing high resolution target radar cross section (RCS) diagnostic measurements with a new type of portable multifrequency radar. The Model 200 radar system is capable of operating at extremely short ranges, and does not require an anechoic chamber for performing highly sensitive radar cross section measurements. Measurements can be made in conventional low range resolution polar plot modes, in high-range-resolution (HRR) mode, in Inverse Synthetic Aperture (ISAR) mode, and in Synthetic Aperture (SAR) mode. The radar is described and the implications for present and future measurement technology are discussed.
In the past, most radar-cross-section imaging has been done after data has been taken. At best, this off-line processing generates images that are returned to a customer the next day. Many projects can benefit significantly by having concurrent imaging and data acquisition. This allows for real-time cause and effect type diagnostics without rescheduling range time. As RCS range time becomes increasingly more expensive and difficult to schedule, real-time imaging provides the project engineer with a valuable tool to optimally use his range time. A technique has been developed to render real-time radar cross section images while acquiring data. All image processing is performed to achieve a fully enhanced image. Focussing, interpolation, and windowing are all used to give a detailed image. The system uses a Hewlett Packard 8510B for data taking and Hewlett Packard computers for data acquisition and image processing.
RCS instrumentation systems capable of combining wide-band and ISAR techniques to obtain two-dimensional images are widely used to perform RCS diagnostic and measurement functions. Objects involving rotating structures, such as blades of propulsion systems complicate the diagnostic task. The paper address the utilization of diagnostic RCS systems to meaningfully determine the radar signatures of objects with rotating components and presents results obtained from a generic data set, typically available from wide-band RCS instrumentation systems. The results provide valuable insight to the signature of objects with rotating components.
Signal processing techniques may be used in radar signature analysis to obtain radar target impulse response. In general there is a one to one relationship between specific scattering mechanisms and the time such mechanisms appear in the impulse response. One of the difficulties of this type of analysis is that complex targets often have multiple interactions. Many of these multiple interaction mechanisms can be identified as such by the application of the bispectrum to the radar scattering data. Also, the bispectrum forms a basis for discriminating between targets. Classification of unknown radar targets based on their bispectral response is performed in this study.
This paper examines the primary differences between gated-c.w. and pulsed-i.f. instrumentation radar systems. Following a brief explanation of the fundamental theory behind each radar type, a performance trade study is presented. The impact of i.f. bandwidth on the operation and performance of the radar is presented by first briefly describing the major similarities and differences between the two radar types and the resulting impacts on performance. Differences in the gate performance, sensitivity, dynamic range, speed, and accuracy are summarized. To show the performance advantages and shortfalls of each radar type, benchmark test scenarios are presented. The resulting summary can be used as a guide in determining the optimal radar type for a specific range geometry and measurement requirement.
Precise and complete measurements of advanced electromagnetic systems demand dramatically higher data acquisition speeds than those commonly attainable. Specific challenges include requirements for wideband measurements with arbitrarily spaced frequency steps. These types of measurements are often encountered in characterizing EW/ECM systems, radars, communications systems, and in performing antenna and RCS measurements. The Scientific-Atlanta Model 1795 Microwave Receiver offers capabilities directly applicable to solving measurement problems posed by highly frequency agile systems. These problems include: 1) timing constraints 2) data throughput 3) RF interfacing 4) maintaining high accuracy A technique is discussed which shows the application of the Model 1795 Microwave Receiver in its high frequency agility mode of operation. Measurement examples are presented showing the advantages gained compared to previous methods and instrumentation configurations.
The MUSIC (Multiple Signal Characterization) algorithm uses an eigenvector decomposition of measured data to classify signals in the presence of noise. It has been used for the angular classification of multiple radar signal emitters and ISAR imaging. Interest has grown in stray signal analysis in anechoic chambers. This paper will discuss the modification and use of the MUSIC algorithm for the decomposition of field probe data to angular spectrum. A brief discussion of the MUSIC algorithm theory will be presented. Modifications required for use in compact range angular spectrum analysis will be discussed in detail. Requirements on field probe measurements will be presented as well as their effects on the implementation of the algorithm. Both one way and two way measurements are considered for their relationship to the array manifold. Finally, some experimental validation generated on the Boeing range will be presented.
In this paper the initial construction and validation phase for a new elevated outdoor antenna range is described. The facility is designed to provide excellent pattern, gain and reflection measurements in the 20 MHz to 40 GHz frequency range for apertures and arrays up to D = 16 feet in length. Shown in detail is a physical description of the facility and equipment, an error budget and the results of field probing and antenna measurements. A discussion of the results shows a facility capable of antenna measurements at S/N levels of 60 dB providing a dynamic range of over 40 dB with error levels less than plus-or-minus 0.44 dB. Throughout the discussion, special attention is given to the full automation of the range in Phase 2 and its possible use for radar cross section measurements.
The Vulnerability Assessment Laboratory (VAL) anechoic chamber at White Sands Missile Range, New Mexico was reconfigured and refurbished during the last part of 1988. This paper will be a facility description of the state-of-the-art Special Electromagnetic Interference (SEMI) investigation facility. Electromagnetic susceptibility and vulnerability investigations of US and, in some cases, foreign weapon systems are conducted by the EW experts in the Technology and Advanced Concepts (TAC) Division of VAL. EMI investigations have recently been completed on both the UH-50A BLACKHAWK and AH-64A Apache helicopters in the chamber. The paper will cover the facility's three anechoic chambers, shielded RF instrumentation bay, computer facilities for EM coupling analyses, and the myriad of antenna, antenna pattern measurement, amplifier, electronic, and support instrumentation equipment for the chambers. A radar cross section measurement and an off-line RCS data processing station are also included in the facility.
The purpose of this paper is to discuss the accuracy requirement of a generic measurement system for in-flight antenna pattern evaluations. Elements of the measurement technique will be described. An attempt is made to distinguish the measurement requirement for a narrow beam radar antenna in contrast to that for broad beam communication antennas. Major elements of the measurement technique discussed include the flight path geometry, the multipath propagation problem, and the measurement errors. Instrumentation requirements consist of the ground segment, the receive and the tracking subsystems, and the airborne equipment, the radar components and the navigation and attitude sensors. Considering the in-flight antenna pattern testing as a generalized antenna range measurement problem, various sources of measurement errors are identified. An error budget assumption is made on each error component to estimate the overall expected accuracy of the in-flight antenna pattern measurement.
Under many circumstances it is necessary to experimentally estimate the radar cross section of targets in a cluttered environment. A significant reduction in the clutter can be obtained when cross range filtering can be done. In this experimental RC measurement concept, scattering measurements are performed using a moving radar antenna. Thus scattering as a function of target plus clutter versus aspect angle in the near field can be measured. Next, a back projection algorithm can be used to estimate the scattering as a function of position in the neighborhood of the target. The known range to which the signal is to be focussed is used to project back to the target area. An estimate of the RCS at points along a line in the plane of the target is computed. The clutter responses can then be removed from the data, and the remaining target-only values projected forward again (possibly to the far field) to estimate the RCS of the target alone.
In the theory of inverse synthetic aperture imaging of radar targets the measuring distance is ordinarily supposed to be very much larger than the dimensions of the target. If this is not the case errors are introduced. We study these errors and means to decrease their influence by computation. The result is that the maximum tolerable target dimension can be substantially increased in a plane perpendicular to the axis of rotation if error correction is used.
The Synthetic Aperture Radar Antenna for the European Remote Sensing Satellite ERS-1 is a 10 by 1 metre deployable slotted waveguide array operating at 5.3 GHz. Electrical performance of the complete antenna is derived at the end of the environmental test programme from near field measurements on a planar NF scanner. In order to obtain very early information on electrical integrity of the flight model antenna, suitable for pre- and post-environmental comparison, a fast electrical functional test was implemented in the total test sequence. It basically consists of a 2D slot probing of a well distributed number of slots in combination with complex input impedance measurements. The paper describes the method and presents results of different test steps. The data of pre-/post-environmental measurements are compared.
In the past, models suspended indoors for radar cross-section measurements have weighed up to several hundred pounds, suspended on the order of 20' or less from the ground, and measured statically or rotated for great circle cuts. Under these circumstances it has been acceptable to choose the best string configuration from a signature point of view and simply wait for the model to reach a visually calm state before testing. However, indoor ranges are now requiring suspension of models weighing several thousand pounds 40' or more above the floor. In addition, the demand for imaging data during model conics requires both precise dynamic control and model stability. This work discusses techniques developed at Boeing's 9-77 Range in Seattle, to achieve model stability during suspension and manipulation. In addition, techniques to determine spring and damping constants of suspension systems for individual models are addressed.
Dielectric straps can support very heavy targets and have a low radar cross section (RCS), especially at low frequencies (below 8 GHz). In this paper, the scattered fields of dielectric straps surrounding a perfectly conducting structure are presented, and the computed results are compared with experimental data. Empirical formulas for the strap scattered fields are also given. These formulas are good for general convex structures and are expected to give a reasonable estimate of the true RCS of the dielectric straps when used as a target support structure.
A stressed-skin inflatable target support provides an improvement over a foam column for radar cross section (RCS) measurements in an anechoic chamber. Theoretical analysis indicates that backscatter from the support is minimized because its mass is reduced below that of a foam column and is distributed to favor incoherent scattering. Compared with a foam column, a pressurized thin shell has superior mechanical stability under both axial and transverse loads. Experimental observations using Mylar -- a low dielectric constant, high tensile strength film -- confirm these results. Spurious reflections from rotational machinery located below an inflatable column are reduced by a layer of absorber within the base of the inflatable support.
Many targets today exhibit radar cross sections sensitive to the angular orientation of the target. While some of these targets have prominent scattering centers which can be exploited to obtain a relative positional reference, many targets unfortunately do not. In addition, many complex targets have a highly directional scattering behavior requiring careful alignment to the incident planar field. This need for accurate positioning has prompted the development of laser alignment techniques for the compact range. One such system has been under development at the ElectroScience Laboratory, and the designs and results of the first prototype are presented here. Performance goals and design criteria are discussed, and future improvements are considered. In addition, similar systems for feed and pedestal location reference systems are presented.
The requirement to measure lower radar cross-section (RCS) levels within anechoic chambers has demonstrated the need to further analyze the performance of microwave absorbers. The interactions of the feed system, compact range reflector, target mount, and target/test body with the microwave absorber greatly effect both the measurement accuracy and ambient noise level within the anechoic chamber. Better absorber characterization and understanding leads to improved chamber performance analysis and chamber design modeling. Past absorber studies have evaluated the backscatter performance of most absorber types, however, bistatic performance characterizations have been limited. This paper will discuss a method of obtaining bistatic absorber data which offers the advantages of time gating and synthetic aperture imaging to improve measurement isolation and accuracy. The approach involves illuminating a large absorber test wall about several incidence angles with the plane wave generated by a compact range. A receive antenna is then moved about the test wall and bistatic scattering is observed. The technique provides improved measurement results over methods utilizing NRL arch type systems. Bistatic absorber data has been collected and analyzed over angles from normal to near grazing incidence. Test results will be demonstrated with different absorber shapes, sizes, orientations, and material transitions from wedge to pyramidal. Various bistatic conditions will be analyzed for both polarizations over a number of frequencies.