AMTA Paper Archive
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Effects of Positioning Errors on the Circular image-Based Near Field-to-Far Field RCS Transformation
In this paper, we present an analysis of the impact of positioning errors on the performance of the GDAIS circular image-based near field-to-far field RCS transformation (CNFFFT). The analysis is part of our continuing investigation into the application of near fieldto-far field transformations to ground-based signature diagnostics. In particular, the analysis focuses on the errors associated with ground-to-ground, near-field, whole-body measurements where the radar moves on a nominally circular path around the target. Two types of positioning errors are considered: slowly-varying, long term drift and rapidly-varying, random perturbations about the nominal circular path. The analyses are conducted using simulated data from a target comprised of an array of generalized point scatterers which model both single and multiple interactions on the target. The performance of the CNFFFT was evaluated in terms of the angle sector cumulative RCS statistics. The analyses were performed as a function of frequency for varying amounts of position error, both with and without (approximate) motion compensation. As expected, the results show that the CNFFFT is significantly more sensitive to rapidly-varying position errors, but that acceptable performance can be achieved with motion compensation provided an accurate estimate of the errors is available.
Time-Frequency Analysis of Time Varying Spectra with Application to Rotocraft Testing
The time-dependent spectrum of rotating structures presents many significant challenges to radar cross section (RCS) test design, instrumentation parameter selection, signal processing methodology, data analysis, and data interpretation. This paper presents a multi-dimensional signal processing tool and a suite of associated data products, based on an efficiently scripted test design and execution strategy, that are responsive to the high throughput, high data volume requirements and real time data analysis demands associated with rotorcraft testing. We specifically address the NRTF’s realization of a suite of spectral, cepstral and statistical signal processing tools supported by animation that facilitate near-real time parametric data analysis and interpretation.
RCS Time Domain Near Field measurement and 2D ISAR
This paper presents a Radar Crossed Section (RCS) time-domain near-field measurement and its Inverse Synthetic Aperture Radar (ISAR) imaging. The target includes a pyramidal horn and a metallic aircraft scale model. A pulse generator excites the transmit antenna and a digital sampling unit collects the data at the receiving side. A time gating window is subsequently applied to reject the multiple reflections. An efficient 3-D algorithm for ISAR based on time-domain near-field data is presented. The test results for six cases demonstrate excellent ISAR images. In particular the geometry of 3-D reconstructed target can be displayed in perspective manner. The advantage of using time-domain near-field measurements is three-fold. First, it reduces measurement time in the order of one-tenth compared to frequency-domain measurements. Second, it mitigates the multiple reflection effects via time gating. Third, near-field measurements require relatively little real estate which reduces the cost tremendously since a compact range is not needed.
A New Detection - Estimation Scheme for high Resolution Radar Cross Section Imaging
Radar cross section analysis essentially rely on classical spectral analysis methods. By inverse Fourier transforming the scattering coefficients, one can deduce the amplitudes and localizations of the scatterers. Unfortunately, such methods suffer from a lack of resolution since it is tied to the inverse of the extent of the data domain of interest. The use of high resolution spectral analysis can help to overcome these difficulties. Nevertheless, the expected gain of resolution is due to the enrichment of the model that is fit to the data (usually a sum of complex exponentials). One of the key point is then the order of the model, which can usually be found with appropriate criteria (MDL, AIC,…). The amplitudes and positions of the scatterers are finally estimated. The algorithm proposed here performs the detection and estimation tasks at the same time, which turns out to be more robust than conventional sequential algorithms.
Study of Calibration Targets of Full-polarimetric RF Measurement
Co-polarized and cross-polarized radar cross sections (RCS) are required to completely characterize a complex target. However, it is common for a RCS range to measure only the co-polarized RCS. This practice is primarily due to the inability to produce accurate cross-polarization analysis data for the calibration targets. The most commonly used calibration targets, spheres and cylinders, cannot be used to calibrate cross-polarized RCS due to lack of cross-polarized returns. In this paper, we consider objects that can potentially be used as calibration targets for cross-polarization measurements. Specifically, we numerically study the cross-polarized responses of the Tungsten rod, the grooved cylinder, and triangular dihedrals. Co-polarized measurement data are also included in this initial assessment. From this initial study, we find the counter-balanced dihedral to be a suitable calibration target for cross-polarized measurements.
Active Antenna Measurement System with High speed Time Synchronization
Phased arrays antennas are designed to control their radiation characteristics by accurately setting the phase and amplitude distribution of the elements. Inaccurate control of the phase and amplitude can significantly alter the radiation pattern of an array. In fact, the operating principle of scanning arrays of elements for applications such as target tracking or mobile satellite communications, where the requirements for low side lobes and high gain are of very high importance, is primarily based on precise control of the phase and amplitude of the elements. For these reasons, the complexity of antenna measurement system design for phased array antennas measurements involves high accuracy and precise time synchronization between all the components of the system. This paper presents a comprehensive solution for accurate and reliable measurement of very large phased array antennas at high frequencies. The presented solution addresses the following issues: • Accurate positioning of the RF sensor / probe. • High-speed multi – frequency data collection. • High-speed multi - port data collection. • Programmable and real-time TTL position event triggers. • Pulse measurement. • Multi beam measurement. • Synchronization with the radar computer.
Electromagnetic Material Characterization Using Partially Filled Rectangular Waveguide
A waveguide material measurement technique is developed for highly reflective or lossy materials. In order to extract the complex constitutive parameters from a material, experimental reflection and transmission scattering parameters are needed. In a traditional rectangular waveguide material measurement, the sample fills the entire waveguide cross-section, making it difficult to obtain a significant transmission scattering parameter with highly reflective or lossy materials. This paper demonstrates, through the use of a modal-analysis technique, how using a partially filled rectangular waveguide cross-section allows for better transmission responses to extract the complex constitutive parameters. Experimental results for acrylic and radar absorbing material are compared to stripline measurements to verify the modal-analysis technique.
An Automated Cylindrical Near-Field Measurement and Analysis System for Radome Characterization
The David Florida Laboratory (DFL) was contacted by the Canadian Department of National Defense (DND) to develop an accurate, reliable, more cost effective method of characterizing existing nose cone mounted radomes for the radar systems aboard aircraft such as CF-18. Traditionally, these measurements have been performed in a far-field (FF)  range using conventional positioning and measurement systems and specialized instruments such as a null seeker. Recently, the use of near field methods has been incorporated in radome measurement practices . This paper describes one such adaptation of a cylindrical near-field facility (CNF) for radome measurements.
A Unique Approach to Frequency-Modulated Continuous-Wave Radar Design
Frequency-Modulated Continuous-Wave (FMCW) Radar has traditionally been used in short range applications. Conventional FMCW radar requires the use of expensive microwave mixers and low noise amplifiers. A uniquely inexpensive solution was created, using inexpensive Gunn oscillator based microwave transceiver modules that consist of 3 diodes inside of a resonant cavity. However these transceiver modules have stability problems which cause them to be unsuitable for use in precise FMCW radar applications, when just one module is used. In order to overcome this problem, a unique radar solution was developed which uses a combination of 2 transceiver modules to create a precise FMCW radar system. This unique solution to FMCW radar is proven to be capable of determining range to target, and creating Synthetic Aperture Radar images.
Progress Report on the IEEE APS RCS Measurement Standard
This paper discusses the status of the RCS Measurement Standard, IEEE Standards Project P1502. This standard (actually a “recommended practice”) is sponsored by the Antenna Standards Committee of the IEEE Antennas and Propagation Society (Mike Francis, 2004 Chair). The title is “Recommended Practice for Radar Cross Section Test Procedures”. The standard is being generated by the Radar Cross Section Subcommittee of the IEEE AP-S Antenna Standards Society (Dr. Eric Walton, 2004 Chair). The RCS Measurement Practice Standard is being written for the personnel responsible for the operation of a test range, and not for the design of such a range. The purpose of this presentation is to give the community an update on our progress. The briefing will also review the contents and direction the document is heading. We solicit input from members of the community with a goal of getting the document released for general review within the IEEE and publication within the next year.
Rotorcraft Measurement Capability at the National RCS Test Facility
The National RCS Test Facility (NRTF) has measured radar cross section (RCS) of fixed wing aircraft for many years. In order to expand our testing options at the NRTF Mainsite test facility, the NRTF has developed a rotorcraft measurement capability. The design is compatible for use with our 50-foot pylon, but unlike existing rotators, allows for RCS measurement of test articles that require significant forward and aft target pitches. Target mounting and positioning was not the only challenge. Our new capability required the control and collection of rotor blade position information, in addition to the control and collection of traditional target azimuth and elevation data. Modification of our existing acquisition software and command and control systems was also required. In order to maintain the integrity of the NRTF’s calibration processes and enable the use of existing calibration devices, hardware was constructed to enable mounting of these devices to the spindle system. Other important considerations that influenced the design and implementation of the spindle mount capability include cost effective mounting/dismounting of test articles (to include the targets and calibration devices) safety of the test articles and personnel, and the effective determination of backgrounds.
Evaluation of an Ultra wide Bandwidth Phased Array Antenna for Indoor V/UHF RCS Measurements
CAMELIA is one of the three anechoïc chambers of the French Atomic Energy Center (CEA). It is equipped with a compact range reflector and a pulsed radar allowing antenna and RCS measurements from 800 MHz to 18 GHz. Below 800 MHz, measurements are made with different kind of antennas (log- periodic, horns, arrays…). Nevertheless, measurements at such low frequencies suffer from serious artifacts due to coupling effects. This paper describes a particular array we designed, realized and characterized to cover the 100 MHz – 2000 MHz bandwidth. Although the antenna diagram shape was the most constraining factor, the ability to cover the whole bandwidth with as few handling as possible was the major issue.
High Accuracy Horizontal Scanner Operating in X-band for the Measurement of a Spaceborne Synthetic Aperture Radar (SAR) Antenna
ELTA is now in the process of designing and building a new spaceborn SAR “TECSAR” – Israel Synthetic Aperture Radar (SAR) X-Band lightweight satellite. TECSAR contains an ultra-light weight high accuracy Paraboloid deployable reflector antenna. TECSAR’s electronic beam steering capability is achieved by using a feed array in the focal plane. For future testing at ELTA, Israel, an horizontal Planar near-field antenna test range (7m x 8m scan) has recently been completed by ORBIT/FR to allow testing of large fully integrated space antennas as stand alone as well as integrated with a satellite The paper will describe: o Short TECSAR SAR antenna description o The special requirements of the measurement system o System design and measured performance
Update on the Air Force Research Laboratory Advance Compact Range Calibration Uncertainty Analysis
A calibration uncertainty analysis was conducted for the Air Force Research Laboratory’s (AFRL) Advanced Compact Range (ACR) in 2000. This analysis was a key component of the Radar Cross Section (RCS) ISO-25 (ANSI-Z-540) Range Certification Demonstration Project. In this analysis many of the uncertainty components were argued to be small or negligible. These arguments were accepted as being reasonable based on engineering experience. Since 2000 the ACR radar has been replaced with an Aeroflex Lintek Elan radar system. A new measurement uncertainty analysis was conducted for the ACR using the Elan radar and for a general (non-calibration) target. We present results comparing the previous results to the current analysis results.
SOLANGE, An Enhanced RCS Measurement Facility of Full Size Aircraft
This paper describes the RCS measurement test facilities, CHEOPS, STRADI and SOLANGE which are operated in the Technical Center for Information Warfare (CELAR) in France, with a particular focus on SOLANGE. CHEOPS is an anechoïc chamber convenient for the measurement of small missiles as well as antennas measurement. STRADI is an outdoor facility, which is convenient for measurement of land vehicles, helicopters and large antennas. SOLANGE is an indoor RCS measurement facility used to measure long missiles and aircraft. Originally built in 1985, SOLANGE has been continuously upgraded to fulfill all customers requirements in the field of RCS measurement. Thanks to the in house radar instrumentation and data processing software, SOLANGE can reach a very good performance on small or big RCS targets from 200 MHz to 18 GHz. The UHF/VHF capacity has been recently enhanced thanks to the upgrade of the positioning system and the cooperation between CELAR and CEA.
Accurate Determination of a Compact Antenna Test Range Reference Axis and Plane Wave Quality
Highly accurate antenna and payload measurements in antenna test facilities require highly accurate alignment and boresight determination. The Angle of Arrival (AoA) of the plane wave field in the quiet zone of the CCR Compensated Compact Range CCR 75/60 of EADS Astrium GmbH, installed at Alcatel Space in Cannes . France, has been measured using three different methods (optical geometrical determination using theodolites, Radar Cross Section (RCS) maximization, planar scanner phase plane alignment). The proposed paper describes the three methods and the performed measurement campaign and provides the correlation between the resulting angles via a comparison of the results. The achieved absolute worst case values of lower than 0.005° demonstrates the high level of accuracy reached during the campaigns.
A Phase Hologram Based Compact RCS Range for Scale Models
A compact radar cross section (RCS) test range for scale model measurements is being developed. The test range is based on a phase hologram that converts the feed horn radiation to a plane wave needed for RCS determination. The measurements are performed at 310 GHz using continuous wave operation. A monostatic configuration is realized using a dielectric slab as a directional coupler. The main advantage of a scale model RCS range is that the dimensions of radar targets are scaled down in proportion to the wavelength. Therefore, RCS data of originally large objects can be measured indoors in a controlled environment. So far simple test objects such as metal spheres have been measured. The feasibility of the phase hologram RCS range has been verified. The basic operation and first measurement results of the monostatic measurement range are reported here.
Anechoic Chamber Quiet Zone Requirements for Mobile Handset Testing
Shielded anechoic chambers have been extensively used to measure antennas for various applications. Recent proliferation of mobile telecommunications presented high demands for measurements of antennas that are used in mobile wireless handsets. Since antennas in mobile handsets are low-directive for better mobile links to base stations, they are capable of transmitting or receiving nearly all unwanted reflected signals from imperfections through various reflection and scattering paths in the anechoic chamber in addition to desired signal from the direct path during the measurements. The Quiet Zone (QZ) characterization method has to be re-examined. This paper presents measurements and analyses comparing the difference in chamber designs and verifications of anechoic chamber QZ’s. Through this development, design guidelines are provided to improve the anechoic chamber QZ signal-to-noise ratio for measuring low-directive antennas. Techniques derived from this requirement can also benefit for measurements of high sensitivity Radar-Cross-Section.
Antenna Pattern Correction for Near Field-to-Far Field RCS Transformation of 1-D Linear SAR Measurements
In a previous AMTA paper , we presented a firstprinciples algorithm called wavenumber migration (WM) for estimating a target’s far-field RCS and/or far-field images from extreme near-field linear (1-D) or planar (2-D) SAR measurements, such as those collected for flight-line diagnostics of aircraft signatures. However, the algorithm assumes the radar antenna has a uniform, isotropic pattern on both transmit and receive. In this paper, we describe a modification to the (1-D) linear SAR WM algorithm that compensates for nonuniform antenna pattern effects. We also introduce two variants to the algorithm that eliminate certain computational steps and lead to more efficient implementations. The effectiveness of the pattern compensation is demonstrated for all three versions of the algorithm in both the RCS and the image domains using simulated data from arrays of simple point scatterers.
A Low-Cost Compact Measurement System for Diagnostic Imaging and RCS Estimation
The task of performing reliable RCS measurements in complex environments under near-field conditions is gaining more and more interest, mainly for a rapid assessment of RADAR performance of constructive details. This paper describes a low-cost compact measurement system fully developed by IDS, that allows fast and effective acquisition of diagnostic images under nearfield conditions and far-field RCS estimation in a nonanechoic environment. The hardware of the system is composed of a planar scanner, two horn antennas, a Vector Network Analyzer and a computer. The two axes scanner allows 2D scanning of antennas in a vertical plane. For each point of a predefined grid along the scanned area, the Analyzer performs a frequency scan. The acquisition software synchronizes scanner movements with data acquisition, transfer and storage on the computer’s HDD. The software has post-processing capabilities as well. A number of focusing algorithms permit to produce 2D and 3D diagnostic images of the target as well as 2D backprojection. It is moreover possible to reconstruct the RCS starting from near-field images. Along with system features, a summary of performances and some simple targets images are presented.
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