AMTA Paper Archive
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Tracking and Classification of Vehicles and Humans Using a Ground Wave Radar
This paper presents results from a tracking and classification radar that is contained in a coffee-can sized cylinder that sits directly on the ground. The 50 mW radar operates in the 3.1 to 3.6 GHz band using horizontal polarization. The results from earlier radar propagation channel studies will be discussed, including propagation characteristics as a function of polarization and frequency band. The design for this radar that exploits the channel propagation characteristics will be described. Data from tracking of vehicles and humans will be presented. Examples of the range profiles of groups of humans and of moving vehicles will be shown. We will also show a test of the capability of such a system to track humans through building walls.
A New Gated-CW Radar Implementation
This paper describes the new ORBIT/FR StingRay Gated-CW radar implementation that provides both performance and speed improvements over those previously utilized and fielded in RCS measurement systems. The radar is implemented using one or multiple pulse modulators used to provide gating of the transmit and receive signals, in conjunction with the new class of Performance Network Analyzer recently introduced by Agilent Technologies. The radar features an order of magnitude improvement in speed over that previously offered using implementations with the Agilent 8510 or 8530 network analyzer/receiver. In addition, base sensitivity improvements are realized, and the radar is more flexible with user selection among many IF bandwidth settings now available. The physical profile of the radar is also improved, meaning that additional performance gains may be realized by creating a more efficient packaging scheme where the radar may be located closer to the radar antennas, either in a direct illumination configuration or in a compact range implementation. These factors, when considered in aggregate, result in the new ORBIT/FR StingRay Gated-CW radar offering that provides a higher performance-to-cost value trade-off than was previously available to the RCS measurement community.
Reduction of Vertical Field Taper at a Ground-Bounce RCS Range
We have investigated a method that reduces the vertical field taper at a ground-bounce radar crosssection range using a vertical antenna array. An experiment was designed were the coherent data from two measurement channels were independently recorded and stored for post processing. The two datasets were weighted and added in the postprocessing to form the extended zone with improved vertical field taper. Vertically distributed point scatterers on a special test object were used to aid in optimizing the method using imaging techniques. The method is evaluated using simulations and measurements. The usefulness of this method for RCS measurements of full-scale objects such as vehicles and aircraft is discussed. We find that the method can be used to reduce the vertical field taper over a wide frequency band in the way that theory predicts.
An Approach to the Evaluation of Uncertainties for Complex RCS Measurement Data
The Radar Cross Section (RCS) measurement facility operated by the Stealth Materials Department of BAE SYSTEMS Advanced Technology Centre in the UK is an invaluable tool for the development of low observable (LO) materials and designs. Specifically, it permits the effect of signature control measures, when applied to a design, to be demonstrated empirically in terms of the impact on the RCS. The facility is operated within a 3m by 3m by 12m anechoic chamber where pseudo-monostatic, co-polar, stepped frequency data for a target can be collected in a single measurement run over a frequency range of 2- 18GHz, and for a range of azimuth and elevation angles using a Vector Network Analyser (VNA). The data recorded consists of the complex voltage reflection coefficients (VRC) for the chosen range of aspect angles. This includes data for the target, mount, calibration object, and the associated calibration object mounting where significant. All data processing is conducted offline using a bespoke post processing software routine which implements software time domain gating of the raw data transformed into the time domain prior to calibration. The significant sources of type A (random) and B (systematic) uncertainties for the range are identified, grouped, and an approach to the determination of an uncertainty budget for the complex S21 data is presented. The method is based upon the UKAS M3003 guidelines for the treatment of uncertainties that may be expressed by the use of real, rather than complex numbers. However, a method of assessment of the uncertainties in both real and imaginary parts of the complex data is presented. Finally, the uncertainties estimated for the raw VRC data collected are propagated through the calibration and the uncertainty associated with the complex RCS of a simple target is presented.
Analysis of Range Ambiguity Effects in a Gated Linear FM Homodyne Receiver
Radar systems that use pulsed waveforms for detection can be adversely affected by target returns whose round-trip time of flight is longer than the radar’s interpulse period. Unless techniques such as pulse repetition frequency (PRF) jitter or pulse phase encoding are employed, the receiver has no way of determining whether a target’s range is accurate. If this radar system is being used to collect radar cross section (RCS) data, the range ambiguities may exhibit themselves as clutter and cause unacceptable levels of data contamination. A Gated Linear FM Homodyne (gated LFMH) radar modulates its transmitted signal during the time of an individual chirp, or frequency sweep, which leads to two distinct PRFs; the chirp PRF and the interchirp pulse PRF. The chirp PRF is typically very low, on the order of tens to hundreds of chirps per second, and therefore insignificant with respect to range ambiguities. It is the interchirp pulse PRF that is typically of sufficient rate to factor significantly in the processing of data collected with range ambiguities present. This paper provides analysis of the effects of range ambiguities in a typical gated LFMH radar that occur during wideband RCS data collections. In addition, a method for optimizing the radar system parameters through the prediction of the range ambiguities will be shown.
ARKEN, A Measurement System for Dynamic Full-Scale RCS Measurements and ECM Evaluations in Operational Environments
To determine the radar cross section of full-scale objects in their operational environment, and for doing countermeasure evaluations, a radar measurement system has been developed. The system is mobile and flexible and can hence be placed in different surroundings. Its main objective is to make trustworthy and accurate measurements of the RCS of ground-, seaand air targets. This is achieved by a calibration procedure that is performed in connection to all measurements. The measurement system is well suited for RCS measurements in dynamic scenarios. The system can transmit radar signals that resemble the signals of existing threat systems. This property together with the fact that the system at the same time measures both the RCS of the target and the effects of ECM make the system well suited for ECM evaluation. Measurements have been made of many different types of targets on land, at sea and in the air. Different types of ECM, e.g. chaff, has also been evaluated.
Use of a Low-Cost Compact Measurement System for the Characterisation of Backscattering from Ship Superstructure Details
In this paper, the use of a low cost compact RCS measurement system is described, aimed at the characterisation of superstructure details. This system has been installed in a large room available within a shipyard, so that the measurement process is quite simple and efficient, even though under near-field conditions. Results are relevant to radar images and RCS, and can be used for the selection of details, for the optimisation of their backscattering and/or their installation process, and for the improvement of simulation codes. Comparison with simulations is also reported.
Thermal Sensitivity of a Compact Range
The ability to perform radar cross section (RCS) measurements, where background subtraction is applied, requires a measurement system that is very stable throughout the measurement time span. Background subtraction allows the measurement of low RCS components mounted in high RCS test bodies by permitting the scattering from the test body to be removed by coherently subtracting the test body (background) RCS from the target RCS measurement. Amplitude and phase variation of the illumination signal between the time that the target and background measurements are performed will limit the quality of subtraction achievable. Modern instrumentation radars can maintain extraordinary stability when exposed to controlled temperature environments, but controlling the temperature of a large compact range can be difficult. Other components of the measurement system, such as the reflector, can also be influenced by temperature fluctuations. Methods of controlling the thermal environment can have significant consequences. Lessons learned in the Advanced Compact Range at the Air Force Research Laboratory will be described.
Test and Assessment of a Direction Finding Antenna Measured on the Nose of an MH-47A Helicopter
One basic Direction Finding (DF) technique for Radar is Amplitude Based Comparison DF. Multiple directional antennas are placed around an aircraft to get a 360 deg view of the area. By placing these antennas on the aircraft, the antennas are subjected to reflections from the aircraft, which distorts the antenna characteristics. This antenna distortion causes errors in the measurement of the angle of arrival. The work presented here describes the measurement of the antenna characteristics of a cavity backed spiral antenna both by itself and attached to the nose of an MH- 47A helicopter nose measured in an anechoic chamber. The spiral antenna’s pattern was changed when it was measured on the helicopter. The effect this change in pattern has on the DF accuracy is discussed.
A Reflectometer for Antenna Measurements
The reflection coefficient of an antenna impacts the power transmitted by the antenna. Accurate characterization of this parameter is important in a communication or radar system. This paper discusses an implementation whereby a reflectometer is located near the antenna under test in an antenna range albeit far from the receiver. By placing the reflectometer near the antenna, the measurement uncertainty intrinsic to long cable runs can be minimized.
Multi-Purpose RCS/Antenna Test Facility at Nurad Technologies, Inc.
Antennas that are used aboard next generation airborne, maritime and ground vehicles are increasingly required to satisfy both conventional radiation pattern and gain requirements as well as new radar cross section (RCS) requirements. In response to these requirements, Nurad and ORBIT/FR recently completed design, installation, and verification of a high performance, multi-purpose antenna and RCS measurement facility at the Nurad site in Baltimore, Maryland. This compact range facility features a 60x36x26 foot shielded anechoic chamber and a precision machined, serrated edge, offset-fed reflector system that produces a 5.3’H x 8’W x 8’L quiet zone over the 2-50 GHz frequency range. The facility includes a unique feed room structure that positions the primary radar components close to the feed mount for RCS measurements, and allows for easy change of compact range feed antennas. A removable pylon assembly is used for test body support during RCS testing, and a unique add on section to the pylon rotator allows for inclusion of a roll axis that enables measurement of small and medium size antenna assemblies without removing the pylon. Measurements performed on low RCS standard targets and antennas made in the chamber demonstrate that the chamber provides a high performance measurement environment while providing ease of use and rapid configuration and target changeover.
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.
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