AMTA Paper Archive
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Hand-Held Portable Radar-Imaging Camcorder
A portable handheld antenna array system (SARBAR) capable of generating high-resolution two dimensional spotlight radar images is designed and built. The design goals were to build a portable device with maximum sensitivity, that can generate zonal images of a target at close range, and produce live updates of the scene (goal of 10 image per second). To achieve the design goals, an array antenna setting with separate transmit and receive elements have been used. The radar system is based on conventional FM-CW homodyne radar. The novelty of the design, however, is that for each FM CW waveform, the signal is successively routed through all the transmit elements and received from the designated receive elements. The transmit/ receive switching is such that a complete scan over the entire frequency and aspect interval is obtained in less than 80 msec. This allows image update rates that make the SARBAR resemble a video camcorder.
AFRL Advanced Compact Range RCS Uncertainty Analysis for a General Target
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. The scope of the RCS uncertainty analysis for the demonstration project was limited to calibration targets. Since that time we have initiated a detailed RCS uncertainty analysis for a more typical target measured in the ACR. A “more typical” target is one that is much larger with respect to wavelength than the calibration targets and characterized by a wide dynamic range of RCS scattering levels. We choose a 10’ ogive as the target due to the fact it is a large target, exhibits a wide dynamic range of scattering, and the scattering levels can be predicted using readily available CEM codes. We will present the methodology for the uncertainty analysis and detailed analyses of selected component uncertainties. The aspects of the uncertainty analysis that are unique to the “typical target” (i.e., a non calibration target) will be emphasized.
Outdoor Broadband RCS Measurements of Model Scale Aircraft
In real life, most radar targets are located outdoors. Here we present results from outdoor broadband RCS measurements at the X-, Ka- and W-band of “Holger”, a metallized model-scale aircraft with cavities. RCS vs. angle data in the wing plane (0° elevation) were recorded at discrete frequencies (9, 35 and 94 GHz) in both horizontal (HH) and vertical (VV) polarizations. ISAR data at 7-13, 32-38 and 92-97 GHz were acquired. Results from a 104.1 m ground range and a 162.7 m free space range will be compared.
Active Stability Control of Pulsed IF Radars
This paper presents the design and performance characteristics of a novel active stability control capability that Aeroflex Incorporated has developed and implemented in the élan-2000 pulsed-IF instrumentation radar. The real-time technique incorporates an internal power reference loop that continuously monitors and compensates for phase and amplitude drifts within the radar RF analog circuitry through high-speed processing of the streaming data collections. Vector corrections are applied to each recorded data point, using internal loop samples of the transmit pulse from a common RF channel and digitizer, without degrading other overall system performance capabilities. Demonstrated stability levels exceed –50 dB over the full operational RF bandwidth, for periods of several hours, with environmental temperature variations of several degrees. This measurement mode provides ~30 dB of improvement over conventional instrumentation radar systems under similar test conditions, which consequently enables significant improvements in measurement applications incorporating background subtraction or where extremely stable system parameters are required.
Portable Dechirp-On-Receive Radar
Sensor Concepts Inc. has prototyped a fast, lightweight, dechirp-on-receive radar called the SCI-Lr to provide the capability of a range instrumentation radar in a highly portable package. The small weight, size and power requirements of the SCI-Lr allow a variety of new deployment options for the user including in a small general aviation aircraft or on a mountaintop that is accessible only by four wheel drive. Pulse rates up to 20 KHz enables investigation of high Doppler bandwidth phenomenon such as ground vehicle microdoppler features. The dual integration from dechirp-on-receive matched filtering in fast time and Doppler processing in slow time provides high sensitivity with low output power. Planned enhancements of waveform bandwidth up to 2 GHz , frequency operation between .2 and 18 GHz and pulseto- pulse polarization switching will provide high information content for target discrimination. The flexibility provided by the hardware is augmented by software tools to examine data in near real time to monitor data quality and sufficiency. A variety of applications are being investigated including RCS measurement, SAR and ISAR imaging, Ground Moving Target Indication, and signature collection for ATC.
Spectral Response From Linear FM Radar
The true RF spectral response represents In- phase and Quadrature (I and Q) data in the frequency domain, and is identical to that mea- sured in many anechoic chambers including the one at Mission Research Corporation. Given a Linear FM (LFM) response, a method is derived that extracts the true RF spectral response. In the process some basic features of LFM systems are explained. The derivation depends on the assumption that the received signal is zero outside a de¯ned interval. Validation consists of applying the extraction process to both sim- ulated and measured LFM data from the ERIM DCS radar system.
The RCC/SMSG Certification of Lockheed Martin Orlando Florida
The Range Commanders Council Signature Measurement Standards Group (RCC/SMSG) Performed a Demonstration program with three DOD Radar Cross Section Ranges to evaluate and improve their documentation and evaluation process and criteria documented in what is known as a "Range Book". After a successful Demonstration Program, The RCC/SMSG has embarked on the evaluation of Industry RCS Range Calibration and measurement processes and procedures and compliance with the RCC/SMSG ANSI-Z540 (ISO-25) evaluation criteria. The Lockheed Martin Helendale RCS Range was evaluated by a committee of industry volunteers appointed by the RCC/SMSG after a review of their experience and credentials. The Lockheed Martin Orlando RCS Range requested an evaluation of their "Range Book" shortly after the completion of the Helendale evaluation. Each review committee is made up of three RCC/SMSG approved reviewers, at least one of which has participated in a previous review either as a review requester or a review committee member. This paper will put forth the process used by this review committee and the lessons learned from this and previous reviews. This paper will also discuss the RCC/SMSG process for obtaining an RCC/SMSG review.
Archimedean Spiral Antenna for Stepped Frequency Radar Footprint Measurements
This paper refers to a special type of antenna, called frequency independent antenna, used in Stepped Frequency Continuous Wave (SFCW) radar employed for humanitarian demining. The radar transmits 128 frequencies within the frequency range from 400 MHz to 4845 GHz, in groups of 8 simultaneously transmitted frequencies. It has been built at the International Research Center for Telecommunications transmission and Radar (IRCTR), Delft University of Technology. Two Archimedean spiral antennas with opposite sense of rotation, in order to decrease coupling signal below –55dB, have been chosen. Precise antenna behavior characterization is needed because SFCW radar is phase sensitive. The paper is focused on antenna footprint measurements, translating data from frequency domain to time domain and gating in order to remove any unwanted signals. Some phase and amplitude pattern using gating measurements are presented.
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.
Antenna Pattern Comparison Between and Outdoor Cylindrical Near-Field Test Facility and an Indoor Spherical Near-Field Antenna Test Facility
A new spherical near-field probe positioning device has been designed and constructed consisting of a large 5.0 meter fixed arc. This arc has been installed in a near-field test facility located at Alenia Marconi Systems on the Isle of Wight, UK. As part of the nearfield qualification, testing was performed on a ground based radar antenna. The resultant patterns were compared against measurements collected on the same antenna on a large outdoor cylindrical near-field test facility also located on the Isle of Wight . These measurements included multiple frequency measurements and multiple pattern comparisons. This paper summarizes the results obtained as part of the measurement program and includes discussions on the error budgets for the two ranges along with a discussion on the mutual error budget between the two ranges.
Far-Field Bistatic RCS From Near-Field Measurements
Bistatic radar cross sections of targets are computed from field measurements on a cylindrical scan surface placed in the near field of the target. The measurements are carried out in a radio anechoic chamber with an incident plane-wave field generated by a compact-range reflector. The accuracy of the computed target far field is significantly improved by applying asymptotic edge-correction techniques that compensate for the effect of truncation at the top and bottom edges of the scan cylinder. The measured field on the scan cylinder is a “total” near field that includes the incident field, the field of the support structure, and the scattered field of the target. The background subtraction method determines an approximation for the scattered near field on the scan cylinder from two measurements of total near fields. The far fields of metallic sphere and rod targets are computed from experimental near-field data and the results are verified with reference solutions.
Phase-Dependent RCS Measurements in the Presence of Outliers
Coherent radar cross section measurements on a target moving along the line-of-sight in free space will trace a circle centered on the origin of the complex (I,Q) plane. The presence of additional complex signals (such as background, clutter, target-mount interactions, etc.), which do not depend on target position, will translate the origin of the circle to some complex point (I0,Q0). This type of phase-dependent I-Q data has been successfully analyzed. However, the presence of outliers can introduce significant errors in the determination of the radius and center of the IQ circle. Hence, we implement a combination of a robust and efficient Least-Median Square (LMS) and an Orthogonal Distance Regression (ODR) algorithm is used (1) to eliminate or to reduce the influence of outliers, and then (2) to separate the target and background signals. This technique is especially useful at sub-wavelength translations at VHF, where spectral techniques are not applicable since only a limited arc of data is available. We analyze data obtained as an Arrow III target moves relative to its supporting pylon. To demonstrate the effectiveness of the technique, we introduce rf interference signals into S band data and show that the uncontaminated parameters can be recovered with acceptable uncertainties.
Development of a MATLAB Toolbox to Assist in the Process of RCS Range Calibration
Over the past few years, range certification activities have become more commonplace, as industry, government and academia have embraced the process and acted to implement documented procedures at their facilities. There is now a significant amount of documentation laying out the process, as well as templates to assist ranges in developing their range books. To date, however, there have been fewer examples of useful tools to assist the ranges in better understanding how the process will affect their specific range. The authors have developed a first generation MATLAB toolbox designed to provide ranges a “what-if” capability to see the impact of specific range errors on the range’s operations. Included within the toolbox are several types of additive and multiplicative errors, as well as means of modeling various aspects of radar operation.
Cheetah PNA RCS and Antenna Measurement System
System Planning Corporation (SPC) is pleased to announce our new instrumentation radar measurement system denoted the Cheetah radar line. This radar system is based around the new Agilent PNA series of network analyzers. The PNA operates from 0.1 to 67 GHz and is utilized for making gated CW or CW RCS and Antenna measurements. The PNA has a built in synthesizer that allows the unit to be used without costly external synthesizers and external mixers. The PNA also has four identical receiving channels, two signal and two reference, that permit simultaneous co and cross pol measurements to be made. PNA IF bandwidth is selectable from 1 Hz to 40 kHz to optimize measurement sensitivity, dynamic range and speed. Using the segmented sweep feature of the PNA a single frequency sweep can be broken into segments, to further optimize the sensitivity, dynamic range, and speed. Each segment can have its own start and stop frequency, frequency step size, IF BW and power level. SPC has developed the high speed RF gating, low noise RF preamplifiers and high speed digital timing system, which allow maximum sensitivity, full up gated CW or CW radar measurements using the PNA. SPC has coupled the system to the CompuQuest 1541 RCS and Antenna Data Acquisition and Data Analysis Processing Software. This exciting new product line offers reduced cost and improved performance over current network analyzer based systems using the HP 8530, 8510, etc. Performance improvements are in the reduced noise figure, sensitivity, dynamic range and measurement speed. Measurement speeds are increased by at least a magnitude of order over the older systems and in some cases a couple of orders of magnitude.
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