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Over the last few years, we have implemented several methodologies pertaining to uncertainty analysis of RF and Optical measurements. These methodologies are currently in use within the radar cross-section, electro-optic/infrared, and material measurement laboratories at the Air Force Research Laboratory. In this paper we discuss from a top level some of the approaches we have implemented, and identify some important issues one needs to address before beginning an uncertainty analysis. We illustrate one such approach as it applies to the estimation of radar cross-section uncertainty.
A first analysis of the equivalences between Multiple Input Multiple Output (MIMO) and physical/synthetic radar arrays is presented. The establishment of these equivalences is addressed to make use of efficient radar imaging algorithms, which were originally conceived for SAR systems, with MIMO arrays. The main advantage of MIMO arrays is that, with a reduced cost and complexity of the antenna feeding network, they offer imaging capabilities very close to those of SAR and physical radar arrays. This makes MIMO radar a very interesting option in real-time imaging applications (e.g., surveillance of small areas). The paper will present some numerical simulations using some reference scenarios where the imaging capabilities of MIMO arrays will be assessed. A comparative analysis with the well-known SAR and uniformly spaced radar arrays will be presented. Here the study is made with one-dimensional radar apertures, and subsequently will be extended to two-dimensional radar apertures. The analysis of the performance of the MIMO arrays is based on a Matlab simulation tool that is used to optimize the array topology and also to form the radar images of a synthetic scenario. The optimization technique is based on a genetic algorithm, using a fitness function measuring the degree of uniformness and uniqueness of the loci of the phase centers of the tx/rx pairs of the MIMO array. Results show that the found topologies show a performance close to uniformly spaced physical radar arrays.
A real-time S-band radar imaging system will be shown in this paper that uses a spatially diverse antenna array connected to a highly sensitive linear FM radar system and uses a synthetic aperture radar (SAR) imaging algorithm to produce real-time radar imagery. The core of this radar system is a high-sensitivity, range gated, radar architecture. Previous work has demonstrated the effectiveness of this radar architecture for applications requiring low-power and high sensitivity for imaging through lossy dielectric slabs at S-band and in free space at both S and X bands. From these results it was decided to develop a real-time S-band SAR imaging system. This is achieved by constructing a spatially diverse antenna array that plugs directly into a pair of S-band transmit and receive radar front ends; thereby providing the ability for real-time SAR imaging of objects. The radar system chirps from approximately 2 GHz to 4 GHz at various rates from 700 microseconds to 10 milliseconds. Transmit power is adjustable from approximately 1 milliwatt or less. The image update rate is approximately one image every 1.9 seconds when operating at a chirp rate of 2.5 milliseconds. This system is capable of producing imagery of target scenes made up of objects as small as 1.25 inch tall nails in free space without the use of coherent integration. Previous applications for this radar system include imaging through dielectric slabs. It will be shown in this paper that this radar system could also be useful for real-time radar imaging of low RCS targets at S-band.
This paper describes how the Dynamic Advanced Radar Test (DART) facility was designed, constructed, integrated and validated within budget in a 12-month time frame using lean engineering techniques. The facility is a world-class Radar seeker test facility. These techniques allowed the DART team to enhance capabilities without adding cost or complexity. The purpose of this paper is to identify a new paradigm in Radio Frequency (RF) range development, whereby all variables are accounted for early in the process, thus preventing and avoiding time consuming and costly mistakes. This process relies on lean engineering Accelerated Improvement Workshops (AIW) and Production, Preparation, Process (3P) workshops to guide the design process. Allowing all stakeholders to be owners through these intense workshops is vital. Additionally since formal evaluation tools and methodologies guide the workshops, improvement opportunities are maximized while minimizing risk.
Active phased array antennas are often considered for many applications in radar and communications, particularly in millimeter wavelengths. The ability of active phased array antennas to be reconfigured with different beam shapes and pointing directions makes them attractive to increase the flexibility of the next generation of communications satellites so that they can adapt to the needs of a fast changing communications market. The antenna noise temperature of an active array is an important performance parameter, which is difficult to measure compared to a classical passive antenna. Moreover, for a satellite antenna, which has to be evaluated in an anechoic chamber before integration on the spacecraft, the ability to characterise the noise contribution of the antenna itself independent of the environment noise would be very interesting as it would allow better prediction of the antenna performance when it is deployed in orbit on the spacecraft. The paper describes the results of a study undertaken for the French Space Agency (CNES) to devise a new method for the measurement of the noise temperature of a Ka band active phased array antenna when mounted in a Compact Antenna Test Chamber (CATR). An important objective of the study was to find a method which did not rely on the substitution of the antenna under test with a reference antenna, which is the method often used in practice. The method of measurement of noise was based on digital processing of signal to noise ratio rather than analogue detection of noise level, which improves the measurement precision.
Measurement of the antenna pattern of the Haystack Auxiliary Radar (HAX), an experimental Ku band radar system developed by the Massachusetts Institute of Technology Lincoln Laboratory for deep space experimentation, was recently carried out utilizing a ground based, mobile recording system. The HAX radar system uses a 12.19 m parabolic antenna placed inside of a radome which is located on Millstone Hill in Westford, Massachusetts. The recording system, which includes a Ku-band analog front end and a high-speed digitizer with 500 MHz instantaneous bandwidth and long duration recording capability, was located at the summit of Mt. Wachusett, 36.1 km southwest of HAX. Several azimuth and elevation antenna pattern cuts were acquired by transmitting towards a wide-band ground based recording system placed down range while rotating the HAX antenna. Throughout these pattern measurements the radar was operated in a reduced power pulsed CW mode. Continuous wide-band recordings from the slowly scanned pattern measurements were taken and the data was processed to detect individual pulses, retaining only the portions of the recordings containing detected pulses. Post-processing of the pulsed CW data allowed for measurement of the antenna pattern with a significant dynamic range, characterizing both the mainbeam of this antenna and the far-out sidelobes.
A device and algorithm of measuring of microwave airborne radar antenna impedance and input power level are presented. A compact five-port microwave reflectometer, p-i-n diodes switch, single microwave detector are used. The output detector signal is processed. All of that results in decreasing of the cost of equipment, elimination of instrument components non-ideality and reaching of high equipment accuracy.
This paper deals with characterization of passive ultra-high frequency (UHF) radio frequency identification (RFID) tag performance. Tag’s energy harvesting properties and the significance of the backscattered signal strength and radar cross section (RCS) of the tag are discussed using two examples: dipole tag antennas of various widths and identification of industrial paper reels.
Commercial windmill driven power turbines (“Wind Turbines”) are expanding in popularity and use in the commercial power industry since they can generate significant electricity without using fuel or emitting carbon dioxide “greenhouse gas”. In-country and near-off shore wind turbines are becoming more common on the European continent, and the United States has recently set long term goals to generate 10% of national electric power using renewable sources. In order to make such turbines efficient, current 1.5 MW wind turbine towers and rotors are very large, with blades exceeding 67 meters in diameter, and tower heights exceeding 55 meters. Newer 4.5 MW designs are expected to be even larger. The problem with such large, moving metallic devices is the potential interference such structures present to an array of civilian air traffic control radars. A recent study by the Undersecretary of Defense for Space and Sensor Technology acknowledged the potential performance impact wind turbines introduce when sited within line of site of air traffic control or air route radars. [1]. In the Spring of 2006, the Air Force Research Laboratory embarked on a rigorous measurement and prediction program to provide credible data to national decision makers on the magnitude of the signatures, so the interference issues could be credibly studied. This paper, the first of two parts, will discuss the calibrated RCS measurement of the turbines and compare this data (with uncertainty) to modeled data.
The DGA/CELAR (France) (Centre d'Electronique de l'Armement: French Center for Armament Electronics) is able to measure targets in order to get their RCS (Radar Cross Section). Yet CELAR RCS measurement facilities are not compact bases and therefore the measured field is a near field. This article proposes a solution allowing the transformation of this near field to a far field and this in the three dimensions of space without limiting any dimension with Fraunhöfer criterion. Thanks to this method the RCS of a target is able to be known in any direction of space and moreover the calculation of a three-dimensional ISAR (Inverse Synthetic Aperture Radar) picture is thus possible. At first the theoretic part of our work is presented. Then a fast method in order to calculate the transformation of a near field to a far field by optimising the calculation time thanks to signal processing theory is given. Finally obtained results from simulated bright points are presented.
The DGA/CELAR (France) (Centre d'Electronique de l'Armement: French Center for Armament Electronics) is able to measure targets in order to get their RCS (Radar Cross Section). Once this RCS is acquired it may be very interesting to calculate RADAR pictures of these targets because RADAR picture allows emphasizing the bright points. Until now, CELAR produced images in two dimensions, but these pictures have shown their limits in order to locate problems in altitude. This article fills this gap while proposing two methods in order to get an image in three dimensions: a method using a three-dimensional Fourier transform and a method based on interferometry.
The Microwaves and Radar Institute regularly performs calibration campaigns for spaceborne synthetic aperture radar (SAR) systems, among which have been X-SAR, SRTM, and ASAR. Tight performance specifications for future spaceborne SAR systems like TerraSAR-X and TanDEM-X demand an absolute radiometric accuracy of better than 1 dB. The relative and absolute radiometric calibration of SAR systems depends on reference point targets (i. e. passive corner reflectors and active transponders), which are deployed on ground, with precisely known radar cross section (RCS). An outdoor far-field RCS measurement facility has been designed and an experimental test range has been implemented in Oberpfaffenhofen to precisely measure the RCS of reference targets used in future X-band SAR calibration campaigns. Special attention has been given to the fact that the active calibration targets should be measured under the most realistic conditions, i. e. utilizing chirp impulses (bandwidth up to 500 MHz, pulse duration of 2 µs for a 300 m test range). Tests have been performed to characterize the test range parameters. They include transmit/receive decoupling, background estimation, and two different amplitude calibrations: both direct (calibration with accurately known reference target) and indirect (based on the radar range equation and individual characteristics). Based on an uncertainty analysis, a good agreement between both methods could be found. In this paper, the design details of the RCS measurement facility and the characterizing tests including amplitude calibration will be presented.
Till recently, the testing of installed aircraft radars antennas and radomes required the dismantle of the units from the aircraft in order to measure theirs electromagnetic properties inside a classical anechoic chamber. Such operations were difficult, particularly time consuming and did not fully characterize the antenna within its operational environment. For these reasons, ELTA issued a request for an “in situ” spherical near-field test system that could be used for “on board testing of radars” located inside the nose of an aircraft. SATIMO responded with a solution based on its own proprietary rapid probe array technology already employed extensively worldwide for antenna testing. The facility was recently delivered to ELTA and “in-situ” measurement of a radar antenna and radome were performed (fig.1&2). This new generation of test system performs multi-beam, multi port and multi-frequency dual polarized complex measurements at a step of 3-degree in azimuth and elevation over a full hemisphere in a few minutes. It is fully autonomous and mobile so it can be used indifferently indoor or outdoor. Continuous wave or pulsed electromagnetic measurements are obtained thanks to an advanced software which allows the user to control the main radar parameters. Diagnostic of faulty elements in the radar is also possible through a special automated measurement mode. The antenna test system has been completed and validated through a detailed acceptance test plan including inter comparison with a traditional planar near field test range. This paper presents the general design consideration and a summary of the results of the extensive verification tests.
The dynamic range of a measurement system is typically evaluated in the frequency domain. However, for radar-cross-section (RCS) measurements, time processing of the frequency-domain data is often utilized to determine the temporal or spatial (down-range) location of responses. Dynamic range in the time domain is thus of considerable importance in determining what range of responses can be resolved and identified. While the coherent integration inherent in the pulse-compression process can increase the time-domain dynamic range beyond that of the frequency-domain, non-linearity in the measurement system leads to signal-dependent noise which, in turn, limits the time-domain dynamic range to a much smaller value. Thus, specification and characterization of time-domain dynamic range is critical for understanding the linearity requirements and the time-domain capability of the measurement system. This paper reviews design considerations, error sources, and measurement methods relevant to optimizing dynamic range in the time domain. Examples of time-domain measurements are included.
This paper describes a new approach to improving the low frequency reflectivity performance of geometric transition radar absorbent materials through the use of impedance loading in the form of one or more included FSS layers. The discussion includes theoretical predictions and measured data on modified commercially available RAM which confirm the validity of the concept.
Techniques for measuring the radar cross section (RCS) of a target in a controlled environment are well known and established and many commercial systems are available for making these measurements. However, when RCS measurements need to be taken in a variable environment – such as over the ocean – several important issues are introduced that need to be carefully considered before a meaningful measurement can be made. This paper shall discuss some of these issues and present a measurement approach that appears to reduce the uncertainty that these factors introduce.
This paper discusses the Blue Airborne Target Signatures (BATS) database. BATS is the United States Air Force central repository for US and allied signature data. It resides at and is maintained by the Signatures Element, 453rd Electronic Warfare Squadron, Air Force Information Warfare Center, Lackland AFB TX. BATS contains radar cross section (RCS), infrared (IR), and antenna pattern (AP) data, both measured and simulated. The history and background of BATS is also presented, as well as current activities.
This paper describes the motivation and major issues related to the design of an RCS radar instrumentation system for use in a compact range. The high degree of sophistication implemented in commercially-available radar systems renders them subject to significant MTTR (mean time to repair) with corresponding losses in range productivity. The objective of the design effort was to develop a system of minimal complexity, maximally suited to troubleshooting and repair by laboratory personnel, while retaining the operational efficiency normally provided by the commercial systems.
Using a discarded garage door opener, an old cordless drill, and a collection of surplus microwave parts, a high resolution X-band linear rail synthetic aperture radar (SAR) imaging system was developed for approximately $240 material cost. Entry into the field of radar cross section measurements or SAR algorithm development is often difficult due to the cost of high-end precision pulsed IF or other precision radar test instruments. The low cost system presented in this paper is a frequency modulated continuous wave radar utilizing a homodyne radar architecture. Transmit chirp covers 8 GHz to 12.4 GHz with 15 dBm of transmit power. Due to the fairly wide transmit bandwidth of 4.4 GHz, this radar is capable of approximately 1.4 inches of range resolution. The dynamic range of this system was measured to be 60 dB thus providing high sensitivity. The radar system traverses a 96 inch automated linear rail, acquiring range profiles at any user defined spacing. SAR imaging results prove that this system could easily image objects as small as pushpins and 4.37 mm diameter steel spheres.
We use a rotating dihedral to determine the cross-polarization ratios of radar cross section measurement systems. Even a small amplitude drift can severely degrade the calibration accuracy, since the calibration relies on accurate determination of polarimetric data over a large dynamic range. We show analytically how drift introduces errors into the system parameters, and outline an analytic procedure to minimize the in.uence of drift to estimate system parameters with greater accuracy. We show that only very limited information about the drift is needed to provide measured system parameters accurate to second order in the error-free parameters. Higher-order accuracies can be achieved by using more detailed information about the drift. We use simulations to explain and illustrate the analytic development of this theory. We also show that, using cross-polarimetric measurements on a cylinder, we can recover the exact system parameters. These .ndings show that we can now calibrate polarimetric radar cross section systems without the large uncertainties that can be introduced by drift.