AMTA Paper Archive
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Characterization of a dual circularly polarized, dual plane monopulse, millimeter wave antenna
The characteristics of dual circularly polarized, dual plane monopulse, millimeter wave antennas are being measured at the U.S. Army Redstone Technical Test Center. This paper will describe the instrumentation suite which allows for simultaneous collection of sum and differenee data in both planes. Also discussed is special antenna under test interfacing requirements, and compact antenna test range facilities
Combined pulsed/CW and pulsed-IF instrumentation radar system, A
In response to evolving USAF RCS measurement requirements, Lintex has developed a combined Pulsed/CW and Pulsed-IF instrumentation system for use at the Advanced Radar Cross Section Measurement Range. This instrumentation system, one of Lintek's Model 500 Series, couples the simplicity and high signal-to-noise ration of Pulsed/CW measurements with the flexibility and precise clutter rejection of Pulsed-IF systems. In this paper, a direct comparison of the Pulsed/CR and Pulsed-IF performance is presented. The theoretical sensitivity and throughput of the system as a function of duty cycle in each mode is calculated and compared to the measured results. The Pulsed-IF system is found to have better sensitivity and stability for short-range measurements due to the high PRF capability of this receiver. The Pulsed-IF mode of operation also offers much better sensitivity for measurements made at longer ranges, for which the duty-cycle losses of the Pulsed/CW mode become excessive. The wideband Pulsed-IF mode is also preferred in high-background environments, since precise time-gating may be used to reduce the clutter return. In areas of high RFI, the Pulsed/CW radar system has provided better results due to the narrow receiver bandwidth.
Compact modular instrumentation radar system, A
A compact modular instrumentation radar system has been developed for antenna, RCS, and general RF measurements. The MMS-420 system consists of a single, rack mounted, programmable mainframe controller and display into which a wide range of RF, IF and signal processing modules can be installed. A family of external RF modules has also been developed to support measurements from VHF through millimeter-wave bands. It is designed to function as a stand-alone measurement system, or interface with network analyzers and other external processing equipment. The hardware and software are easy to customize for specialized measurement applications.
High-speed measurement of T/R modules used in phased array antennas
As mobile and satellite phased array antennas move from to concept production the demands on test station throughput increases dramatically. Completely characterizing a Transmit/Receive (TIR) module may require thousands of S-parameter measurements under CW and high-power pulsed conditions, as well as, harmonics, spurious, and noise figure measurements. The measurement throughput of instrumentation used in characterizing the prototype TIR modules simply may not be capable of handling the added volume of a production environment. The volume of measurements, the multiport nature of the device, and the integrated TIR module control make it necessary to reexamine the traditional approaches of separate network analyzers, noise figure meters, and spectrum analyzers. The result is a high-speed modular test ystem that completely characterizes the device in a single connection. The system contains a single receiver and a dedicated controller that utilizes the instrumentation in the most efficient method while maintaining or increasing the accuracy of traditional approaches. This paper describes the high-speed test stations that have been designed and built and are currently in use in several production facilities. Test system architecture is discussed and measurement throughput numbers are given and compared to conventional approaches.
Vertical antenna array applications on a ground-bounce instrumentation radar range
A vertical array of antennas is used to beamform the farfield used in the measurement of Radar Cross Section (RCS) on a ground-bounce radar range. By properly weighting (attenuating) and phasing (through line length adjustments) each antenna, a desired far-field pattern can be obtained. This paper discusses some benefits of the technique and outlines a basic mathematical approach. Implementation is considered, and wide band ramifications of a practical design are discussed. At RATSCAT, this basic understanding was used to examine a simple two element array. This paper preceded that study and was originally written just for that purpose.
Pulsed antenna measurements with the HP 8530A microwave receiver
This paper discusses the instrumentation techniques that can be used for the measurement and characterization of antennas that are to be tested in a pulsed-RF mode of operation. A pulse-parameter chart is presented that illustrates all possible ranges of pulse width and pulse repetition frequencies for antennas operating in a pulsed mode. An antenna operating in a pulse mode will have pulse parameters that lie somewhere on the pulse parameter chart. This paper defines five different measurement regions of the pulse-parameter chart, and presents the measurement techniques for measuring pulsed antennas that operate in each of these regions.
Instrumentation upgrade for ultra-high speed data acquisition in the DASA compensated compact range
Deutsche Aerospace is developing and testing high performance communications antennas for the INTELSAT program. A large number of antenna measurements must be performed, for two polarizations, multiple frequencies and multiple beams. To measure all parameters in a single rotation of the antenna, a highspeed instrumentation system is required. The instrumentation was upgraded using the latest technology in receivers, sources and control systems. Commercially available components were used for all components. The resulting system can perform a complex antenna measurement consisting of over four million data points within only two hours.
Analysis of amplitude dispersion in radar scattering using the MUSIC algorithm
At high frequencies, the scattered fields from a radar target can be modeled as a sum of contri butions from a finite number of scattering centers. We use a parametric model based on the Geometric Theory of Diffraction (GTD) to estimate the location and type of scattering centers present in a frequency domain data set. The parameters of the model are estimated using a modified MUSIC algorithm that incorporates the GTD model. A new spatial smoothing algorithm is also introduced.
Interpretation of area target amplitude and dimensions in ISAR images
The amplitude of a point target observed in an ISAR image is equal to their free space RCS when effective sidelobe windowing is used. Likewise, its location in the image is identical to its actual location. The interpretation of observed amplitude and dimension of area targets is not as easy. The ISAR image of a rectangular flat plate formed by rotating it around its longer axis is significantly different from an ISAR image of the same plate rotated about its shorter axis. Both the amplitude and the size of the plate's image are different. In this paper, the theory of physical optics is reviewed in conjunction with the principles of ISAR processing to explain these differences.
Methods for enhancing the utility and performance of coherent background subtraction
Coherent background subtraction is an established method of reducing additive range clutter in radar cross section measurements. In some measurement situations, it is neither practical nor convenient to directly make a coherent measurement of the range background. The Environmental Research Institute of Michigan has devel oped two methods of synthesizing background measure ments for the coherent subtraction of additive clutter in these cases. The first method synthesizes a background for measurements of pylon-supported targets by remov ing unterminated pylon returns using software gating. The second method improves background subtraction by compensating for phase drift between target and back ground measurements. In this paper, these methods of improving the performance and utility of background subtraction will be described and demonstrated on mea sured data.
Interferometric techniques for discriminating multipath in ground to ground radar diagnostics with minimal constraints on collection geometry
Due to inherent cost, safety and logistical advan tages over dynamic measurements, Ground-to-Ground (G2G, aircraft and radar on tarmac) diagnostic radar measurements may be the preferred method of assessing aircraft RCS for signature maintenance. However, some challenging complications can occur when interpreting SAR imagery from these systems. For example, the effect of ground induced multi-path often results in the measurement of a significantly different image based RCS than would have been obtained by a comparable Ground-to-Air (G2A) or Air-to-Air (A2A) system. Although conventional 2-D SAR images are useful in determining the physical source (down-range/cross range) of scatterers, it is difficult at best to deduce whether an image pixel is a result of direct (desired) or ground induced multi-path (undesired) scattering. ERIM and MRC recently completed an experiment testing the utility of collecting and processing interfero metric (2-antenna) SAR radar data. This effort produced not only high resolution SAR imagery, but also a com panion data set, derived from interferometric phase, which helps to isolate the source (direct or multi-path) of all scattering within the SAR image. Additionally, the data set gives a measure of the physical height of direct scatterers on the target. This paper outlines the experiment performed on a RCS enhanced F-4 aircraft using a van mounted radar. Conventional high resolution imagery (down-range/ cross-range/intensity) will be shown along with down range/height/intensity and cross-range/height/intensity images. The paper will also describe the processing pro cedure and present analysis on the interferometric results. The unique motion compensation processing technique combining prominent point and motion mea surement instrumentation data, eliminates the need for a tightly controlled collection path (e.g. bulky rail sys tems). This allows data to be collected with the van driven somewhat arbitrarily around the target with side mounted antennas taking measurements at desired aspects.
Method to quantify target-support interaction terms, A
Target support interaction terms often drive Radar Cross Section Measurement limitations. These limitations are when mask needed information, or render interpretation difficult. Although support improvement is desirable and studied, there is a fundamental problem. Perhaps we can create a support that is 10 dB better than existing supports. The technology producing that improvement will usually be applicable to targets. Result: The same ratios recur. Modern instrumentation Radar possesses many acquisition agility's. Processing power currently available permits handling huge volumes of data. This paper studies evaluation and/or elimination of interaction terms using these agility's. Interactions within the test article are often significant. Controlled of this method would select and retain, or remove the terms.
Simulation of errors in near-field facilities
A technique for estimating measurement errors in near field facilities is presented. Known mechanical and electrical errors can be accounted for in simulation and such results are presented here. Unknown factors like chamber reflection and instrumentation drift can be estimated via selective measurement and the error induced by such anomalies may be combined with the simulated findings to provide error patterns for a particular test antenna and facility. Results are shown where these patterns are used to calculate measurement error limits. The software presented here also allows the generation of parametric curves which show the impact of a parameter of interest.
Fiber optic link phase thermal noise performance in a coherent bistatic instrumentation radar
Instrumentation grade, coherent, bistatic, radar cross section (RCS) measurement systems require a reliable low-noise method to link the reference, local oscillator (LO) and intermediate frequency (IF) coherent signals between the transmit and receive subsystems. One approach to this is the use of a fiber optic link (FOL). Phase noise measurements have been performed on a distributed feedback (DFB) type laser transmitter-photodiode receiver link with a delay of up to 2.26 kilometers, operating at 5 GHz, using a standard HP 3048A phase noise test measurement setup. System level tests have been performed, incorporating a FOL into a coherent bistatic instrumentation radar system local oscillator path, and performing image processing on an emulated target A first level analysis was conducted regarding the effects of the thermal noise on the radar perfonnance.
Performance of helicopter mounted HF antennas
Finite-Difference Time-Domain (FDTD) is prov ing to be a practical and accurate technique for an alyzing and predicting the performance of anten nas mounted on complex structures. As part of an effort to develop and validate an FDTD code, the impedance and radiation patterns of helicopter mounted loop antennas are predicted and compared to full-scale and 1:10 scale measurements. The input impedance and coupling of HF loop an tennas on the scale model helicopter are measured in the ElectroMagnetic Anechoic Chamber facility at Arizona State University. Although made difficult by the large mismatch between the highly reactive HF antennas and the instrumentation, the scaled impedance measurements agree well with the full scale measurements and predictions. In addition, ro tor blade modulation effects on the input impedance are examined.
Measurement of antennas with integrated electronics
Antennas that are integrated with system electronics extend the measurement scope of conventional, passive antenna designs. At a minimum, the dynamic range of the antenna system as limited by the electronics must be established. Array antennas with active electronics pose additional challenges because unit to unit variations in the array element electronics affect array performance. Other challenges are presented when digital electronics are incorporated into the antenna. Measurement techniques and instrumentation issues are discussed.
3-D imaging of a T-72M at 35 and 95 GHz
Millimeter Wave (MMW) Radar Cross Section (RCS) measurements of full scale ground vehicles are used to develop and validate scattering models for smart weapons applications (target detection, discrimination and classification algorithms) and Hardware-in-the-Loop (HITL) missile simulations. This paper describes a series of MMW RCS measurements performed at Range C-52, Eglin AFB FL on a T-72M in a field environment using an exiting instrumentation radar (with slight modifications to allow for accurate height adjustment) and in-scene phase reference. The test methodology, instrumentation systems, 3-D Imaging Algorithm and sample data sets at 35 and 95 GHz will be presented as well as a detailed sensitivity analysis and discussion of error effects.
Dynamic ground-to-air radar imagery
Dynamic ground-to-air measurement of aircraft RCS has several advantages over static measurements. The target may be measured in flight configuration and the support pylon is eliminated. Although dynamic RCS imagery has been performed since the late 1970s, the cost and complexity of such measurements have limited their utility for routine testing. In this paper, an easily deployable ground-to-air radar imaging system developed by Aeroflex Lintek is presented. This system forms images of aircraft in straight flight, requiring no on-board instrumentation or special pilot training. The radar system, flight profiles, and processing tools required for generating images of aircraft in flight are presented, along with examples of measured target data.
A Cost effective, versatile antenna and radome instrumentation test system
A cost-effective, versatile instrumentation system for measuring antennas and radomes is described. The system features the use of high load capacity, high accuracy stepper motor based positioners as the primary system axes. The system is capable of being easily reconfigured to perform tests on antenna/radome systems with antennas fixed relative to the radome, or with the antenna and radome capable of movement relative to one another. Measurements may be performed at RF, IF or baseband, depending on the portions of the seeker or monopulse assembly to be included in the test. The system also contains analysis capabilities that simulated mode forming and beam forming functions to isolate antenna effects.
Measurement considerations for antenna pattern accuracy
This paper examines antenna measurement errors attributable to instrumentation, and their effect on measurement uncertainty.
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