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E-2C APS-125 Radar In-Flight Antenna Measurement Techniques
The E-2C Hawkeye aircraft is a carrier based airborne early warning sensor platform. The primary sensor is the APS-125 radar which is operated in the 400 to 446 MHz frequency range and utilizes a 10-element, Yagi end-fired array antenna integrated into a rotating, 2,400 pound rotodome mounted on top of the E-2C aircraft. As is the case for most airborne antennas, the performance in free space when the antenna is off the aircraft can be readily measured on a ground antenna range, but the accurate measurement of the antenna’s performance under actual flight conditions presented project engineers with a unique problem: Pattern interaction between the rotating rotodome and the aircraft fuselage and turning propellers could not be evaluated using existing ground range facilities. The proposed improvements to these facilities to accomplish this task were estimated to cost in excess of five million dollars.
An Automated Precision Microwave Vector Ratio Measurement Receiver Offers Solutions for Sophisticated Antenna Measurement Problems
This paper describes a new, automated, microprocessor controlled, dual-channel microwave vector ratio measurement receiver for the frequency range 10 MHz to 18 GHz. It provides a greater than 120 dB dynamic range and resolutions of 0.001 dB and 0.1 degree. Primarily designed as an attenuator and Signal Generator Calibrator, it offers solutions to antenna measurement problems where high accuracies and/or wide dynamic measurement ranges are required such as for broadband cross-polarization measurements on radar tracking antennas, highly accurate gain measurements on low-loss reflector antennas, frequency domain characteristics measurements on wide-band antennas with resulting data suitable for on-line computer conversion to time domain transient response and dispersion characteristics data and wideband near field scanning measurements for computing far field performances. The measurement data in the instrument is obtained in digital form and available over an IEEE-488 bus interface to an outside computer. Measurement times are automatically optimized by the built-in microprocessor with respect to signal/noise ratio errors in response to the measurement signal level and the chosen resolution. Complete digital measurement data amplitude of both channels and phase, is updated every 5 milliseconds.
High sensitivity millimeter wave instrumentation
This paper describes a technique to increase the millimeter-wave sensitivity of the popular 1740-1750 series SA (Scientific-Atlanta) receivers. The frequency coverage is conveniently extended with harmonic mixing techniques which reduce the sensitivity. Phase-locked circuitry was developed to allow the receiver to operate in a fundamental mixing mode which permits the measurement of millimeter-wave antennas and radar targets with the same sensitivity achieved at microwave frequencies. At Ka-band a 30 dB enhancement in sensitivity results with the phase-locked circuitry compared with the conventional instrumentation.
US Army Electronic Proving Ground
The US Army Electronic Proving Ground is in Southeastern Arizona with outlying facilities located throughout Southern Arizona. The Proving Ground is an independent test and evaluation activity under the command of the US Army Test and Evaluation Command. It was established in 1954. EPG’s role in the material acquisition cycle is to conduct development (DT I & II), initial production (first article), and such other engineering (laboratory-type) tests and associated analytical studies of electronic materiel as directed. The results (reports) of these efforts are used by the developer to correct faults, and by Army and DOD decision-makers in determining the suitability of these materiels/systems for adoption and issue. Customer tests to satisfy specific customer requirements and foreign materiel exploitations are also done. EPG is assigned test responsibility for Army ground and airborne (aircraft-mounted) equipment/systems which utilize the electromagnetic spectrum to include: tactical communications; COMSEC (TEMPEST testing included); combat surveillance, and vision equipment (optical, electro-optical, radar, unattended sensors); intelligence acquisition; electronic warfare; radiac; imaging and image interpretation (camera, film, lens, electro-optical); camouflage; avionics; navigation and position location; remotely piloted vehicle; physical security; meteorological; electronic power generation, and tactical computers and associated software. Facilities and capabilities to perform this mission include: laboratories and electronic measurement equipment; antenna pattern measurement’ both free-space and ground-influenced; unattended and physical security sensors; ground and airborne radar target resolution and MTI; precision instrumentation radars in a range configuration for position and track of aerial and ground vehicles; climatic and structural environmental chambers/equipment; calibrated nuclear radiation sources; electromagnetic compatibility, interference and vulnerability measurement and analysis; and other specialized facilities and equipment. The Proving Ground, working in conjunction with a DOD Area Frequency Coordinator, can create a limited realistic electronic battlefield environment. This capability is undergoing significant development and enhancement as a part of a program to develop and acquire the capability to test Army Battlefield Automation Systems, variously called C3I, C4, and/or CCS2 systems. The three principal elements of this capability which are all automated include: Systems Control Facility (SCF), Test Item Stimulator (TIS), and Realistic Battlefield Environment, Electronic (REBEEL). In addition to various instrumentation computers/processors, EPG currently utilizes a DEC Cyber 172, a DEC VAX 11-780, a DEC System 10, and has access to both a CDC 6500 and a 6600. Under the Army Development and Acquisition of Threat Simulators (ADATS) program, EPG is responsible for all non-air defense simulators. The availability of massive real estate in Southern Arizona, which includes more than 70,000 acres on Fort Huachuca, 23,000 acres at Willcox Dry Lake, and 1.5 million acres near Gila Bend, is a major factor in successful satisfaction of our test mission. Fort Huachuca itself is in the foothills of the Huachuca Mountains at an elevation of approximately 5,000 feet and has an average annual rainfall of less than 15 inches. Flying missions are practical almost every day of the year. The Proving Ground is ideally situated between two national ranges and provides overlapping, compatible instrumentation facilities for all types of in-flight test programs. The clear electromagnetic environment, the excellent climatic conditions, and the freedom from aircraft congestion make this an unusually fine area for electronic testing. The Proving Ground consists of a multitude of sophisticated resources, many of them unique in the United States, which are an integral part of the USAEPG test facility and have resulted from an active local research and development effort over a 28-year period.
High resolution instrumentation radar
The development of a high resolution instrumentation radar is described. This radar constructed at X-band uses a chirp waveform to achieve a 4.9” range resolution capability. A key feature of this development is the use of cos2 x amplitude weighting to control the range sidelobes. An example of a high resolution radar response is described.
A Microwave interferometer technique for RCS and phase measurements
The radar scatter matrix can be accurately characterized in magnitude, relative phase, and polarization for both far-field monostatic and bistatic conditions by means of a microwave interferometer. A separate transmitting antenna illuminates the target of interest while two adjacent receiving antennas measure magnitude and the combine in a phase comparator whose output is a phase differential caused by a changing target aspect angle. Using correct constants and scale factors this differential is integrated to provide target phase information. Different polarizations are obtained by switchable feeds. The technique can be used on an RCS range under static conditions or under dynamic conditions with a ground based radar and an airborne target. The advantage gained is that errors due to radar path length changes are eliminated.
Measurement of surface coupled antennas for subsurface radar probing
The experimental techniques presented here can be used to obtain the approximate time domain transfer function and pattern of underground radar antennas. These techniques provide an easy approach to obtaining relative antennas performance. The experimental setup which is used to perform these experiments consists of slanted hollow plastic pipes bored in the ground, the receiver unit, transmitter unit, controller and processor units etc. A buried antennas is used to transmit to a test antenna on the ground surface. The data obtained from two separate test antennas are presented and compared.
A CW radar cross-section measurement facility in X-band
A monostatic C.W. radar cross-section facility in the X-band at the Radar and Communication Centre, Indian Institute of Technology, Kharagpur, India is described. This set up is capable of automatically measuring the c.w. monostatic radar cross-section over the range of aspect angle 0 to ±180o for both TE and TM polarizations. The transmitting/receiving antenna and the rotating target is housed on the roof-top of the building and the microwave circuit with recording arrangement is in the air-conditioned laboratory. It is capable of handling a target of arbitrary shape of maximum size equal to 70 cm and uses a two-stage background (without target) cancellation technique employing Magic-T. A typical value of effective isolation between the transmitted and received signals is of the order of 70 dB and a dynamic range of 35 dB. Measurements made in this set up with different types of targets show a fair agreement with the results obtained by analytical investigations. The same set-up with necessary modifications for measuring the phase of the scattered field along with the amplitude data is expected to provide the amplitude and phase information for target identification and classification problems.
Antenna coordinate system transformations for far field measurements of vehicle mounted antennas
Far field antenna radiation patterns of vehicle mounted antennas are often recorded on the antenna range by rotating the entire vehicle/antenna system with a multiple axis vehicle positioner. Antenna patterns, obtained in this manner, consider the antenna and vehicle as a system and include the effects of the vehicle structure. These patterns are more representative of the operational antenna patterns than the “free space” patterns of the antenna itself. When the antenna is arbitrarily directed on the vehicle, standard antenna pattern cut trajectories, recorded in the coordinate system of the vehicle, become skewed when referenced to the coordinate system of the antenna. With proper adjustment of the fixed angles of the vehicle positioner however, selected standard antenna pattern cut trajectories, referenced to the antenna, may be obtained. The required fixed vehicle positioner angles are obtained from solutions to systems of equations representing the coordinate transformations for the positioner/vehicle/antenna system. In this paper, two general methods of obtaining the coordinate transformation equations are reviewed. These equations are then solved to obtain expressions for the positioner angles necessary for specific cut trajectories. A practical example of a six axis transformation associated with measurements of a three axis gimballed aircraft mounted radar antenna and a three axis vehicle positioner is used to illustrate the techniques (This example was taken from a recent RADC/Newport measurement program.
Conceptual Analysis of Radar Cross-Section Measurements on Compact Ranges
A strong emphasis is now being placed on techniques for reduction of radar cross-section. A missile or aircraft which is invisible to radar has an important strategic advantage. With this fact in mind, the user of a weapons system may place an upper limit on the radar cross-section that he will permit his missile or aircraft to have. The designer must then make use of “stealth technology” to reduce the cross-section to an acceptable level. In order to verify the design, radar cross-section measurements must be made. Thus the current emphasis on cross-section reduction leads to an important need for accurate and reliable methods of measuring radar cross-section.
Drift and background reduction in radar cross section measurements by direct phasor subtraction
Background reflections from range features are a major source of error in Radar Cross Section measurements. Direct phasor subtraction of the background is possible only if the background signals prior to and after target mounting are relatable. If a complex drift, a, is allowed, use of a four-measurement technique, including a reference, can permit elimination of both a and the background.
The Ohio State University compact radar cross-section measurement range
This paper discusses the development and performance of a compact radar cross-section measurement range for obtaining backscattered signatures and patterns on targets up to 1.3 meters in extent, and at frequencies of 1 to eventually 100 GHz. The goal for the development was a general purpose but state of the art range which could obtain the complex radar signature vs. polarization, frequency, and target look angle for both Non-Cooperative Target Rcognition studies and Radar Cross-Section Control Studies. Since the facility was at a University, there were also concerns of cost, versatility, and ease of use in research programs by graduate students. The architecture and some design data on the system are discussed in section 2.
Dynamic radar cross section measurements
There is a continuing need for radar cross section (RCS) measurements of targets of military interest. Such measurements are used in predicting detection performance of radars, in quantifying new radar system performance, in designing protective ECM envelopes of aircraft and ships, and in quantifying changes in RCS modification programs. There is, in addition, an interest in determining the actual radiated pattern of an avionic antenna installed on an airframe. While the system and techniques being described here have been used to support all those uses, the system was designed initially with only RCS measurements in mind.
Wideband radar cross section diagnostic measurements
This paper describes a diagnostic RCS measurement system which uses a low-power, wideband, linear-FM radar to provide RCS responses of targets as a function of frequency, range, cross range, and angle. Range and frequency responses are produced by using an FFT analyzer and a desktop computer to perform on-line signal processing and provide rapid access to final results. Two-dimensional maps of the target RCS distribution in range and cross range are obtained by offline processing of recorded data. The system processes signals resulting from a swept bandwidth exceeding 3GHz to provide range resolution of less than 10 cm. The various operating modes of the instrumentation provide a powerful tool for RCS diagnostic efforts in which individual scattering sources must be isolated and characterized. Several examples of experimental results and presented to demonstrate the utility and performance limits of the instrumentation. The examples include results obtained from measurements of a number of simple and complex shapes and of some commercially available radar absorbing materials.
An Antenna Test Range for Satellite Payload Tests
Conventional antenna test techniques – both far field “slant ranges” and near field – pose limitations for radiative RF testing of satellite antennas and payload systems, of increasing complexity in terms of size, operating frequencies, configurations and technology, particularly when such systems need to be evaluated in their “in-situ” locations on typical satellite platforms, in their flight configurations. Often, combination of tests and simulation has been the only recourse for evaluating system performance. In this paper, a methodology is proposed to achieve these test objectives via the use of a suitable configures, wideband, large (Quiet zone 7m x 5m x 5m), compact range for evaluation od system parameters like E.I.R.P., G/T, C/I, BER, and RF sensing performances. The test plan and evaluation schemes appropriate for these tests are elaborated to demonstrate the validity and usefulness of the approach. For some specific parameters like C/I (for a multibeam payload system) and the radar parameters (for a satellite borne radar system), it turns out that the proposed test methodologies offer the only realistic and complete tool for evaluating such system at satellite level.
High speed measurement receiver
This paper describes a digitally controlled receiver-recorder capable of time division multiplexing in the frequency domain at a 400 KHz rate and in the amplitude domain at a 20 MHz rate. Good sensitivity and interference rejection are other features of this receiver which operates over the 2-18 GHz band. It is utilized to obtain a measure of antennas performance as impacted by air frames upon which the antenna(s) are mounted.
VHF antenna range design
The design concept for outdoor antenna ranges operated at frequency 50 MHz is discussed. The antenna range is designed for test of VHF antennas mounted on a full-scale satellite mockup. Due to the large size of test objects, a tradeoff between cost and test accuracy among carious range configurations is addressed. Due to near-omni directional characteristics of test antennas, the multipath interference may be severe. The interference ground reflection, surface wave and multiple scattering are quantified and evaluated.
A Broadband RCS measurement system
The fast fourier transform capabilities of the Hewlett-Packard 8510 Network Analyzer provide the basis for an RCS measurement system covering the 50 MHz to 26 GHz frequency range. When used in the broadband mode, fine range resolution is achieved. Vector subtraction and gating capabilities permit the acquisition of accurate data in the presence of strong range reflections. Combining this instrument with a high speed data collection and analysis system yields a powerful RCS measurement capability.
Polarization correction of spherical near-field data
This paper describes the relationship of probe polarization correction to probe-pattern corrected and non-probe-pattern-corrected spherical near-field measurements. A method for reducing three-antenna polarization data to a form useful for polarization correction is presented. The results of three-antenna measurements and the effects of polarization correction on spherical near-field measurements are presented.
Automated wideband, phase coherent polarimetric radar cross section measurements
This paper describes the equipment, mechanics and methods of one of the outdoor ranges at Teledyne Micronetics. A computer controlled microwave transceiver uses pulsed CW over a frequency range of 2-18 GHz to measure the amplitude, phase and polarization of the signal reflected off the target. The range geometry, calibration and analysis techniques are used to optimize measurement accuracy and characterize the target as a set of subscatterers.
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