Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
This paper will discuss the need for performance verification, or calibration, of the transmitter and receiver systems used in an antenna or RCS range. Errors introduced by the range and positioning system means the instrumentation’s performance must be measured independently of the range and positioner.
The performance verification should insure that the measurement system exceeds the manufactures’ specifications by a reasonable margin. The verification must be performed with the equipment installed on the range to insure adequate performance on the range. The system must als be verified as a system, rather than individual instruments. This guarantees that measurement errors in each instrument will not add together to exceed the system’s specifications.
Testing of the system should be easy and repeatable to insure accuracy of the verification by the test technician. The tests should also be documented for later reference. The measurements should be traceable to a local standard such as NIST to certify the accuracy and stability of the measurement. The verification should be repeated on a regular basis to insure continued accuracy of the measurement system.
D.N. Black (Georgia Institute of Technology),E.B. Joy (Georgia Institute of Technology),
M.G. Guler (Georgia Institute of Technology),
R.E. Wilson (Georgia Institute of Technology), November 1991
The accuracy of antenna measurements can be improved by compensating for the effects of extraneous fields present in an antenna range using analytical compensation techniques. Range field compensation is a new technique to provide increased measurement accuracy by compensating for extraneous fields created by refection and scattering of the range antenna field from fixed objects in the range and by leakage of the range antenna RF system from a fixed location in the range. The range antenna field must be the dominant field in the range, and the range field cannot change for different AUTs. Existing compensation techniques are limited in the amount of compensation they can provide. The range field is measured over a spherical surface encompassing the test zone using a low gain probe. The measured range field is used in subsequent antenna measurements to compensate for the effects of extraneous fields. This technique is demonstrated using measurements simulated for an anechoic chamber far-field range.
O.M. Caldwell (Scientific-Atlanta Inc.), November 1991
An assessment of instrumentation error sources and their respective contributions to overall accuracy is essential for optimizing an electromagnetic field measurement system.
This study quantifies the effects of measurement receiver signal processing and the relationship to its transient response when performing measurements on rapidly varying input signals. These signals can be encountered from electronically steered phased arrays, from switched front end receive RF multiplexers, from rapid mechanical scanning, or from dual polarization switched source antennas.
Numerical error models are presented with examples of accuracy degradation versus input signal dynamics and the type of receiver IF processing system that is used. Simulations of far field data show the effects on amplitude patterns for differing rate of change input conditions. Criteria are suggested which can establish a figure of merit for receivers measuring input signals with large time rates of change.
G. Hindman (Nearfield Systems Incorporated), November 1991
Portable near-field measurement systems can provide significant flexibility to both large companies seeking to increase their antenna test capabilities, and small companies looking for their first investment in a test range. There are many unique applications for portable near-field antenna measurement systems in addition to their use for standard antenna performance measurements. Some additional applications include flight-line testing, anechoic chamber quiet zone imaging, and EMI testing.
Many of NSI’s near-field systems have been portable designs, capable of being set up in a small lab or office and easily relocated. Key features required for use of a portable system are rapid setup, simplicity of use, low cost, and accuracy. This paper will be focused on practical experience with installing, calibrating, and operating portable near-field measurement systems. It will also cover tradeoffs in their design, and usage in a variety of applications.
L.A. Muth (National Institute of Standards and Technology), November 1991
A recently developed analytic technique that can correct for probe position errors in planar near-field measurements to arbitrary accuracy [1] is shown to be also applicable to spherical near-field data after appropriate modifications. The method has been used to successfully remove errors in the near-field, hence leading to more accurate far-field patterns, even if the maximum error in the probe’s position is as large as 0.2?. Only the error-contaminated near-field measurements and an accurate probe position error function are needed to be able to implement the correction technique. It is assumed that the probe position error function is a characteristic of the near-field range, and that it has been obtained using state-of-the-art laser positioning and precision optical systems. The method also requires the ability to obtain derivatives of the error contaminated near-field defined on an error-free regular grid with respect to the coordinates. In planar geometry the derivatives are obtained using FFTs [1], and, in spherical geometry, one needs to compute derivatives of Hankel functions for radical errors, and derivatives of the spherical electric and magnetic vector basis functions for errors in the ? and Ø coordinates. The error-correction technique has been shown to work well for errors in and of the spherical coordinates r, ? or Ø. Efficient computer codes have been developed to demonstrate the technique using computer simulations.
S. McMillan (Ball Communication Systems Division), November 1991
Phase relationships between the three dominant modes on a four armed spiral can be used to perform broad band, direction of arrival estimates, but this requires accurate estimates of the phase behavior of the antenna both in the design stage and for calibration purposes. Unfortunately, imperfections in range design make the measurement and interpretation of phase information extremely difficult. This paper describes an approach where the imperfections of the range and the behavior of the antenna are modelled, and range effects removed from antenna data through antenna motion, and frequency change. This technique obtained tremendous accuracy at the cost of large amounts of data processing.
J. Lemanczyk (Technical University of Denmark),O. Breinbjerg (Technical University of Denmark),
R. Torres (ESA-ESTEC-XEE), November 1991
Antenna specifications for space applications are very stringent in most cases requiring that antenna measurement facilities be validated before testing can proceed. One method by which this validation can be achieved is by means of antenna test range intercomparisons which entail the measurement of a suitable test antenna at several ranges wherein one range acts as a control laboratory. The problems of such an intercomparison manifest themselves in the availability of suitable validation antennas as well as a clear definition of test parameters and the standardization of comparison procedures to ensure accuracy, reliability and consistency. The several test range intercomparisons carried out by the Technical University of Denmark (TUD) under contract from the European Space Agency (ESA) provide the basis for the current effort under ESA contract to define a suitable validation antenna, design and acquire an antenna for 12 GHz operation as well as defining a Verification Test Plan.
Superresolution (SR) processing techniques have been used for many years in direction finding applications. These techniques have proved valuable in extracting more information from a limited data set than conventional Fourier analysis would yield. SR techniques have recently proven to be an extremely powerful radar cross section (RCS) analysis tool. Typical resolution improvements of 2 to 30 times may be achieved over conventional Fourier-based range domain data in both the one-dimensional and two-dimensional image domains. Typical measurement scenarios which can most benefit from SP processing are presented. These include: VHF/UHF RCS measurements, measurement of resonant targets, and performing detailed scattering analysis on complex bodies. Measurement examples are presented illustrating the use of SR processing in a variety of test conditions. When the advantages of SR processing are combined with the accuracy of Fourier techniques, a new window is opened through which target scattering characteristics can be seen more clearly than ever.
G. McCarter (Hewlett-Packard Company), November 1991
To achieve optimum measurement accuracy and range throughput in antenna and radar cross-section (RCS) measurement applications requires a careful and thorough design of the measurement system.
Measurement accuracy requirements, test time objectives, system flexibility, and system costs must all be balanced to achieve an optimum system design. Considering these issues independently will result in unwanted and/or unexpected system performance tradeoffs. This paper examines these issues in some detail and suggests a system design approach which balances microwave performance and measurement speed with system cost.
J. Saget (Dassault Electronique),J. Garat (CEA/CESTA), November 1990
Radar cross section (RCS) measurements were performed in the 0.1-1 GHz band in an anechoic chamber optimized for microwave frequencies.
Selection of proper instrumentation, antennas, measurement techniques and processing software are discussed.
Experimental results, showing the accuracy and sensibility of the system are presented.
J. Tuovinen (Helsinki University of Technology),A. Lehto (Helsinki University of Technology)
A. Raisanen (Helsinki University of Technology), November 1990
A novel differential phase measurement method is developed. No flexible cables or rotary joints are needed in this method. Phase center positions and phase patterns of two corrugated horns are measured at 105-115 GHz and 176-190 GHz by using this method. Good agreement between the measured values and theoretical values, calculated with the modal matching technique, is obtained. Also a new phase error correction method is introduced. This method makes possible to measure the phase error in the cable and then to remove the error numerically from the results. The accuracy of the phase error correction is limited by the phase measurement device in the system. Experimentally this method is verified at 10 GHz.
W.D. Sherman (Boeing Defense and Space Group),C.R. Pond (Boeing Defense and Space Group),
M.D. Voth (Boeing Defense and Space Group),
P.D. Texeira (Boeing Defense and Space Group), November 1990
A laser tracker using a computer controlled feedback loop has been designed and tested. The tracker follows a small retroreflector embedded in a radar calibration sphere. Angle encoders coupled to two orthogonal scanning mirrors give azimuth and elevation pointing angles to the target. Phase measurements of an intensity modulated laser beam give change in distance to the target, while absolute range is determined by knowing the initial 2p ambiguity interval of the target position. The crossrange accuracy of the system is limited by the scanning mirror encoders to =.063 inches rms at 105 feet (50 microradians). The downrange accuracy of the system is ˜.015 inches rms. This versatile system can be used for: a) contour measurements of models with the aid of a retroreflector moving over the surface, b) accurate determination of the coordinates of a single moving target, and c) determination of the orientation of a large extended target. Anticipated modifications of the system, with their potential precision measurement capabilities and applications, are discussed.
A.R. Lamb (Hughes Aircraft Company),H. Hgai (Hughes Aircraft Company),
J. Paul (Hughes Aircraft Company),
Y. Chu (Hughes Aircraft Company), November 1990
Comparative measurements have been made in a compact range to determine the performance improvements that can be achieved when adding a hardware gate to a CW-based measurement system. Starting with conventional stepped frequency CW measurements made in the time domain mode, high resolution downrange data was collected to determine the background levels of the compact range. This was followed by comparative measurements under the same conditions adding a narrow pulsed hardware gate to reject inter-horn coupling and high returns from the compact reflector. A second mode of comparison was examined by collecting aspect data with a specific range gate fixed about the target. Software gated measurements required more points to insure alias free operation, while the hardware gated measurements allowed fewer points which reduced measurement time without sacrificing any accuracy. Finally, imaging measurements were made with both software and hardware gating to compare the measurement time and accuracy
J. Allison (Hughes Aircraft Company),J. Paul (Hughes Aircraft Company),
R. Santos (Hughes Aircraft Company), November 1990
Pulse-to-pulse amplitude and phase noise can affect the overall measurement accuracy of RCS instrumentation radars. Depending upon the measurement requirements, such noise can limit the overall performance whenever pulse-to-pulse repeatability is required in the signal processing. Radar systems using pulsed TWTAs are subject to high noise due to limitations in the performance of the TWTA modulators and power supplies. A characterization of this additive noise is important to understand the limitations in system performance. Measurements have been made on kilowatt power TWTAs at L and X band as well as 20 watt pulsed TWTAs at S, C, and X/Ku band at various duty cycles and PRFs.
J. Boyles (Hewlett-Packard Company), November 1990
The task of making accurate antenna measurements is complicated by the numerous sources of measurement error in the antenna test range. In addition to the test system performance, the overall measurement uncertainty depends strongly upon the range configuration and user-selected operating conditions. A correct understanding of these systematic and random error sources can help optimize the test range, instrument configuration, and measurement technique to achieve the highest levels of measurement accuracy.
This paper describes dominant error sources present on an antenna test range and gives methods for quantifying their effects on measurement accuracy.
O. Porath (Orbit Advanced Technologies, Ltd.),I. Koffman (Orbit Advanced Technologies, Ltd.),
N. Isman (Orbit Advanced Technologies, Ltd.),
Y. Rosner (Orbit Advanced Technologies, Ltd.), November 1990
This paper describes an automated radome test and evaluation system, which quickly and accurately measures the electrical boresight shift and loss caused by the presence of a radome in front of a monopulse antenna. The system was required to measure the boresight deflection through all 60 spatial relative angles between the antenna and the radome. The conventional methods of radome characterization were useless for this range of relative angles (mechanically impossible).
To overcome this problem, a unique dynamic tracking method was developed. In this methos, the antenna is mounted on a dual-axis gimbal attached to the radome. The gimbal by itself is mounted on a second dual-axis positioner. The antenna gimbal scans the radome through all the required relative angles, while the monopulse error is continuously measured and used to control the radome positioner, in order to return the antenna to the boresight position. The readings of the angles and the values of the monopulse error establish the boresight deflection results, which are highly accurate because the apparent (deflected) source is accurately tracked, and the antenna is boresighted to it. The system measures all the 60 angles in 70 minutes time, at an accuracy of 0.3mRAD.
V. Autry (Hewlett-Packard Company),B. Coomes (Hewlett-Packard Company), November 1990
This paper examines antenna pattern measurements of RF frequency antennas (300 kHz-3 GHs) using an integrated source/receiver and measurement control software. Current microwave measurement systems provide sufficient measurement capability but are often too expensive to be used on ranges which require test frequencies of less than 3 GHz such as aircraft communications, cellular radio, GPS, and satellite telemetry antenna. Several system block diagrams based on the HP 8753 network analyzer will be examined with respect to system performance, measurement accuracy, and cost. System considerations for outdoor RF ranges such as RFI susceptibility will also be addressed.
M.J. Brenner (ESSCO),D.O. Dusenberry (Simpson, Gumpertz & Heger Inc.),
J. Antebi (Simpson, Gumpertz & Heger Inc.), November 1990
A 75 foot diameter offset paraboloidal outdoor compact range reflector was designed for operation up to 95 GHz and installed at Ft. Huachuca, Arizona. The need for high frequency operation required that a highly accurate reflector surface be maintained in the desert’s harsh thermal and wind environment. The use of thermal modeling to predict the temperature distribution in the structure, along with extensive finite element analysis to determine the structure’s distortions from thermal, wind and gravity loads were integral to the reflector design. Using the above tools, thermal isolation techniques were developed to minimize the harmful effects of the thermal environment on surface accuracy.
A surface error budget based upon both calculations and measurements shows an overall rms error of 4.9 mils under optimal environmental conditions, degrading to only 6. Mils under the worst operating conditions.
E. Hart (Scientific-Atlanta, Inc.),W.G. Luehrs (Scientific-Atlanta, Inc.), November 1990
A major objective in the design of an RCS measurement facility is to obtain the greatest possible productivity (overall measurement efficiency) while maintaining the accuracy and sensitivity necessary for low radar cross section targets. This paper will present parameters affecting the total throughput rates of an indoor facility including instrumentation, target handling, and band changes-one of the most time consuming activities in the measurement process. Sensitivity and accuracy issues to be discussed include radar capabilities, feeds and feed clustering, compact range, background levels, and diffraction control.
J. Guerrieri (National Institute of Standards and Technology),S. Canales (National Institute of Standards and Technology), November 1990
Antenna engineers recognize that the planar near-field method for calibrating antennas provide accurate pattern and gain measurements. Bothe the pattern and gain measurements require some degree of probe position accuracy in order to achieve accurate results. This degree of accuracy increases for antennas that have structured near-field patterns. These are antennas in which the amplitude and phase change rapidly over a very small position change in the near-field scan plane.
The National Institute of Standards and Technology (NIST) has recently measured an antenna with a very structured near-field pattern. This measurement was performed using a new probe positioning system developed at NIST. This measurement will be discussed and results will be presented showing how slight probe position errors alter the antenna pattern and gain.
This site uses cookies to recognize members so as to provide the benefits of membership. We may also use cookies to understand in general how people use and visit this site. Please indicate your acceptance to the right. To learn more, click here.
