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RF marking principle and its application in making antenna measurements
P.K. Wahi,Y. Boison, November 1993
The antenna analyzer is specifically designed to make use of measurement techniques that have been difficult to use until now The analyzer is an original vectorial receiver design, based upon the analysis of one of the sidebands of the marked RF measurement signal. Thanks to the RF marking process, the antenna analyzer is not the only equipment that allows characterization (in amplitude, phase or return loss) of all devices in a transmitting chain, including the high power elements, without cutting off the transmission. Originally introduced for the analysis of wired antennas in UHF-VHF bands, its use is now extended to microwave antenna measurements, especially printed circuit antennas. A special characteristic of the new analyzer, ESTAR 2110 is its capacity to measure the phase of RF signal with power levels as low as -120dBm. The analyzer is ideal for elaborate analysis of fundamental antenna parameters such as RF current distribution, close field, antenna pattern, impedance and phase balance of antenna network. The paper describes the marking principle and its use in making antenna parameter measurements.
Effect of spherical measurement surface size on the accuracy of test zone field predictions, The
D.N. Black,E.B. Joy, J.W. Epple, M.G. Guler, R.E. Wilson, November 1993
The field present in the test zone of an antenna measurement range can be calculated from the range field measured on a spherical surface containing the test zone. Calculated test zone fields are accurate only within a spherical volume concentric to the measurement surface. This paper presents a technique for determining the probing radius necessary to create a volume of accuracy containing the test zone of the range. The volume of accuracy radium limit is caused by the spherical mode filtering property of the displaced probe. This property is demonstrated in the paper using measured field data for probes of differing displacement radii. This property is used to determine the volume of accuracy radium from the probing radius. This is demonstrated using measured far-field range data.
Simulation and verification of an anechoic chamber
R.M. Taylor,E.S. Gillespie, S.R. Renegarajan, November 1993
This paper considers an electromagnetic field simulation of an anechoic chamber with experimental verification. The simulation is a Geometric Optics (Ray Tracing) mathematical model of the direct path between two antennas and interfering scattering. There are two separate models due to the frequency dependent nature of the pyramidal radar absorbing material (RAM). The model for the frequency range of 30 to 500 MHz was used to characterize the specular scattering. The specular scattering was modeled as a lossy, tapered, TEM transmission line in an inhomogeneous anisotropic tensor material. The frequency range from 500 MHz to 18 GHz was characterized by dominant tip diffraction of RAM patches and the model made use of a Uniform Theory of Diffraction code for a dielectric corner. The measurements and simulations were based on an azimuthal cylindrical scan. Diagnostic measurements were also performed by a cylindrical scan of a directional horn antenna to locate scattering sources in the chamber. A cylindrical wave, modal expansion of the diagnostic data which included a one dimensional Fast Fourier Transform with Hankel function expansions.
Ground and airborne calibration of the ground to air imaging radar
W. Nagy,E.L. Johansen, November 1993
A Ground to Air Imaging Radar system (GAIR) used to perform diagnostic imaging and total RCS measurements on low observable airborne targets has been developed by the Environmental Research Institute of Michigan (ERIM). In order to ensure accurate measurement of the scatterers contributing to a target's radar signature, proper calibration in imperative. The use of external calibrators to measure the end-to-end system transfer function is the ideal way to perform a system calibration. However, this is a more difficult and challenging task with a ground based radar viewing an airborne target, as opposed to a traditional airborne SAR which views an array of ground based trihedral corner reflectors. This paper will discuss the internal and external calibration methods used in performing an end-to-end system calibration of the GAIR. Primary emphasis is placed upon the external calibration of the GAIR and the three independent measurements utilized: a ground based corner reflector, a sphere drop, and an in-scene calibrator. The system calibration results demonstrate that the GAIR is an accurately calibrated radar system capable of providing calibrated images and total RCS data. Moreover, only the ground and internal measurements are required on a daily basis in order to maintain system calibration
Experimental range facility for RCS measurement and imaging research
J. Burns,D., Jr. Kletzli, G. Fliss, November 1993
A small compact range measurement facility has been installed at the Environmental Research Institute of Michigan (ERIM) for research aimed at improving RCS measurement and radar imaging techniques. This paper describes the facility, which is referred to as the Experimental Range Facility (ERF). The ERF has two instrumentation radars; a Flam & Russell FR959 gated CW radar and a Hughes MMS-300 pulsed radar. The radars are connected to a suite of workstations, which support a variety of internally and externally developed radar imaging and data exploitation software. The ERF is also equipped with sophisticated target positioning control and sensing equipment.
Radar target measurements in multipath environment
Y.J. Stoyanov,M.A. Sekellick, W.H. Schuette, Y.J. Stoyanov, November 1993
The presence of the sea surface has a powerful influence on the scattering characteristics of marine targets during radar cross section (RCS) measurements. To obtain accurate RCS measurements of a large, distributed marine target, the radar site must satisfy various requirements. The major requirement is to provide quality RCS data without strong multipath distortion of the target return signal. In this paper multipath effects on a large scatterer measured at both low-and high-elevation radar sites are summarized. It is observed that multipath effects contribute strongly to the RCS of the target measured at a low elevation radar site. The data show large RCS fluctuations of more than 15 dB when a scatterer is measured at difference altitudes or ranges. The quality of the data measured at a low-elevation radar site then becomes questionable, which creates difficulties in assessing the true RCS of the target. For diagnostic purposes, it may be necessary to change the target range or altitude several times to make a credible assessment of RCS. The same target measured at a high-elevation site has less multipath influence on the RCS data, making assessment of the true RCS feasible.
Characterization of aeronautical antennas for INMARSAT communication
S. Mishra,J. Moraces, J. Smithson, J.G. Dumoulin, P. Charron, November 1993
Aeronautical SATCOM systems for INMARSAT typically employ circular polarized electronically or mechanically steered multi beam antennas. Characterization of thee antennas requires extensive measurements that differ from conventional antenna pattern measurements. Some of these are: A. Multiple frequently CP gain, axial ratio, and discrimination measurements over a hemisphere for a large number of beams. B. Noise temperature and G/T measurements C. Carrier to multipath rejection D. Intermodulation characteristics E. Receiver and Transmitter system characteristics Details of instrumentation and procedure for these tests are presented with special emphasis on issues such as measurement speed, accuracy and processing of large amounts of data.
Improved NRL arch technique for broad-band absorber performance evaluations
K. Liu,J. Wineman, J.M. Kilpela, November 1993
In this paper, a new error correction technique is introduced to improve the accuracy and efficiency of the traditional NRL Arch method. The use of this integrated technique allows one to correct the error terms in the traditional NRL arch setup so that a broadband evaluation of the performance of the absorber product can be performed with much better accuracy and efficiency. This technique also allows one to conduct large bistatic angle evaluation of absorbers without the cross talk and other error signal interferences. Design guidelines for a broadband NRL test arch are provided so as to successfully implement this improved NRL Arch method for a broadband evaluations of anechoic absorbers. Sample test results from Ray Proof's broadband test arch (0.5-6 GHz) are also presented.
Transverse pattern comparison method for characterizing antenna and RCS compact ranges, The
S. Brumley, November 1993
This paper briefly reviews existing compact range performance characterization methods showing the limitations of each technique and the need for an accepted and well understood technique which provides efficient and accurate characterization of compact range measurement accuracy. A technique known as the transverse pattern comparison method is then described which has been practiced by the author and some range users for the past several years. The method is related to the well known longitudinal pattern comparison method, however, comparisons are conducted in the transverse planes where the required span of aperture displacement is much smaller and does not exceed the dimensions of the quiet zone. This method provides several advantages for characterizing compact range performance as well as enables range users to improve achievable measurement accuracies by eliminating the impact of extraneous signal errors in the quiet zone.
Effect of spherical measurement surface size on the accuracy of test zone field predictions, The
D.N. Black,E.B. Joy, J.W. Epple, M.G. Guler, R.E. Wilson, November 1993
The field present in the test zone of an antenna measurement range can be calculated from the range field measured on a spherical surface containing the test zone. Calculated test zone fields are accurate only within a spherical volume concentric to the measurement surface. This paper presents a technique for determining the probing radius necessary to create a volume of accuracy containing the test zone of the range. The volume of accuracy radium limit is caused by the spherical mode filtering property of the displaced probe. This property is demonstrated in the paper using measured field data for probes of differing displacement radii. This property is used to determine the volume of accuracy radium from the probing radius. This is demonstrated using measured far-field range data.
HARC/STAR Microwave Measurement Facility: physical description and capabilities, The
B.D. Jersey,A.J. Blanchard, B.A. Williams, B.D. Krenek, W.N. Colquitt, November 1993
A complete description is given of the unique radar cross-section (RCS) measurement facility built at the Houston Advanced Research Center in The Woodlands, TX. The uniqueness of this chamber comes from its ability to independently move the transmit and receive antennas, which can each be moved to any position within their respective ranges of motion to a resolution of about 0.05 degrees. The transmit antenna is fixed in azimuth, but can be moved in elevation: the receive antenna is free to move in both azimuth and elevation. Additionally, the target can be rotated in azimuth by means of an azimuth positioner. Analysis has been performed to determine the impact of chamber effects on measurement accuracy. The most notable chamber effect comes from the two large aluminum truss structures, which are the mounting supports for the transmit and receive antennas. Fortunately, the scattering from these structures can be readily separated from the desired target return through the use of range (time) gating. Time domain results are presented showing the effects of these structures.
HARC/STAR Microwave Measurement Facility: measurement and calibration results, The
B.D. Jersak,A.J. Blanchard, J.W. Bredow, November 1993
Numerous monostatic radar cross-section (RCS) calibration routines exist in the literature. Many of these routines have been implemented at the RCS measurement facility built at the Houston Advanced Research Center in The Woodlands, TX. Key monostatic results are presented to give an indication of the measurement accuracy achievable with this chamber. Unfortunately, bistatic calibration routines are not nearly as common in the literature. As with the monostatic routines, a number of bistatic routines have been implemented and typical results are presented. Additionally, descriptions are given for some of the reference targets along with their support structures that are used during calibration.
Spherical nearfield measurement of a large deployable multibeam satellite antenna
T. Beez,J. Schneemann, November 1993
A large deployable multibeam antenna for communication satellites operating in the Ka band with 2.5 GHz transmit/receive bandwidth was developed and measured. The antenna is an offset Cassegain system with a 4.7 m diameter mail reflector divided into a central and 24 rigid deployable panels. One application studied in detail was the continuous illumination of the FRG with 16 beams. Spherical nearfield measurement techniques were used to validate the predicted performance. Because the gravity influence would cause inadmissible deformations, a compensation device must be used. To take into account the influence of the remaining deformations varying with the elevation position of the antenna, a special analysis software was developed which uses measured surface coordinates. Because measured and computed values agree well, it is possible to predict the performance in orbit precisely. A pointing accuracy of 0.01 degrees was achieved by adjustment of the sub reflector using a monopulse tracking system.
New extrapolation algorithm for high resolution imaging applications
M.R. van de Goot,A.G.H. Gerrits, V.J. Vokurka, November 1993
In ISAR applications data is acquired on a circular grid. In further processing, data on a rectangular grid is obtained by interpolation. This causes the loss of data outside the interpolated area. The latter can be corrected by extrapolation, but this can give incorrect information. A new technique s proposed which uses a larger rectangular area than in the above mentioned case. Some parts of this rectangle are calculated by extrapolation. Because most of the data in the larger rectangular area consists of original data, only minor parts are extrapolated. Consequently, this method is expected to be more reliable than traditional extrapolation techniques. Simulations have shown that the data obtained by the new interpolation - extrapolation scheme provide a considerable improvement to the amplitude - and phase accuracy across the enlarged rectangular grid.
RCS target non-contact position measurements
N. Panich,A. Trabelsi, I. Bryskin, M. Levin, M. Segal, M. Winebrand, November 1993
ORBIT's String Reel Target Manipulation System is used to support and rotate a target during RCS measurements. One of the challenges in this kind of RCS measurement is to accurately determine the position of the target in space, since the weight and moment of inertia of the target and the string flexibility do not allow measuring its position with conventional methods (linear encoder, etc.). In order to overcome this problem, the Non-Contact Optical Measurement System (NCOMS) has been developed and tested at ORBIT. The system provides the capability for precision tracking of the target position (X, Y, Z) and orientation (ROLL, PITCH, YAW). NCOMS is a computer-controlled system and operates by using two standard CCD cameras (stereo technique), as well as by use of a single camera with insignificant accuracy degradation. Another advantage of NCOMS is that the system operation does not require accurate camera positioning. The only requirements for CCD camera installation are target visibility and use convenience.
Novel APC-methods for accurate pattern determination
J. van Norel,V.J. Vokurka, November 1993
Antenna pattern measurements are dominantly influenced by the presence of extraneous fields in the test zone. A fast and simple way to recognize problems in pattern measurements provides the Antenna Pattern Comparison-technique (APC). This method usually consists of recording azimuthal patterns on different positions across the test zone. Differences in the amplitude data give a rough indication for the magnitude of the interfering signal. The "Novel APC-method" (NAPC) employs both amplitude- and phase-data so that it becomes possible to separate the direct and the extraneous signals from each other. It will be shown that this method is eminently suited to correct radiation patterns of high-gain and low-sidelobe antennas. For verification purposes corrected patterns are compared with time-dated ones and the resemblance is excellent. It is concluded that the NAPC-method is promising and powerful technique for accurate antenna pattern determination, mainly because it can be easily implemented for most applications.
Hughes Aircraft Company RCS/antenna measurement chamber characterization
A. Jain,C.R. Boerman, E. Walton, V.J. Vokurka, November 1993
The Hughes Aircraft Company Compact Range facility for antenna and RCS measurements, scheduled for completion in 1993, is described. The facility features two compact ranges. Chamber 1 was designed for a 4 to 6 foot quiet zone, and Chamber 2 was designed for a 10 to 14 foot quiet zone. Each chamber is TEMPEST shielded with 1/4 inch welded steel panels to meet NSA standard 65-6 for RF isolation greater than 100 dB up to 100 GHz, with personnel access through double inter locked Huntley RFI/EMI sliding pneumatic doors certified to maintain 100 dB isolation. While Chamber 1 is designed to operate in the frequency range from 2 to 100 GHz, Chamber 2 is designed for the 1 to 100 GHz region. Both RCS measurements and antenna field patterns/gain measurements can be made in each chamber. The reflectors used are the March Microwave Dual Parabolic Cylindrical Reflector System with the sub-reflector mounted on the ceiling to permit horizontal target cuts to be measured in the symmetrical plane of the reflector system.
Modeling System Reflections To Quantify RCS Measurement Errors
Azar S. Ali, November 1993
RCS measurement accuracy is degraded by reflections occurring between the feed antenna, the range, and the radar subsystem. These reflections produce errors which appear in the image domain (both 1-D and 2-D). The errors are proportional to the RCS magnitude of the target under test and they are present in each of the typical range calibration measurements. Current 2-term error models do not predict or account for the above errors. An improved 8-term error model is developed to do so. The model is based on measurable reflections and losses within the range, the feed antenna, and the radar. By combining the improved error model with the commonly used 2-term RCS range calibration equation, we are able to quantify the residual RCS errors. The improved error model is validated with measured results on a direct illumination range and is used to develop specific techniques which can improve RCS measurement accuracy.
550 GHz near-field antenna measurement system for the NASA sub-millimeter wave astronomy satellite, A
D. Slater, November 1994
This paper describes a 550 GHz planar near-field measurement system developed for flight qualification of the radio telescope carried onboard the NASA submillimeter wave astronomy satellite (SWAS). The very high operating frequency required a new look at many near-field measurement issues. For example, the short wavelength mandated a very high precision scanner mechanism with the accuracy of a few microns. A new thermal compensation technique was developed to minimize errors caused by thermally induced motion between the scanner and spacecraft antenna.
Probe compensation characterization and error analysis in cylindrical near-field scanning
Z.A. Hussein, November 1994
A novel computer simulation methodology to properly characterize the role of probe directivity/pattern compensation in cylindrical nearĀ­ field scanning geometry is presented. The methodology is applied to a linear test array antenna and the JPIJNASA scatterometer (NSCA1) radar antenna. In addition, error analysis techniques of computer simulation and measured have been developed to determine the achievable accuracy in pattern measurements of the NSCAT antenna in cylindrical near field.

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