AMTA Paper Archive


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AMTA Paper Archive

Characterization of antennas for RCS measurements
S. Kashyap (National Research Council, Ottawa),S. Mishra (National Research Council, Canada), November 1986

This paper reviews procedures and techniques employed for calibrating antennas used in electromagnetic compatibility (EMC) measurements. Details of our measurement procedure and results using the TEM cell and the three antenna methods are described.

Measured blockage of a parabolic antenna by a tall vertical obstruction
D. Sirmans (National Severe Storms Laboratory), November 1986

It is sometimes necessary to tolerate a narrow vertical obstacle in proximity to an antenna system. This study quantifies the effects on the antenna horizontal pattern of an obstruction with vertical dimension large compared to the antenna and horizontal dimension small compared to the antenna. Both dimensions are large compared to wavelength.

Measurement of doubly curved reflector antennas
S.H. Lim (Andrew Antenna Company Ltd.),R. Boyko (Andrew Antenna Company Ltd.), November 1986

This paper describes the mechanical as well as electrical measurement of doubly curved reflector antennas. The techniques developed for measurement of the new Canadian RAMP Primary Surveillance Radar antenna are described. Instead of a conventional full size template fixture to measure the antenna contour accuracy, an optical twin-theodolite method is used. The problems of the method are discussed and a new simplified analysis for calculating reflector error of doubly curved antennas is presented. Reflector errors are calculated and displayed concurrent with the actual measurements. The measurement of primary and secondary patterns for such antennas are described. Included are brief descriptions of the improved Andrew pattern test range and anechoic chamber facilities.

Design and construction of an UHF passive intermodulation set to meet M-SAT requirements
J.G. DuMoulin (David Florida Laboratory),F. Buckles (David Florida Laboratory), H. Raine (David Florida Laboratory), P. Charron (David Florida Laboratory), November 1986

Intermodulation products are generated when multiple frequency signals are applied to a circuit element having a non-linear input/output characteristic. The space community first became aware of the Passive Intermodulation (PIM) problem due to the difficulties encountered by the Fleetsatcom program. This paper describes the design philosophy and construction of an "UHF Test Set" to satisfy the test requirements of the M-Sat program. Predicted response curves of the IM characteristics of HPA's, ferrite isolator and passive hardware are presented as tools for the filter designer interested in the test set design, with the required rejection values for the various filters to be used.

Simulation of an aircraft flying through a ground station to satellite link
W.D. Burnside (The Ohio State University ElectroScience Laboratory),A. Dominek (The Ohio State University ElectroScience Laboratory), M. Gilreath (NASA/Langley Research Center), R.C. Rudduck (The Ohio State University ElectroScience Laboratory), T-H. Lee (The Ohio State University ElectroScience Laboratory), November 1986

The potential for an aircraft to fly directly through a ground station-to-satellite link becomes more significant if the link is located closer to an airport, obviously. Because this situation is much more likely near airports, it is appropriate to examine the effects of such an encounter.

Holographic antenna measurements using a single receiver
T.H. Legg (National Research Council, Ottawa), November 1986

Holography measurements (see for example Bennet et al., 1976 and Scott and Ryle, 1977) have recently been made in which it was possible to use a single receiver and no correlator. The object was to measure the deformation with changing elevation angle of the 46m radio telescope at the Algonquin Radio Observatory, Lake Traverse, Ontario. To allow measurements over a wide range of elevation angle, the emission from natural water-line (22.235 GHz) masers was chosen as a source of signal.

The Enhanced capabilities and computer interfaces of the antenna analyzer systems at RCA Astro-Electronics
M. Cuchanski (RCA/Astro Electronics),C. Renton (RCA/Astro Electronics), D. Wozniak (RCA/Astro Electronics), November 1986

This paper describes the computer system interfaces and hardware additions which provide engineers enhanced capabilities and greater flexibility from their antenna measurement systems. RCA Astro-Electronics has built three outdoor antenna ranges, each equipped with Scientific-Atlanta Antenna Analyzers. Two Series 2020 and one Series 2080 Analyzer are used to perform data acquisition and preliminary data processing for the three antenna ranges. Both S-A 2020 system computers have direct interface capabilities with two remote computer systems, which are primarily used for antenna design and analysis. The S-A 2080 system is interfaced indirectly, via one of the S-A 2020 range computers. Direct line and modem interfaces provide user access to remote computer software and allow up and downloading of measured or computed data files. Using RCA software resident in each range computer, measured data files are unpacked, reformatted and downloaded for off-line processing. This process accelerates test schedules and allows analysis software to process data files from three antenna ranges in a single data format. Other enhanced system features include access to remote analysis software, requiring large disc storage space, for real-time evaluation at the antenna analyzer location.

Conformal test coupler for measurements through antennas mounted on fuselages
A.D. Ergene (General Dynamics Convair Division), November 1986

Theory, design, and test results of a conformal test coupler that can be mounted on the exterior of a vehicle for direct on site measurements of a fuselage mounted L-band antenna are presented. When there is a requirement to test vehicle instrumentation for radiated power, signal format, etc., a desired method is to couple the test equipment directly to the dedicated antenna on the vehicle. Cavity test couplers have been traditionally employed for direct measurements at the antenna under test. However, a low-profile conformal cavity has poor performance when there is no match between the energy radiated by the antenna and the received energy in the cavity. To suppress unwanted resonances and a high Standing Wave Ratio, such mismatched cavities are loaded heavily with absorber material inside, and in operation exhibit high sensitivity to surface contact and high insertion loss, yielding nonrepeatable measurements. The coupler presented here is a nonresonant cavity that supports a TEM mode compatible with the radiation from the vehicle antenna and avoids spurious resonance spikes. It exhibits extremely low insertion loss and is not sensitive to mounting misalignment. A circumferential microstrip radiator with multiple feed points and a matching network on the back side of the same substrate is wrapped around the inside of a top-hat cylindrical aluminum container. The particular test cavity was designed for the vertically polarized L-band IFF antenna on the cruise missile; however, the same principle makes testing of other fuselage-mounted antennas easier and more reliable.

Performance of an optimum antenna range illuminating horn
J. Russum (Texas Instruments Inc.), November 1986

The paper describes a simple feed horn designed to illuminate an antenna test range used to measure broad bandwidth antenna patterns with rotating linear polarization. Principal requirements of the feed are equal E and H plane beamwidths with minimal sidelobes in all planes. These characteristics are required to avoid undesirable pattern modulation caused by varying specular scatter and unequal beamwidth vs rotation angle. A survey of pyramidal, conical, and diagonal feed horn patterns revealed that each configuration has high sidelobes in at least one plane making it undesirable for the intended application. Both the pyramidal and conical horns have high side lobes in the E plane. The diagonal horn has very good sidelobe characteristics in the principal planes, but has 13 to 16 dB sidelobes in the diagonal plane.

Measurement of element pattern and its usage in the development of multi-beam arrays
P. Kirshner (ELTA Electronic Industries),I. Oz (ELTA Electronic Industries), November 1986

Electronic scanning phased arrays are being used more and more in radar, EW and communication systems. The development of such an array can be divided into two separate parts: development of the radiating elements and development of the beam forming network. The development of these two parts is often done in parallel and the radiating elements should always be developed taking into consideration the whole array and not only single elements.

Displaced phase center antenna measurements for space based radar applications
H.M. Aumann (Massachusetts Institute of Technology),A.J. Fenn (Massachusetts Institute of Technology), F.G. Willwerth (Massachusetts Institute of Technology), November 1986

An investigation of the use of array mutual coupling measurements, to evaluate displaced phase center antenna (DPCA) performance, is made. The details of a subscale space based radar (SBR) DPCA phased array and the array mutual coupling technique are discussed. DPCA results are quantified experimentally under a number of test conditions. It is shown that the test array beam decorrelation computed from array mutual coupling data, is in good agreement with both theoretical predictions, planar near field measurements and direct far field measurements.

Troubleshooting test facilities with a high resolution instrumentation radar
T.J. Lyon (The Howland Company, Inc.),A.R. Howland (The Howland Company, Inc.), November 1986

This paper presents data from facility evaluation tasks on current projects. The data were obtained on outdoor free-space pattern test facilities, and in anechoic chamber RCS test facilities.

Broadband reflectivity and scatter evaluation of RF absorbers
A.R. Howland (The Howland Company, Inc.),T.J. Lyon (The Howland Company, Inc.), November 1986

This paper describes specially constructed instrumentation and positioning systems used in evaluating RF absorber, discusses measurement techniques, and presents data and conclusions from current programs. The selected absorbers which were evaluated are typical of those used in anechoic chambers and terminated ranges for antenna, radome and RCS testing.

Evaluation of rain erosion materials for aircraft antenna-radomes
T.A. Gilligo (Naval Air Development Center), November 1986

For many years, rain impact and erosion failures to aircraft radomes have been a recurring problem. Impingement upon rain droplets by aircraft traveling at velocities of 300 mph, or greater, may be destructful to radomes and jeopardize the function of associated antennas, unless sufficient rain erosion resistant materials are employed in the construction. Changes to the surface of a radome due to rain erosion, such as porosity and structural failure, will affect electrical performance. Other material properties that must be considered besides rain erosion are dielectric constant and lost tangent.

Problems associated with antenna measurements in G-band (140-220 GHz)
D.A. Lord (Aerojet ElectroSystems), November 1986

Aerojet ElectroSystems of Azusa, California, has a commitment to design and test antenna systems in the 149-184 GHz frequency range. Many problems have arisen in attempting to design and implement a feasible system to make antenna measurements. This paper will discuss the problems that have been encountered, the solutions that have been implemented, and future considerations. Topics discussed will include availability of equipment, source stabilization, signal detection, and range design considerations.

On site measurement of antenna impedance, current and voltage at H
W.V. F. Tilston (Til-Tek Limited ),G. Suggitt (Til-Tek Limited ), T. Tralman (Til-Tek Limited ), November 1986

It is often desirable to measure antenna impedance during an operational state. In applications such as experimental studies of ionospheric properties it is desirable to determine the instantaneous impedance. Most applications will involve adaptive tuning such as in antenna filter or multicoupler systems to maintain resonance despite other operations being conducted on the system. Adaptive tuning of HF whip antennas will provide compensation for environmental conditions such as ice load, or proximity to various objects. In cases where the antenna, or its surrounding, is affected by the power level, it is also desirable to measure the impedance over the power range as well as frequency. Two methods of determining impedances will be discussed in this paper. The first method is that of voltage and current probes and the second that of directional couplers for measuring forward and reflected waves.

The Coefficient file: a basic feature of spherical near-field software architecture
D.W. Hess (Scientific-Atlanta Inc.), November 1985

The matrix of scattering coefficients which describes the transfer of excitation between the port of an antenna and free space forms a fundamental description of that antenna. In carrying out the spherical near-field to far-field transforms for a probe-corrected measurement one is required to utilize the scattering coefficients of the probe antenna. An essential feature of any software system which supports probe-corrected measurements is the capability of analyzing and storing these coefficients.

Sample spacing requirements for spherical surface near-field measurements
E.B. Joy (Georgia Institute of Technology),J.B., Jr. Rowland (Georgia Institute of Technology), November 1985

This paper presents results of an on-going research program at Georgia Tech into the theory and technique of antenna measurements. Specifically this paper presents the results of an investigation into sampling requirements for electromagnetic measurements performed on a surface enclosing an antenna under test (AUT).

Near field range facility design
D. Slater (Antenna Systems Laboratory), November 1985

Lessons learned in the design of large, planar near field ranges used at millimeter wavelengths are described. Specific issues include facility design, RF equipment, scanner design, dynamic position measurement, servo control and software requirements.

An Outdoor UHF cylindrical surface near-field range
K.W. Cozad (Harris Corporation),E.B. Joy (Georgia Institute of Technology), November 1985

This paper describes the Harris Corporation, Broadcast Group, Outdoor, Cylindrical, Near-Field Antenna Range. The range is located on a bluff overlooking the Mississippi River flood plain near Quincy. IL and is used for the alignment and testing of UHF-TV transmitting antennas.







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