AMTA Paper Archive
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An Airborne S-band telemetry antenna system which uses a Luneberg lens aperture
An S-band telemetry antenna system was designed and fabricated using a 30-inch diameter lightweight Luneberg lens as the aperture. It is equipped with four feeds in the azimuth plane to achieve single beam patterns or multiple beam patterns. Initial measurements with the lens without a radome were made with various feeds and feed combinations in the compact range of the Georgia Tech Engineering Experiment Station. The final design also done by Georgia Tech to Kentron Specifications, uses a custom designed quad ridged circular feed with orthogonal linear polarization outputs which are converted to left- and right-hand circular polarization using 90o hybrid couplers. A control panel permits the operator to manually select a single beam coverage of 11o x 11o, twobeams combined for 22o x 11o sector coverage, or four beams combined for 44o azimuth x 11o elevation sector coverage. A automatic mode permits the full gain of a single beam, about 22 dB, to be attained and switched automatically to the RF feed containing the greatest signal power as sensed by eight total power radiometer receivers; one for each orthogonal polarization for each of the four antenna feeds. Selectable integration time constants are 0.1, 1, 10, and 100 milliseconds. Dependable switching is obtained for signals of -99 dBm or greater. The RF switching is achieved by PIN-diode switches in 10 nanoseconds. The system employs eight state-of-the-art gain and phase matches GaAs FET low-noise preamps which have a noise figure of 1.1 dB and gain of 51 dB. External limiters at the input of each LNA protect the devices from accidental RF inputs up to six watts average power. The system was designed as a removable package to be flown aboard the U.S. Army’s C-7A Caribou aircraft with an opened rear cargo ramp to collect terminal TM data from missile reentry vehicles (RV’s) impacting near the Kwajalein Missile Range. Flight testing of the system against target of opportunity missions began the third week of June 1982. The system is expected to be declared an operational system in support of ballistic missile testing by December 1982.
A Simplified technique for probe position error compensation in planar surface near field measurements
This paper presents the results of research conducted to compensate near field measurements for known errors in near field probe position. The complete solution for probe position error compensation and associated computer algorithm developed by Corey as a Ph.D. dissertation resulted in a large computer memory and computation time requirements. Corey’s results showed, however, that the prime effect of probe positioning error was a change in the near field measurement phase in the direction of main beam propagation. It was also shown that the sinusoidal components of the probe position error produced spurious sideband propagation directions in the calculated far field patterns. This information has been used to develop a simplified probe position error compensation technique which requires negligible computer storage and computation time. An early version of this technique has recently been implemented at RCA for the Aegis near field measurement facility. The technique and sample results are presented for a small probe position errors and for a low sidelobe level antenna measurement.
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.
An Antenna pattern arch for measurements over sea water
The Naval Underwater Systems Center has under construction an antenna pattern arch for measuring the radiation pattern of submarine antennas protruding above the sea water surface. The 70-foot radius tripodal arch is constructed of laminated wood members located over a 66-foot by 93-foot concrete pool which will contain a six inch depth of sea water. A well is located off-center in the pool for mounting the antenna under test. Pattern measurements will be made from 20 MHz to 2 GHz and at antenna heights of up to 15-feet above the sea water. Heretofore this over-sea water pattern information has been unobtainable. The important criteria for far-field antenna measurements are mentioned. The Numerical Electromagnetic Code (NEC) was used to model typical submarine antennas at various frequencies in order to predict the accuracy of the arch range. NEC uses moment methods to determine the arch patterns and the far-field patterns.
Automatic gain measurement system
A common method for determining gain on an antenna pattern range is to use the substitution method which involves comparing the response of the test antenna with that of an antenna of known gain. For situations where a standard gain horn is the appropriate reference, this does not present a problem. Calibration curves of these horns are available covering all frequencies for which horns are available, and the horns themselves can be conveniently stored in a cabinet or on a wall rack.
Phased array testing in the compact antenna range
Acceptance testing of the AN/SYR-1 Electronically Steered Phased Array (ESPA) antenna in a Compact Antenna Range is described. Unique to the testing described are (1) generation of the beam steering commands to the phased array as well as control of the positioner and recording equipment by a single desktop computer and (2) the recording of S-band antenna patterns after down-conversion to a 300 MHz IF. Modifications and interfaces to the standard Compact Antenna Range equipment for testing of the multi-element planar phased array are described.
Performance measurements of a low sidelobe adaptive nulling array
We performed several adaptive nulling experiments on a low sidelobe mono-pulse antenna. The test bed antenna was an 80 element linear array that could achieve sidelobe levels of about 35 dB below the peak of the main beam. Some of the experiments included testing gradient search algorithms, partial adaptive nulling, and nulling in sum and difference channels. The adaptive nulling computer programs as well as the antenna control programs were run from a Scientific Atlanta 2020. This paper describes the test set up, the procedures used to measure the far-field patterns, and the adaptive nulling performance of the test bed data.
A Modular antenna analyzer
Recognizing that testing requirements differ, an automated system must be capable of adapting different instrumentation to a specific test. The Series 2080 Modular Antenna Analyzer consists of a computer and processing subsystem (CPS) and four subsystems for antenna measurement applications. The CPS being the nucleus of the Series 2080 system is composed of a computer, appropriate peripherals for interface capability, data storage, data analysis and acquisition software and console. The four subsystems can be comprised of variable instrumentation for a receiving, a positioner control, a signal source and an antenna pattern plotting subsystems. The instrumentation can be supplied by the customer, by Scientific-Atlanta or by other manufacturers.
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.
Design and calibration of a 250 MHz antenna test range at Canada's David Florida Laboratory
This paper deals with the design, calibration and performance of a new antenna test range facility at the David Florida Laboratory in Ottawa, making use of an existing 40 foot cube anechoic chamber and a Scientific-Atlanta 2020 system. The main purpose is to use the same test range for the calibration of a nominal seven foot by five foot Standard Gain Horn and ultimately for gain and pattern testing of an eight foot space qualified axial mode helix, which must be maintained inside the anechoic chamber. This rules out a completely outdoor test range.
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.
G/T measurement of highly directive antenna systems
A technique for improving the accuracy of G/T measurements of highly directive antennas is introduced. The technique presents was developed to overcome uncertainties in ephemeral information, antenna positioning, system gain stability, and other random and nonrandom phenomena. The particular application discussed uses Casseiopeia-A as a noise source but the technique can be adapted for use with other extraterrestrial noise sources.
Design and Calibration of Standard Gain Horns in the 200-400 MHz Range
Paper not available for presentation.
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.
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.
Cylindrical near field test facility for UHF Television Transmitting Antennas
This paper describes a horizontal, cylindrical surface, near-field measurement facility which was designed and constructed in 1984 and is used for the determination of far field patterns from near field measurement of UHF television transmitting antennas. The facility is also used in antenna production as a diagnostic and alignment tool.
The Statistics of measured antenna patterns
The parameters measured on antennas vary from unit-to-unit depending on the manufacturing and test tolerances. It is often useful to be able to predict the statistical distribution expected in production for properties such as gain or sidelobes based on limited data on a few samples. In this report extensive data from production line antenna testing on several reflector designs was analyzed to determine the nature of the distributions. Although each antenna design is different, there is evidence that useful predictions can be made when the appropriate scale factors are used.
Preliminary development of a phased array near field antenna coupler
End-to-end testing of electronic warfare (EW) equipment at the organizational or flight lines level is accomplished by use of an antenna coupler which is placed over the EW system antenna. The coupler is used to inject a stimulus signal simulating a signal emanating from a distant radar, and to receive and detect the EW system response (EW transmit) signal. The coupler is used to determine the EW receiver sensitivity over a swept frequency coverage and the EW transmit gain and effective radiated power (ERP) versus frequency characteristics, as well as to determine the operating integrity of the EW antenna and transmission lines.
Ultra low sidelobe testing by planar near field scanning
An innovative technique has been developed for accurately measuring very low Sidelobe Antenna patterns by the method of planar near field probing. The technique relies on a new probe design which has a pattern null in the direction of the test antenna’s steered bean direction. Simulations of the near field measurement process using such a probe show that -60dB peak side-lobes will be accurately measured (within established bounds) when the calibrated near field dynamic range does not exceed 40 dB. The desireable property of the new probe is its ability to “spatially filter” the test antenna’s spectrum by reduced sensitivity to main beam ray paths. In this way, measurement errors which usually increase with decreasing near field signal level are minimized. The new probe is also theorized to have improved immunity to probe/array multipath and to probe-positioning errors. Plans to use the new probe on a modified planar scanner during tests with the AWACS array at the National Bureau of Standards will be outlined.
Characteristics and Capabilities of the Lewis Research Center high precision 6.7- by 6.7-M planar near-field scanner
The development of advanced spacecraft communication antenna systems is an essential part of NASA’s satellite communications base research and technology program. The direction of future antenna technology will be toward antennas which are large, both physically and electrically; which will operate at frequencies of 60 GHz and above; and which are nonreciprocal and complex, implementing multiple beam and scanning beam concepts that use monolithic semiconductor device technology. The acquisition of accurate antenna performance measurements is a critical part of the advanced antenna research program and represents a substantial antenna measurement technology challenge, considering the special characteristics of future spacecraft communications antennas.
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