AMTA Paper Archive
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Use of 'modern' general-purpose instruments in antenna measurement systems
The Electromagnetic Engineering Section of the National Research Council of Canada maintains a variety of pattern ranges and associated instrumentation to serve the needs of Canadian industry, government departments and universities. An extensive review of the facilities in 1983 revealed the need for significant modifications to maintain the current state-of-the-art level in antenna measurement technology.
Inverse synthetic aperture imaging radar
The accurate measurement of radar target scattering properties is becoming increasingly important in the development of stealth technology. This paper describes a low cost imaging Radar Cross Section (RCS) instrumentation radar capable of measuring both the amplitude and phase response of low RCS targets. The RCS instrumentation radar uses wideband FM wave-forms to achieve fine range resolution providing RCS data as a function of range, frequency and aspect. With additional data processing the radar can produce fully focused Inverse Synthetic Aperture Radar (ISAR) images and perform near field transformations of the data to correct the phase curvature across the target region. The radar achieves a range resolution of 4 inches at S-band and a sensitivity of –70 dBsm at a 30 ft range.
Design of a multipurpose antenna and RCS range at the Georgia Tech Research Institute
The design of a multipurpose Antenna/RCS range at GTRI is described. A novel approach to design of the far-field antenna range utilizes the bottom 40-foot section of a 130-foot windmill tower. The top 90-foot section is used as the main support for a slant RCS measurement range offering a maximum depression angle of 32º. A 100-tom capacity turntable, capable of rotating an M1 Tank, is located 150 feet from the 90-foot tower. The rigidity and stability of the tower should allow accurate phase measurement at 95 GHz for wind speeds up to 10 mph. In addition, a 500-foot scale-model range uses the ground plane effect to enhance target signal-to-noise and is designed to be useful at frequencies up to 18 GHz. Initially, the radar instrumentation to be utilized with the ranges includes several modular instrumentation systems and associated digital data acquisition equipment at frequency bands including C, X, Ku, Ka, and 95 GHz. The properties of these systems, which include coherence, frequency agility, and dual polarization, are discussed.
Near field measurement of very large antennas
Conventional pattern measurements are difficult to apply when the aperture is very large (250 lambda or more), particularly in the case of a relatively fragile antenna structure intended for a space application. Near field techniques can offer a solution, but may need a relatively large R.F. enclosure and custom instrumentation. This paper examines various alternative approaches in the case of the 15 m planar array under development at CAL for Radarsat. Specifically, the techniques under consideration include planar probing, cylindrical probing, planar cylindrical probing, intermediate range spherical probing, and some special variants. It is shown that the fact that the Radarsat antenna generates shaped beams as opposed to pencil beams impacts the relative accuracies achieved by these techniques to a very significant extent. The data collection and processing time, the size of the anechoic chamber needed, and the instrumentation requirement are also important considerations.
Application of digital filtering (FFT) techniques to the measurement of absorber and anechoic chamber properties
Three measurements commonly used in the absorber industry include absorber testing in NRL arches, testing absorber in waveguides, and testing performance of anechoic chambers. These measurements are closely related. All are looking for the size of one E field vector in the presence of several other E fields of variable amplitudes and phases. The information is extracted from the behavior of the sum as a function of some physical position change or frequency change. Computer controlled, synthesized sources and receivers have had two effects on the way these measurements may be taken and interpreted. First, the data are now available as a series of numbers in a computer instead of a series of lines on a piece of paper. Precise and elegant processing is available to extract the information from the data. Secondly, since frequency changes are made rapidly with this type of instrumentation, and precise position changes are made slowly, the data may be taken for many frequencies at each physical position, this makes it possible to extract additional information from the observed data changes as a joint function of frequency and position. These changes are spread throughout the block of data for signal amplitude vs position and frequency.
Conformal test coupler for measurements through antennas mounted on fuselages
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.
Troubleshooting test facilities with a high resolution instrumentation radar
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
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.
Two-dimensional RCS image focusing
A wide variety of precise, automatic instrumentation systems is currently available for RCS testing. These systems, either commercially available as integrated units or assembled from laboratory test instruments, can automatically measure the RCS of a target over fine frequency increments spanning wide bandwidths. When the frequency responses are measured for discrete increments of target rotation, the resulting two-dimensional (frequency-angle) data arrays can be processed to obtain two-dimensional RCS images.
Test methology for adaptive antenna systems
The evaluation of adaptive antenna systems expands the scope of conventional antenna testing. In addition to the conventional antenna parameters, the evaluation of an adaptive antenna system measures the effectiveness with which the adaptive antenna reduces interference. Adaptive antenna testing is conducted on a system level rather than the component-level tests of conventional antennas. The expanded scope of adaptive antenna testing requires more general test facilities, instrumentation, and test procedures. The additional requirements for adaptive antenna testing will be discussed.
Model 1603 compact range: a room sized measurement instrument
Harris Corporation has developed and introduced a miniature version of its shaped compact range called the Model 1603. This model is actually a scaled version of its very large compact ranges. The range features a three foot quiet zone in a very compact configuration, allowing the range to be set up in an anechoic chamber as small as a normal conference room. Performance features are equivalent to those achieved in large compact ranges by Harris, such as the Model 1640 with a forty foot quiet zone. Key features are very low quiet zone ripple, extremely low noise floor, and low cross polarization. This range can be used for the full gamut of precision RCS testing of small models or precision testing of antennas. It should also find wide application in production testing of these items. Harris can also provide turnkey compact range test systems based on the Model 1603 that use available radar instrumentation. Several of these miniature compact ranges have been delivered and are in use.
Making precision RCS measurements on a compact range using an HP8510 and an RF switching network
The development of a high efficiency compact range has made it possible to consider alternative equipment for making radar cross section measurements. Historically, high power radars were required to make measurements on low efficiency, high clutter ranges. Their high power and narrow pulse capability was essential in making precision measurements. Such instrumentation is complex and expensive. There is, however, a relatively inexpensive approach which uses test equipment commonly found in the laboratory. It is centered around an HP8510 network analyzer and an RF switching network.
Performance of gated CW RCS and antenna measurement
Conventional receivers for pulsed radar systems employ a wideband final filter that is matched to the pulse width and risetime. However for pulsed RCS measurements on small test ranges, instrumentation receivers with narrow IF bandwidth have proven useful. This paper analytically examines the differences between narrowband and matched filter instrumentation receivers and describes typical conditions under which gated CW measurements are made. Useful relationships between PRF and IF bandwidth are derived.
Modern dynamic RCS and imaging systems
This paper presents a conceptual overview of the instrumentation system and signal processing involved in dynamic RCS and Imaging measurement systems.
Recent advances in millimeter wave antenna measurement instrumentation
This paper describes recent advances in antenna measurement instrumentation for millimeter frequency applications. Application of a new, lightweight, programmable, ruggedized signal source at 40 and 60 GHz is outlined. An RF instrumentation system for millimeter frequency antenna range application is detailed. A millimeter-to-microwave converter is described which improves millimeter antenna range performance. System performance levels are predicted. Compact range configuration and operation at millimeter frequencies is detailed. Specific measurement examples are presented to demonstrate the measurement sensitivity which can be achieved.
A Wide band instrumentation radar system for indoor RCS measurement chambers
An instrumentation radar system suitable for collection of backscatter characteristics of targets in an indoor chamber was built and installed in the Ohio State University ElectroScience Laboratory. The radar is a pulsed system with continuous coverage from 2 to 18 GHz, and spot coverage from 26 to 36 GHz. The system was designed to have maximum flexibility for various test configurations, including complete control of the transmit waveform, H or V transmit polarization, dual receive channels for simultaneous measurement of like and cross polarization, greater than 100 dB dynamic range, and convenient data storage and processing. A personal computer controls the operation of the radar and is capable of limited data reduction and display functions. A mini-computer is used for more widely sophisticated data reduction and display functions along with data storage. This paper will present details of the radar along with measured performance capabilities of the system.
Texas Instruments' antenna test complex at McKinney
Texas Instruments' antenna test range complex consists of 15 new indoor ranges at the McKinney site. To meet projected business requirements, Texas Instruments initiated an aggressive antenna test range expansion and upgrade program in 1986. Construction of the new test range facility at McKinney is phase 1 of the plan which will be completed in the first quarter 1988. Phase 2, the construction of a new outdoor facility, will be completed in 1991. When completed the new facilities will be equipped with the latest technology in instrumentation and materials. A staff of antenna measurement experts maintain the ranges; they are equipped to make very short turn-around-time modifications to the range to meet special measurement requirements.
Improving antenna test range productivity
This paper presents the productivity improvements that are possible in complex antenna measurements using state of the art instrumentation. The productivity improvement is calculated for a hypothetical antenna, and from this productivity improvement manufacturing cost reductions and payback times are derived.
Instrumentation and computer control of the U.S. Army EPG compact range
Georgia Tech Research Institute has designed, developed and installed a large outdoor compact range for the U.S. Army Electronic Proving Ground at Ft. Huachuca, Arizona. Some of the unique hardware and software developed as part of the instrumentation and computer control tasks for the compact range are described.
The Effect of instrumentation VSWR on compact range ringdown performance
Analysis and measurement activities to quantify compact range feed/subreflector time domain response are described in this paper. Reflection properties of various components are quantified and their interaction studied. Results indicate that although the feed/subreflector interaction is a factor, reverberation is dominated by instrumentation interaction particularly in the case of small compact ranges.
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