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Historically, radar imaging sensors have been divided into two categories, SAR and ISAR systems. Even though they are solving the same imaging prob lems the data collection environment is dramatically dif ferent between the two. Consequently, the particular waveforms selected for the two have been different. The primary waveform for ISAR RCS measurement systems is stepped frequency, while the FM-chirp (linear-FM) waveform has been used much more often in SAR applications. However, recently this boundary has been blurred, in that stepped frequency radars are being applied to long range dynamic measurements, long the domain of chirped waveforms, and conversely the chirped waveform has been applied to target RCS mea surements of both static and dynamic targets. This paper will address the system parameter tradeoffs involved in selecting between the two waveforms for two different applications; (i) near range static target imaging, and (ii) far range dynamic target imaging. The system parameter tradeoffs involve RF bandwidth, PRF, scene size, trans mitter power, doppler frequency spread of target, etc. The advantages, disadvantages, and inherent limitations of each waveform will be analyzed to yield a better understanding of the tradeoffs involved, and the data collection examples will further illustrate these tradeoffs for the two specific applications.
Radar cross section measurements must be performed in a wide variety of situations throughout development of a new vehicle. In these days of smaller budgets, it is vitally important that the right things get measured, at the right time in the program, with the right accuracy, and that these measurements be integrated into the development process in the right way. After delivery, the measurement system must be confidently usable by the user organization, with a minimum of outside to ensure that the vehicle is maintained. Many of the key programs in this area were begun before modern measurement technology was known to be capable of providing detailed diagnostic measurements. Consequently, specifications did not consider what can be easily measured with today's modern diagnostic radars. This paper addresses how mcxlern diagnostic radar cross section measurements can be exploite4:l to make the specification, development, pnxluction, and testing phases much more efficient than they have been in the past.
Radar cross section measurements must be performed in a wide variety of situations throughout development of a new vehicle. In these days of smaller budgets, it is vitally important that the right things get measured, at the right time in the program, with the right accuracy, and that these measurements be integrated into the development process in the right way. After delivery, the measurement system must be confidently usable by the user organization, with a minimum of outside to ensure that the vehicle is maintained. Many of the key programs in this area were begun before modern measurement technology was known to be capable of providing detailed diagnostic measurements. Consequently, specifications did not consider what can be easily measured with today's modern diagnostic radars. This paper addresses how mcxlern diagnostic radar cross section measurements can be exploite4:l to make the specification, development, pnxluction, and testing phases much more efficient than they have been in the past.
Photogrammetry, as its name implies, is the science of obtaining precise coordinate measurements from photographs. Until recently, photo-grammetry used film photographs taken with specially designed, high-accuracy film cameras. With the development of h igh resolution solid-state imaging sensors, a new era in photogrammetry has arrived. Video grammetry, as it is often called, provides far faster results and greater capability than film based photogrammetry, and therefore eliminates the major impediments to more widespread use of photogrammetry in the antenna manufacturing industry. Video-grammetry is a powerful enabling technology that not only performs many current measurement tasks faster and more efficiently th an existing technologies, but also, now makes feasible many types of measurements, that pre viously were not practical or possible. The capability for quick, accurate, reliable, in place measurements of static or moving objects in vibrating or unstable environments is a powerful combination of features all in one package. There are many applications for this emerging new technology in the antenna manufacturing industry. This paper will describe some of the successfu l implementation of video-grammetry into the MSA T program at Hughes Space and Communications Company located in Los Angeles, California.
Photogrammetry, as its name implies, is the science of obtaining precise coordinate measurements from photographs. Until recently, photo-grammetry used film photographs taken with specially designed, high-accuracy film cameras. With the development of h igh resolution solid-state imaging sensors, a new era in photogrammetry has arrived. Video grammetry, as it is often called, provides far faster results and greater capability than film based photogrammetry, and therefore eliminates the major impediments to more widespread use of photogrammetry in the antenna manufacturing industry. Video-grammetry is a powerful enabling technology that not only performs many current measurement tasks faster and more efficiently th an existing technologies, but also, now makes feasible many types of measurements, that pre viously were not practical or possible. The capability for quick, accurate, reliable, in place measurements of static or moving objects in vibrating or unstable environments is a powerful combination of features all in one package. There are many applications for this emerging new technology in the antenna manufacturing industry. This paper will describe some of the successfu l implementation of video-grammetry into the MSA T program at Hughes Space and Communications Company located in Los Angeles, California.
With modern range hardware, it is possible to per form ultra wide band frequency measurements with out changing the range configuration. This has not been possible with existing chamber antennas be cause they have been limited in bandwidth in or der to provide the desired illumination. In addition, these antennas have not considered scattering issues, even though one goes to great lengths to minimize reflections within a chamber. The rolled edge Slot line Bowtie Hybrid (SBH) antenna has been used for ultra wide band applications for many years. How ever, it can not meet the range scattering require ments due to its structure (large rolled edges). In this paper, a new R-Card version of the SBH an tenna is presented. It is fabricated by integrating resistive sheets (R-Cards) into the blended rolled edge concept so that both the ultra wide band and low RCS antenna features can be obtained simul taneously. Further, by employing resistive sheets, the R-Card SBH antenna can provide the desired constant beamwidth to fully illuminate the target zone. Measured and calculated results are presented to demonstrate the performance of this new antenna.
With modern range hardware, it is possible to per form ultra wide band frequency measurements with out changing the range configuration. This has not been possible with existing chamber antennas be cause they have been limited in bandwidth in or der to provide the desired illumination. In addition, these antennas have not considered scattering issues, even though one goes to great lengths to minimize reflections within a chamber. The rolled edge Slot line Bowtie Hybrid (SBH) antenna has been used for ultra wide band applications for many years. How ever, it can not meet the range scattering require ments due to its structure (large rolled edges). In this paper, a new R-Card version of the SBH an tenna is presented. It is fabricated by integrating resistive sheets (R-Cards) into the blended rolled edge concept so that both the ultra wide band and low RCS antenna features can be obtained simul taneously. Further, by employing resistive sheets, the R-Card SBH antenna can provide the desired constant beamwidth to fully illuminate the target zone. Measured and calculated results are presented to demonstrate the performance of this new antenna.
This paper describes an adaptive array that was designed to improve the carrier-to-interference ratio (C/I) delivered to base station radios by 6 dB in U.S. 800 MHz analog cellular networks. The C/I performance of this kind of system is difficult to verify, because it cannot be characterized in terms of traditional antenna specifications such as beamwidth and directivity. This paper describes a simple C/I measurement strategy in which the antenna under test and a collocated reference antenna are placed into simultaneous operation in an actual cellular network. Relative C/I performance can then be deduced from a statistical analysis of the antenna outputs. This method is particularly well-suited to software radio based systems, because no special test equipment is required to gather the necessary data.
This paper describes an adaptive array that was designed to improve the carrier-to-interference ratio (C/I) delivered to base station radios by 6 dB in U.S. 800 MHz analog cellular networks. The C/I performance of this kind of system is difficult to verify, because it cannot be characterized in terms of traditional antenna specifications such as beamwidth and directivity. This paper describes a simple C/I measurement strategy in which the antenna under test and a collocated reference antenna are placed into simultaneous operation in an actual cellular network. Relative C/I performance can then be deduced from a statistical analysis of the antenna outputs. This method is particularly well-suited to software radio based systems, because no special test equipment is required to gather the necessary data.
A novel test article, the Transformable Scale Aircraft-Like Model (TSAM), which holds great promise for validating complex computational electromagnetic (CEM) codes more effectively is described. The novelty of TSAM is in the use of removable/replaceable canonical shaped structural components. The complexity in TSAM can be tailored to the modeling capabilities of the CEM code under test allowing discrepancies between measurement and simulation to be more explainable. A set of preliminary measurements on TSAM have been made and the results compared to calculations from the General Electromagnetic Model for the Analysis of Complex Systems (GEMACS) program (1), a standard CEM code.
A novel test article, the Transformable Scale Aircraft-Like Model (TSAM), which holds great promise for validating complex computational electromagnetic (CEM) codes more effectively is described. The novelty of TSAM is in the use of removable/replaceable canonical shaped structural components. The complexity in TSAM can be tailored to the modeling capabilities of the CEM code under test allowing discrepancies between measurement and simulation to be more explainable. A set of preliminary measurements on TSAM have been made and the results compared to calculations from the General Electromagnetic Model for the Analysis of Complex Systems (GEMACS) program (1), a standard CEM code.
The development* of a real time electronic system to accurately measure the pattern of high gain, ultralow sidelobe level antennas in the presence of multipath scatterers is described. Antenna test ranges contain objects that scatter the signal from the transmitting antenna into the main beam of a receiving antenna under test (AUT), thereby creating a multipath channel. Large measurement errors of low sidelobes can result. The design and computer simulation of an Antimultipath System (AMPS) is complete. Fabrication of a feasibility demonstration model AMPS to operate with rotated AUTs to suppress indirect (scattered) components and permit accurate pattern measurements is almost done. Results to date show the likelihood of measuring sidelobe levels 60 dB below the main beam. * This project is sponsored in part by the Air Force Material Command under Rome Laboratory Contract Nos. F30602-92-C-0009, Fl9628-92-C-0130 and F 19628-93-C-02 l4.
The development* of a real time electronic system to accurately measure the pattern of high gain, ultralow sidelobe level antennas in the presence of multipath scatterers is described. Antenna test ranges contain objects that scatter the signal from the transmitting antenna into the main beam of a receiving antenna under test (AUT), thereby creating a multipath channel. Large measurement errors of low sidelobes can result. The design and computer simulation of an Antimultipath System (AMPS) is complete. Fabrication of a feasibility demonstration model AMPS to operate with rotated AUTs to suppress indirect (scattered) components and permit accurate pattern measurements is almost done. Results to date show the likelihood of measuring sidelobe levels 60 dB below the main beam. * This project is sponsored in part by the Air Force Material Command under Rome Laboratory Contract Nos. F30602-92-C-0009, Fl9628-92-C-0130 and F 19628-93-C-02 l4.
Boresight and gain determination play an important role in antenna measurements. Traditionally, on outdoor ranges, optical methods are used to determine the boresight. Accuracy requirements better than 0.001 degrees are difficult if not impossible to obtain on outdoor ranges using these method since the effect of incident electromagnetic fields are not taken into account. On indoor ranges no technique is available at present that achieves the desired accuracy demands. In this paper, an improved method for boresighting will be presented. It will be shown that using this technique, desired accuracy demands on both outdoor and indoor can be obtained. Furthermore, the method can also be combined with accurate gain calibration. Advantages and disadvantages of this technique will be discussed.
Boresight and gain determination play an important role in antenna measurements. Traditionally, on outdoor ranges, optical methods are used to determine the boresight. Accuracy requirements better than 0.001 degrees are difficult if not impossible to obtain on outdoor ranges using these method since the effect of incident electromagnetic fields are not taken into account. On indoor ranges no technique is available at present that achieves the desired accuracy demands. In this paper, an improved method for boresighting will be presented. It will be shown that using this technique, desired accuracy demands on both outdoor and indoor can be obtained. Furthermore, the method can also be combined with accurate gain calibration. Advantages and disadvantages of this technique will be discussed.
Optical surveying techniques with theodolites have been utilized for many years for static measurements of reflector antennas. This paper reports on updated optical surveying systems used to measure the accuracies and structural deformations of reflector antennas. Deformations of large Cassegrain tracking antennas during elevation rotation and a fixed, billboard-style compact range reflector over time are discussed. A simple surveying method is shown for the integrated measurement of Cassegrain antennas (both primary and secondary reflectors) from near the primary vertex. Other topics covered include accurate prediction of interpolated gravity deformations of rotating reflectors based on a small measurement sample, and a method for taking differences between measurements. The use of EDM (Electronic Distance Measurement) theodolites as well as angle-only devices is described, along with software which manages both the measurement and data-reduction systems.
Optical surveying techniques with theodolites have been utilized for many years for static measurements of reflector antennas. This paper reports on updated optical surveying systems used to measure the accuracies and structural deformations of reflector antennas. Deformations of large Cassegrain tracking antennas during elevation rotation and a fixed, billboard-style compact range reflector over time are discussed. A simple surveying method is shown for the integrated measurement of Cassegrain antennas (both primary and secondary reflectors) from near the primary vertex. Other topics covered include accurate prediction of interpolated gravity deformations of rotating reflectors based on a small measurement sample, and a method for taking differences between measurements. The use of EDM (Electronic Distance Measurement) theodolites as well as angle-only devices is described, along with software which manages both the measurement and data-reduction systems.
In this paper, we present a new technique for measuring the input impedance of balanced antenna systems. The process uses standard two-port scattering parameters for balanced antennas, feeding each of the balanced input ports as the port of a two-port. The scattering-parameters will be related to the designed input impedance which may be obtained by post-processing the data. In addition, the scattering-parameters may be used to check for the assumed balance of the system. Both experimental and simulated results will be presented to validate the technique.
In this paper, we present a new technique for measuring the input impedance of balanced antenna systems. The process uses standard two-port scattering parameters for balanced antennas, feeding each of the balanced input ports as the port of a two-port. The scattering-parameters will be related to the designed input impedance which may be obtained by post-processing the data. In addition, the scattering-parameters may be used to check for the assumed balance of the system. Both experimental and simulated results will be presented to validate the technique.
Modem antenna measurements require not only fast measurement but also quick transport of data to a multitude of computer for post-processing and analysis. Issues in the of a networked computer architecture for an antenna measurement laboratory are discussed. A case study is presented to highlight some of the considerations. Description and performance of a facility employing the concepts are included.