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Antenna gain is traditionally measured by comparing the output of the antenna under test to that of a known gain standard. Many modern antennas, and particularly scanning arrays, include significant resistive losses or amplifiers to overcome these losses. When the antenna includes amplifiers it is clear that the measurement must be corrected since the amplifier gain has a different effect than the antenna gain. It is less obvious that even without amplifiers the traditional gain measurement is not adequate to predict system range is the sky temperature is different than the antenna temperature. Some of the approximations involved are discussed below, starting with conventional antennas.
This paper was written to promote discussion among antenna engineers about exciting new possibilities in microcomputer applications. To provide a stimulus, a home computer, printer, and plotter were used while writing FORTH words to describe three dimensional rotations of antenna positioners and aircraft models mounted upon them. Emphasis is placed on description of rotations by means of three body angles and associated direction cosine array on one hand and description in terms of rotation about a rotor axis with fixed direction on the other hand. Examples are given for a range with dish antenna transmitter, model tower, and aircraft model. Line drawings are all orthographic projections in response to few high level FORTH words.
Today’s broadband electronic warfare systems are more sophisticated and complex than ever before. Many systems require that component and subsystems be characterized more extensively than in the past. This leads to the need for high-speed automated antenna measurement over a broad frequency band. For example, a program currently in progress requires that phase and amplitude measurements be made on the antenna system for four different polarizations at approximately 400 frequencies over a 9:1 bandwidth. This is achieved with an automated test system using broadband instruments which are capable of rapidly stepping through frequencies while maintaining measurement accuracy. This paper will review some of the current trends in test requirements, the problems associated with this increased demand for data and alternative solutions. Data will be presented to illustrate achievable performance.
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.
As today’s electronic support measures (ESM) systems become more complex so must the test equipment required for qualification and final acceptance tests. Tests and test facilities have become more complex, costly and massive when these ESM systems are integrated into vehicle size structures which must be tested as a unit. This paper describes an automated anechoic chamber which was built to solve some of the special problems associated with the testing of a physically large, electronically sophisticated ESM system. Some features of the automation thought to be unique are the methods used to position the test antennas without any required operator interaction. Other unique features of the design include methods of aligning the test article to the source antennas and the technique used for chamber qualification.
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.
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.
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.
This paper describes a diagnostic RCS measurement system which uses a low-power, wideband, linear-FM radar to provide RCS responses of targets as a function of frequency, range, cross range, and angle. Range and frequency responses are produced by using an FFT analyzer and a desktop computer to perform on-line signal processing and provide rapid access to final results. Two-dimensional maps of the target RCS distribution in range and cross range are obtained by offline processing of recorded data. The system processes signals resulting from a swept bandwidth exceeding 3GHz to provide range resolution of less than 10 cm. The various operating modes of the instrumentation provide a powerful tool for RCS diagnostic efforts in which individual scattering sources must be isolated and characterized. Several examples of experimental results and presented to demonstrate the utility and performance limits of the instrumentation. The examples include results obtained from measurements of a number of simple and complex shapes and of some commercially available radar absorbing materials.
Since 1976 the Technical University of Denmark (TUD), sponsored by the European Space Agency (ESA), has developed a facility for spherical near-field scanning of antennas. This range has been in operation since April 1979 and has undergone continuous refinement. Some of the measurement results obtained with the facility as well was various aspects of the measuring system itself have been published from time to time (Ref. 1-5).
As a part of the research project in Denmark on spherical near-field measurements, a number of FORTRAN programs for transformation of measured near-field data has been developed since 1976. Based on earlier work by Jensen, Wacker and Lewis, the series of programs can be summarized as follows: SNIFT (1976) Without probe correction based on a program by Lewis, NBS. Small antennas only. SNIFTB (1977) First program with probe correction. Maximum antenna diameter 25 wavelengths due to numerical instabilities. SNIFTC (1978) With probe correction. Numerically stable. Antenna size limited by the requirement that a full sphere of measured data must be contained in core memory during execution. SNIFM (1980) Segmented program with segmentation of data written for a HP1000 computer only. Antenna diameter limited to 120 wavelengths due to certain arrays in addressable memory. The new computer program is based on the experience with spherical near-field measurements at the Technical University of Denmark.
Spherical near-field testing of antennas requires the acquisition of a great volume of data. In general, to compute the far-field of the antenna under test in any direction requires the acquisition of data at sample intervals related to the size of the antenna under test over a spherical sampling surface completely enclosing the antenna under test. This data must also be sampled as a function of probe orientation. Even for the simplest possible case, two probe orientations (or two probes) must be used.
A set of near-field measurements has been performed by combining the methods of non-probe-corrected spherical near-field scanning and gain standard substitution. In this paper we describe the technique used and report on the results obtained for a particular 24 inch 13 GHz paraboloidal dish. We demonstrate that the gain comparison measurement used with spherical near-field scanning give results in excellent agreement with gain comparison used with compact range measurement. Lastly we demonstrate a novel utilization of near-field scanning which permits a gain comparison measurement with a single spherical scan.
This paper reports on research being conducted at Georgia Tech on the spherical surface near-field measurement technique. The popularity of the spherical surface near-field measurement technique is indicated in the list of near-field ranges as shown in Table I. This popularity is, in large part, due to the availability of the scientific Atlanta Spherical Near-Field Antenna Analyzer. Specifically, the paper reports on the status of (1) the Georgia Tech spherical surface near-field range, (2) comparison of non-probe compensated spherical surface near-field to far-field transformation techniques, (3) a probe position error compensation technique for spherical surface measurements, and (4) alternative spherical surface near-field to far-field transformations which include probe compensation.
Conventional antenna test techniques – both far field “slant ranges” and near field – pose limitations for radiative RF testing of satellite antennas and payload systems, of increasing complexity in terms of size, operating frequencies, configurations and technology, particularly when such systems need to be evaluated in their “in-situ” locations on typical satellite platforms, in their flight configurations. Often, combination of tests and simulation has been the only recourse for evaluating system performance. In this paper, a methodology is proposed to achieve these test objectives via the use of a suitable configures, wideband, large (Quiet zone 7m x 5m x 5m), compact range for evaluation od system parameters like E.I.R.P., G/T, C/I, BER, and RF sensing performances. The test plan and evaluation schemes appropriate for these tests are elaborated to demonstrate the validity and usefulness of the approach. For some specific parameters like C/I (for a multibeam payload system) and the radar parameters (for a satellite borne radar system), it turns out that the proposed test methodologies offer the only realistic and complete tool for evaluating such system at satellite level.
Spherical near-field testing and other specialized antenna measurements require precise range and positioner alignment. This paper presents a method based on optical techniques to conveniently measure and monitor both range alignment and the positioner axis orthogonality and intersection. The hardware requirements consist of a theodolite and a unique target mirror assembly viewable from either side.
The development of a high resolution instrumentation radar is described. This radar constructed at X-band uses a chirp waveform to achieve a 4.9” range resolution capability. A key feature of this development is the use of cos2 x amplitude weighting to control the range sidelobes. An example of a high resolution radar response is described.
The operation and application of the Scientific-Atlanta Model 1784/ 1785 Millimeter-Wave to Microwave Converter is discussed. The converter allows single channel or multi-channel coherent measurements to be made with excellent sensitivity at Millimeter-wave frequencies. The converter improves the dynamic range of Millimeter-wave measurements by up to 30 dB over conventional measurements made with broad-band microwave receivers operating at high mixer harmonic numbers.
Test results will be presented for a four foot S-Band reflector antenna together with the compact range modification and test verification at 2.2 GHz. Similarly compact range test results will be presented for an eight foot K-band reflector antenna at 23 GHz.
A General Extrapolation Technique which corrects for the effects of ground reflections in absolute gain measurements is described. It utilizes the Extrapolation Method developed at NBS which, in its present form, utilizes only amplitude versus distance data. However, for broadbeam antennas such as those encountered below 1 GHz, ground reflections may produce unwanted oscillations in the amplitude versus distance data. However, for broadbeam antennas such as those encountered below 1 GHz, ground reflections may produce unwanted oscillations in the amplitude versus distance data. Hence the data are not amenable to the curve fitting procedure of the Extrapolation Method. This problem can be overcome by including phase versus distance information to negate the effects of ground reflections.