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Paper not available for presentation.
Conventional methods for measuring the ohmic losses of radiating systems usually faces two basic difficulties: a) Need for accurate measurements, of very high VSWR values; b) Manufacturing of specially designed devices such as spherical short-circuit plates in order to terminate the radiating aperture. To circunvent such difficulties an experimental program is now under way in order to establish how accurately such losses can be determined from the associated increase in this antenna noise temperature. Experimental results obtained with the present method, for a corrugated feed horn at 4 GHz, compared quite favorably with those obtained by VSWR measurements using a spherical short-circuit termination. Proposed presentation will include: a) Error analysis; b) Experimental set-ups and discussion of measured results obtained so far; c) Possible extensions of the method. Conventional methods for measuring the ohmic losses of radiating systems usually faces two basic difficulties: a) Need for accurate measurements, of very high VSWR values; b) Manufacturing of specially designed devices such as spherical short-circuit plates in order to terminate the radiating aperture. To circunvent such difficulties an experimental program is now under way in order to establish how accurately such losses can be determined from the associated increase in this antenna noise temperature. Experimental results obtained with the present method, for a corrugated feed horn at 4 GHz, compared quite favorably with those obtained by VSWR measurements using a spherical short-circuit termination. Proposed presentation will include: a) Error analysis; b) Experimental set-ups and discussion of measured results obtained so far; c) Possible extensions of the method.
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.
This paper describes an antenna coupling “hat” and the automated measurement equipment for Multibeam Antenna (MBA) signature tests. The test equipment measures, records, and compares the insertion loss or the “signature” of the MBA prior to and after environmental tests; thereby determining the post-environmental test integrity of the MBA. Repeatable mechanical alignments to within ±0.125 inch and RF measurements to within ±0.5dB are required and achieved. This signature test has achieved substantial cost and schedule improvement by freeing up the heavily demanded compact antenna test range and by reducing MBA test time.
The septum polarizer is a four-port waveguide device illustrated in its basic form in Figure 1. The square waveguide at one end constitutes two ports because it can support two orthogonal modes. A sloping (or stepped equivalent) septum divides the square waveguide into two standard rectangular wavelengths sharing a common broadwall. With a properly designed septum, this device has interesting and useful properties.
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.
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.
The antenna measurement environment has changes substantially in the past few years. Designers are working with higher frequencies than were practical before and new techniques require both phase and amplitude data for design optimization. This has created new demands for positioner designs. This paper describes how modern mechanical design tools together with modern components were used to develop a new generation positioner for antenna measurement.
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.
A new technique with utilizes Digital Signal Processing algorithms in conjunction with Frequency Domain Reflectometry (FDR) to characterize transmission line system is discussed. Algorithms are developed which include tbe Windowed Fast Fourier Transform (WFFT) to determine the location and amplitude of single or multiple mismatches in a single pass. Refinement techniques include quadratic interpolation for increased location and amplitude accuracy and correlation for rejecting harmonics and high power “foreign” (interference) signals.
The abstract for this paper has been lost
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.
Background reflections from range features are a major source of error in Radar Cross Section measurements. Direct phasor subtraction of the background is possible only if the background signals prior to and after target mounting are relatable. If a complex drift, a, is allowed, use of a four-measurement technique, including a reference, can permit elimination of both a and the background.
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).