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This presentation will focus on the recently revised ANSI C95 RF Radiation Exposure Standard. Some of the research background for the new standard will be given, and its impact will be explained. Instrumentation guidelines for measuring potentially hazardous fields will be presented. The possible damaging effects of non-ionizing RF radiation is receiving increased attention in the public eye, and it behooves the practicing antenna engineer to be aware of the potential dangers to health and safety from exposure of RF energy.
The compact range is an electromagnetic measurement system used to simulate a plane wave illuminating an antenna or scattering body. The plane wave is necessary to represent the actual use of the antenna or scattering from a target in a real world situation. Traditionally, a compact range has been designed as an off-set fed parabolic reflector with a knife edge or serrated edge termination. It has been known for many years that the termination of the parabolic surface has limited the extent of the plane wave region or, more significantly, the antenna or scattering body size that can be measured in the compact range. For example, the Scientific Atlanta (SA) Compact Range is specified to be limited to four foot long antennas or scattering bodies as shown in their specifications. Note that the SA compact range uses a serrated edge treatment as shown in Figure 1. This system uses a parabolic reflector surface which is approximately 12 square feet so that most of the reflector surface is not usable based on the 4 foot square plane wave sector. As a result, the compact range has had limited use as well as accuracy which will be shown later. In fact, the compact range concept has not been applied to larger systems because of the large discrepancy between target and reflector size. In summary, the target or antenna sizes that can be measured in the presently available compact range systems are directly related to the edge treatment used to terminate the reflector surface.
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.
Progress is reported on use of synchro to digital converter modules. The particular modules applied are 16 bit SDC-361 units, manufactured by ILC Data Device Corporation. Two converters are included in each pf five Model SD-2000 synchro monitors designed and fabricated by Petri Associates and acquired by the Lockheed-California Company for the antenna test facility of the Kelly Johnson R&D Center at Rye Canyon. Applications depended upon learning how Type 23TX6 synchro transmitter pairs in the model towers and elevation-over-azimuth positioners at the facility can be electrically zeroed to match the 16 bit resolution of SDC-361 synchro to digital converters.
This paper describes the new antenna test facility under construction at General Electric Space Systems Division in Valley Forge, PA. The facility consists of a shielded anechoic chamber containing both a Compact Range and a Spherical Near-Field Range. In addition, it provides for a 700’ boresight range through an RF transparent window. The facility will be capable of testing antenna systems over a wide frequency range and will also accommodate an entire spacecraft for both system compatibility and antenna performance tests.
The measurement of microwave antennas indoors began with the advent of commercial absorbing material. The use of absorbers can be traced back to a 2 gHz material developed by the Dutch in the Thirties. During the Forties, considerable progress was made on absorbing materials, but even after World War II, security considerations limited the application. Some materials found use as indoor shields for antenna tests, but limited bandwidth limited the utility of these materials. When a broad band absorber was developed the antenna experts did not believe that this material would be made commercially because they presumed a limited market.
This paper describes the development and evaluation of a general purpose ground-reflection antenna test range operated by the Council for Scientific and Industrial Research (CSIR). The range is 500 m long and the design is such to allow operation in the ground-reflection mode at L, S, and X bands. The physical configuration of the range is presented to illustrate some of the practical problems experienced in implementing the range design. An experimental evaluation programme was conducted to determine the state of the incident field over the test aperture. Some of these results are presented to show the performance achieved with the range design.
A classical problem encountered when measuring the far-field radiation pattern of an antenna in a medium-distance range is the degradation that occurs when undesirable reflections (from the ground or nearby objects) are present. To reduce this problem, the source and test antennas are often installed on towers to remove them from the reflective objects, RF absorptive materials are used to reduce the magnitude of the reflected signals, and often the reflective objects in the range are adjusted in order to null out the reflections and “clean up” the range. These solutions are often limited in their effectiveness and can be prohibitively expensive to implement.
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.
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.
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
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.
An 80 element linear phased array antenna was measured in the nearfield. The insertion phase and amplitude for each element were measured while the 8-bit ferrite phase shifters were individually stepped through their degrees for freedom.
Test techniques and test results will be presented on Compact Range testing of a 1.9m offset reflector at 20/30 GHz. The antenna is part of a demonstration model for an intersatellite link antenna system.
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.
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.
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.