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Antenna Polarization measurements
In recent years there has been an increasing requirement for more extensive and precise measurements of the polarization properties of antennas. Some of the more conventional polarization measurement techniques are no longer applicable because of the required measurement time or the achievable accuracy. This presentation is an overview of polarization measurement methods which may be employed on far-field antenna ranges. Instrumentation requirements and sources of error are also included.
IEEE 488 System Concepts
This paper will present a basic explanation of the IEEE Standard 488-1978, concerning what it is, and how and why it concerns people in the RF world. In addition, the practical side of the IEEE 488 will be discussed, touching on such topics as the types of instrumentation available with IEEE, custom systems design and installation, the new one-chip interfaces, computer enhancement of measurements and generation of analytical graphic data. This up dated review is made with an eye towards enhancing both speed and accuracy of contemporary antenna testing techniques.
Estimating the accuracy of gain measurements
A limited number of power gain measurements for some broadband airborne antennas were analyzed by comparing the measured values to the predictions from hypothetical models for the antennas. The difference between the predicted gain and measured gain is defined as the measurement uncertainty. The measurement uncertainties were statistically analyzed to determine the accuracy of the gain measurements. The results indicated that 79 percent of measurement uncertainties were written 1.5dB.
Wide aperture microwave noise oscillators for antenna parameter measurements
Wide aperture noise sources for accurate antenna energy parameters measurements are described. Measurement methods utilizing radiators with high equivalent noise temperature (104-105)K are discussed as well as their construction. Antenna equivalent efficiency, gain and disspation coefficient can be measured with accuracy (5-10%) depending on the frequency range.
Automated Phase/Amplitude EHF Measurement System
An automated, computer-controlled measurement system capable of conducting transmission and reflection measurements on components over the 40 to 47 GHz frequency range is described. The measurement system utilizes harmonic mixing in conjunction with a phase locked, dual channel receiver to downconvert signals in the 7 GHz bandwidth to a lower intermediate frequency (1 KHz) where phase and amplitude measurements are made. The system is capable of operating over a dynamic range in excess of 50 dB when used with an EHF source producing a minimum –10 dBm output. Following a description of the system and its operation, some performance characteristics are presented. The measurement system accuracy is demonstrated using two types of reference standards: (1) a rotary vane attenuator for the transmission measurements, and (2) a set of reduced-height waveguide VSWR standards for the return loss measurements. Results obtained using these standards have indicated that measurement accuracies of 0.25 dB and 30 are achievable over a 50 dB dynamic range.
Configuration of spherical near-field ranges
In principle, spherical near-field scanning measurements are performed in the same way as conventional far-field measurements except that the range length can be reduced. This provides a natural advantage to scanning in spherical coordinates over other coordinate systems due to the steady availability of equipment. However, special considerations must be given to near-field range design because of the necessity for phase measurement capability, mechanical accuracy and the need to handle large quantities of data. Based on experience with spherical near-field measurements carried out during verification testing of a spherical near-field transformation algorithm, we discuss the practical aspects of constructing a near-field range. In particular we will consider range alignment procedure, engineering of the RF signal path and times for data collection and processing.
The Orbiting Standards Package: A Recalibratable Satellite Instrument Assembly for Measuring Large Earth Station Antennas
The concept of an Orbiting Standards Package (OSP) has been discussed as a means of making direct measurements of fields, patterns, and polarization states of signals radiated from large earth station antennas. It would also have the capability of producing test field of known intensities and arbitrary but well-defined polarization states, thereby enabling the determination of such parameters as G/T and Effective Receiving Area of earth stations. Recent developments in microwave six-port networks and in standard antennas would permit the all-electronic generation and detection of these signals. Moreover, it appears possible to recalibrate the satellite standards package to laboratory state-of-the-art accuracy following launch.
Automated digital antenna measurements
The Automated Digital Antenna Measurement (ADAM) System developed by Flam & Russell, Inc. (FR) relieves the antenna engineer and technician from the constraint of designing a test plan/procedure dictated by the architecture of his automated test system. By contrast, ADAM’s flexibility allows the user to design a test configuration and interface with that instrumentation which is optimum for the performance evaluation of the antenna system under test in terms of data rate and accuracy. Further, as the test needs and configurations change, ADAM changes with them. For instance, if the engineer is testing antennas for a phase/amplitude interferometer, the test set-up might include a Systron-Donner frequency synthesizer and a Scientific-Atlanta receiver – thus sacrificing speed for accuracy. The same facility could be used later in the day for production testing where frequency accuracy is less critical and high data rates are the objective. In this case the signal source might be a voltage controllable Wiltron sweeper and the receiver an HP network analyzer. ADAM accommodates this change by merely identifying the test equipment through a menu.
Millimeter wavelength measurements of large reflector antennas
An instrument has been built which allows the electromagnetic measurement of the surface accuracy of a large millimeter-wavelength antenna. The University of Texas 4.9 m radio telescope has been measured with this technique at 86.1 GHz to an accuracy of 4 µm at the surface. Our technique is an interferometric one which is fast, accurate, and able to measure the whole antenna surface at once. While the technique is illustrated by its use on a large antenna, it could be used in a near field measurement of a smaller antenna. Several antenna surface maps are presented. A comparison of run-to-run repeatability was made. The technique itself was tested by deforming the antenna surface in a known way and subsequently detecting the deformation. In addition, important factors which influence the overall error budget have been identified. These include errors in setting the antenna angular position and fluctuation noise in the atmosphere and electronics. An instrument has been built which allows the electromagnetic measurement of the surface accuracy of a large millimeter-wavelength antenna. The University of Texas 4.9 m radio telescope has been measured with this technique at 86.1 GHz to an accuracy of 4 µm at the surface. Our technique is an interferometric one which is fast, accurate, and able to measure the whole antenna surface at once. While the technique is illustrated by its use on a large antenna, it could be used in a near field measurement of a smaller antenna. Several antenna surface maps are presented. A comparison of run-to-run repeatability was made. The technique itself was tested by deforming the antenna surface in a known way and subsequently detecting the deformation. In addition, important factors which influence the overall error budget have been identified. These include errors in setting the antenna angular position and fluctuation noise in the atmosphere and electronics.
An Antenna pattern arch for measurements over sea water
The Naval Underwater Systems Center has under construction an antenna pattern arch for measuring the radiation pattern of submarine antennas protruding above the sea water surface. The 70-foot radius tripodal arch is constructed of laminated wood members located over a 66-foot by 93-foot concrete pool which will contain a six inch depth of sea water. A well is located off-center in the pool for mounting the antenna under test. Pattern measurements will be made from 20 MHz to 2 GHz and at antenna heights of up to 15-feet above the sea water. Heretofore this over-sea water pattern information has been unobtainable. The important criteria for far-field antenna measurements are mentioned. The Numerical Electromagnetic Code (NEC) was used to model typical submarine antennas at various frequencies in order to predict the accuracy of the arch range. NEC uses moment methods to determine the arch patterns and the far-field patterns.
Transmission Lines/Antenna Systems Analysis
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.
Automated, broadband antenna measurements
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.
Planar Near-Field Measurements Using Hexagonal Sampling
This paper describes a new planar near-field measurement technique in which near-field data is collected in a hexagonal rather than a rectangular format. It is shown that the hexagonal method is more efficient than the rectangular technique in that a lower sampling density is required and the hexagonally shaped measurement surface is more compatible with most antenna apertures than the conventional rectangular measurement surface.
A Dual shaped compact range for EHF antenna measurements
A dual offset shaped reflector compact range is described. Improvements over the traditional single reflector, apex-fed compact range are outlined and discussed. A design plan for a dual offset shaped reflector compact range for EHF antenna measurement is presented.
A New antenna test facility at General Electric Space Systems Division in Valley Forge, PA.
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.
G/T measurement of highly directive antenna systems
A technique for improving the accuracy of G/T measurements of highly directive antennas is introduced. The technique presents was developed to overcome uncertainties in ephemeral information, antenna positioning, system gain stability, and other random and nonrandom phenomena. The particular application discussed uses Casseiopeia-A as a noise source but the technique can be adapted for use with other extraterrestrial noise sources.
VHF antenna range design
The design concept for outdoor antenna ranges operated at frequency 50 MHz is discussed. The antenna range is designed for test of VHF antennas mounted on a full-scale satellite mockup. Due to the large size of test objects, a tradeoff between cost and test accuracy among carious range configurations is addressed. Due to near-omni directional characteristics of test antennas, the multipath interference may be severe. The interference ground reflection, surface wave and multiple scattering are quantified and evaluated.
Automated wideband, phase coherent polarimetric radar cross section measurements
This paper describes the equipment, mechanics and methods of one of the outdoor ranges at Teledyne Micronetics. A computer controlled microwave transceiver uses pulsed CW over a frequency range of 2-18 GHz to measure the amplitude, phase and polarization of the signal reflected off the target. The range geometry, calibration and analysis techniques are used to optimize measurement accuracy and characterize the target as a set of subscatterers.
A Figure of merit for evaluating signal processing antennas
In recent years a new class of reflector antennas utilizing array feeds has been receiving attention. An example of this type of antenna is a reflector utilizing a moveable array feed for beam steering. -. Due to the circuitry required to adjust the weights for the various feed array elements, an appreciable amount of loss can be introduced into the antenna system. One technique to overcome this possible deficiency is to place low noise amplifiers with sufficient gain to overcome the weighting function losses just after each of the feed elements. In the evaluation of signal processing antennas that employ amplifiers the standard antenna gain measurement will not be indicative of the antenna system’s performance. In fact, by only making a signal measurement, the antenna gain can be made any arbitrary value by changing the gains of the amplifiers used. In addition, the IEEE Standard Test Procedures for Antennas  does not cover the class of antennas where the amplifier becomes part of the antenna system. There exists a need to establish a standard of merit or worth for multi-element antenna systems that involve the use of amplifiers. This communication presents a proposed figure of merit for evaluating such antenna systems.
Using the HP 8510 network analyzer to measure the radiation patterm of a dipole antenna using time domain and gating to remove the effects of ground clutter
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.
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