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Far field antenna radiation patterns of vehicle mounted antennas are often recorded on the antenna range by rotating the entire vehicle/antenna system with a multiple axis vehicle positioner. Antenna patterns, obtained in this manner, consider the antenna and vehicle as a system and include the effects of the vehicle structure. These patterns are more representative of the operational antenna patterns than the “free space” patterns of the antenna itself. When the antenna is arbitrarily directed on the vehicle, standard antenna pattern cut trajectories, recorded in the coordinate system of the vehicle, become skewed when referenced to the coordinate system of the antenna. With proper adjustment of the fixed angles of the vehicle positioner however, selected standard antenna pattern cut trajectories, referenced to the antenna, may be obtained. The required fixed vehicle positioner angles are obtained from solutions to systems of equations representing the coordinate transformations for the positioner/vehicle/antenna system. In this paper, two general methods of obtaining the coordinate transformation equations are reviewed. These equations are then solved to obtain expressions for the positioner angles necessary for specific cut trajectories. A practical example of a six axis transformation associated with measurements of a three axis gimballed aircraft mounted radar antenna and a three axis vehicle positioner is used to illustrate the techniques (This example was taken from a recent RADC/Newport measurement program.
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.
This paper presents a method for determining the measurement cone associated with the measurement of far field antenna pattern using a multiaxis positioner. Using the Piogram, a convenient method for specifying the transformation matrix between two rotating coordinate systems, it is shown how to determine the transformation matrix for any general multiaxis positioner. Given the transformation matrix, the parameters of the measurement cone are then derived in a straightforward manner, which is summerized [sic] by a step by step procedure.
A cylindrical near-field antenna range has been designed, implemented and tested recently at the Cobb County Research Facility of Georgia Tech’s Engineering Experiment Station. While Georgia Tech has had an operational planar scanner since 1974 [1], the relocation of a portion of the Experiment Station to an off-campus site, together with the need for measurements of antennas not practical with the existing planar scanner, prompted the addition of a cylindrical near-field range. Provision was made in the range instrumentation for planar-polar and spherical near-field measurements. Computer software was written to effect the conversion from cylindrical near-field measurements to far-field patterns.
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.
At a time of increased interest in computer-controlled antenna test ranges, it is worthwhile to consider the advantages, problems, and consequences inherent in the practical application of automated measurement techniques. This paper describes some of TRW’s experiences with the utilization of an automated far-field antenna test range to measure the characteristics of a Ku-band monopulse cassegrain spacecraft antenna. It also includes several conclusions drawn from those experiences.
Near-field antenna measurement techniques offer an alternative to conventional far-field antenna measurement techniques. Of the various coordinate systems used for near-field measurements, the spherical coordinate system provides the most natural extension from the conventional far-field characterization of an antenna to a more general characterization for arbitrary range lengths. This paper describes the Scientific-Atlanta Model 2022, a user-oriented implementation of a spherical near-field antenna measurement system. An example of typical system usage is provided. System capabilities and performance are described. Key concepts required to understand and use the spherical near-field method are discussed. The advantages and disadvantages of near-field antenna testing in relation to conventional far-field testing are considered. The particular merits of spherical near-field testing as compared to other forms of near-field testing are discussed. Antenna testing situations which provide the most likely candidates for the spherical near-field measurement technique are described.
The Naval Air Engineering Center has been assigned the task of developing Near Field Measurement Techniques and Equipment for testing Navy Aircraft-mounted antennas. These efforts will be applied to Nose-mounted and Wing-mounted antennas. The ultimate objective is the development of a portable near-field test system for the Navy’s ‘O’ level. The test system will produce far field pattern predictions of installed airborne antennas by measuring and processing near field data. NAEC would, also, like the test system to determine if an installed antenna is mission capable or degraded; and in the event of a failed antenna, the test system will isolate the fault of that antenna. This paper will describe NAEC’s progress in this task by descriptions of the following: I. Electrical Hardware i.e. transmitter, receiver, interfaces, controllers II. Mechanical Hardware i.e. translator, probe carriage III. Mathematical approaches Also, recent laboratory results will be described.
The compact antenna range has been recognized as an effective means of testing microwave antennas. Antennas which normally require long outdoor ranges for testing can be tested under far field conditions at an indoor facility, using the compact range. The compact range operates on the principal that a parabolic reflector will transform an incident spherical wave into a collimated plane wave in its near zone. The plane wave produced is suitable for testing antennas, thus simulating far field electromagnetic criteria in the near zone. The typical compact range is housed in a room approximately 20 feet wide, 40 feet long and 20 feet high. The performance of the compact range has been well documented and specified over a frequency range of 3.95 GHz to 18.0 GHz. Now, through recent testing performed at Scientific-Atlanta, the compact range can be specified for operation up through 60.0 GHz. This paper describes the tests that were performed, discussed the results of these tests and establishes performance specifications for operation at these millimeter frequency bands.
This paper describes a new, automated, microprocessor controlled, dual-channel microwave vector ratio measurement receiver for the frequency range 10 MHz to 18 GHz. It provides a greater than 120 dB dynamic range and resolutions of 0.001 dB and 0.1 degree. Primarily designed as an attenuator and Signal Generator Calibrator, it offers solutions to antenna measurement problems where high accuracies and/or wide dynamic measurement ranges are required such as for broadband cross-polarization measurements on radar tracking antennas, highly accurate gain measurements on low-loss reflector antennas, frequency domain characteristics measurements on wide-band antennas with resulting data suitable for on-line computer conversion to time domain transient response and dispersion characteristics data and wideband near field scanning measurements for computing far field performances. The measurement data in the instrument is obtained in digital form and available over an IEEE-488 bus interface to an outside computer. Measurement times are automatically optimized by the built-in microprocessor with respect to signal/noise ratio errors in response to the measurement signal level and the chosen resolution. Complete digital measurement data amplitude of both channels and phase, is updated every 5 milliseconds.
Digital signal processing techniques provide a method by which a finely resolved antenna pattern can be reconstructed from coarsly sampled data. Antenna pattern reconstruction offers several advantages over the direct measurement of a finely resolved pattern, and is applicable whenever a computer is available for implementation of the reconstruction algorithm. As computerized pattern measurement equipment becomes more prevalent, pattern reconstruction algorithms will become more common place. The advantages of pattern reconstruction include higher quality presentation of antenna patterns due to increased resolution, decreased data acquisition time due to coarser sampling, and decreased data storage requirements. The mean square error or a reconstructed antenna pattern is smaller than that of the directly measured pattern. In the context of near-field to far-field pattern transformations, pattern reconstruction becomes essential. The transformation is performed at a coarse spacing for maximum computational speed without compromising the quality of output data. This paper provides an introduction to the technique of antenna pattern reconstruction. Key concepts and terminology are discussed A generic reconstruction algorithm is developed. Examples of interpolated antenna patterns are shown.
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.