Economy of Near-Field Antenna Measurements

Authors: Gerald Hickman
Publication: AMTA 1979
Copyright Owner: NSI-MI Technologies

Near field antenna measurements have long been of interest to the antenna community and of particular interest to those in the design and measurement of antennas. Efforts in this area using analog computers for data reduction were already under way in the late 19SO's. These applications were limited, primarily due to the limitations of the analog computer. Two planar near field probe positioners were built by Scientific-Atlanta during this period and delivered; one to Martin Denver and one to the Georgia Institute of Technology. These units were used for development on planar near field measurements. The unit at Martin Denver .was-also used by the Bureau oL Standards. ExperimentaLwork at Georgia Tech led to Dr. Joy's thesis on spacial sampling and filtering.1 This work on sampling was· particularly important because it gave an understanding of the required data density for meaningful transformation by digital computer. Numerical integration is a time and core intensive process and it was the utilization of the Fast Fourier Transform in the early 1970 1 s that made the digital computer a viable approach to the problem.

 

Scientific-Atlanta Series 1580 Antenna Pattern Recorder

Authors: Sidney J. Manning, Samuel D. Davis
Publication: AMTA 1979
Copyright Owner: NSI-MI Technologies

Antenna pattern recorders are used to plot the relative signal strength of an antenna under test as a function of the angular position of the antenna. The signal plotted is obtained from the output of a receiver or directly from a microwave detector. The position information is normally obtained from synchro transmitters geared to the test posi ti oner axis. Typical antenna pattern recorders are electromechanical devices which employ servo systems to drive the recorder axis. A chart drive servo system positions the recording paper as a function of the angular position of the antenna. A pen servo system positions a recording pen in response to the amplitude of the input signal.

 

Conceptual Analysis of Measurement on Compact Ranges

Authors: Doren W. Hess, Richard C. Johnson
Publication: 1979 Antenna Applications Symposium
Copyright Owner: NSI-MI Technologies

The testing of microwave antennas or the measurement of radar backscatter usually requires that the antenna or target under test be illuminated by a uniform plane electromagnetic wave; however, the creation of such a wave is difficult. In practice, a uniform plane wave is approximated.

The conventional procedure for approximating a uniform plane wave is to locate a transmitting source antenna at such a distance that the incident wave can be considered to be planar. When the source antenna is located 2D2/λ away from the test antenna (where D is the largest dimension of the test antenna aperture and λ is the wavelength), the spherical wavefront emitted from the source will produce a maximum phase taper of ϖ/8 at the edge of the test antenna aperture. For most applications, such a phase taper is acceptable.

In a compact range [1-5], on the other hand, the incident plane wave is created by a range reflector and feed in the immediate vicinity of the test antenna. The basic principle of operation is illustrated in Figure 1. The diverging rays from the point-source feed are collimated by the range reflector, and a plane wave is incident on the test antenna or target. The incident wave has a very flat phase front but the feed-reflector combination introduces a small (but acceptable) amplitude taper across the test zone.

The principal advantage of a compact range is its small size; this allows it to be indoors and free from adverse weather effects. In research and development laboratories, a compact range can be located convenient to the design engineers. In manufacturing or rework facilities, a compact range can be located near an assembly line for use in final testing and adjustment. By placing the range in a shielded room, one can eliminate interference from external sources and provide a test site that is secured against monitoring by outside parties.

 

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