Communications: radio wave antennas – Antennas – Measuring signal energy
Reexamination Certificate
2000-05-24
2001-01-30
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Measuring signal energy
C343S765000, C342S360000
Reexamination Certificate
active
06181285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to antenna radiation pattern measuring equipment and more particularly to low-distortion positioning equipment for antenna radiation pattern measurements.
2. Description of the Related Art
To completely characterize an antenna radiation pattern—especially for antennas having low gain and broad beamwidth—the gain must be measured over the entire 4&pgr; steradians solid angle. There are three ways to accomplish this goal. One way is to hold the antenna under test (AUT) in place and move the probe antenna along the surface of an imaginary sphere at a fixed radius from the AUT. The apparatus used to move the probe antenna is usually unwieldy and causes unwanted scattering which distorts the AUT radiation pattern.
A second way to accomplish the goal is to hold the probe antenna stationary and rotate the AUT such that the probe antenna appears to move along the imaginary sphere with respect to the AUT. The AUT orientation is changed at a fixed point thereby reducing the size and complexity of the positioning equipment compared to the first way. This is probably the most usual configuration. The positioning equipment once again causes undesired scattering that distorts the radiation pattern of the AUT.
The third way to accomplish the goal is to combine the previous two techniques. Usually the AUT is rotated azimuthally while the probe antenna is moved along an arc above the AUT. The concept is simpler than either of the two previous techniques, but the distortion caused by the positioning equipment is usually significant. To reduce the complexity of the arc and the azimuth rotator, the arc is usually incomplete—a portion of the radiation pattern is purposely excluded from the measurement. Depending on the shape of the radiation pattern, this can be a serious problem.
SUMMARY OF THE INVENTION
The present invention relates to a novel technique for measuring the radiation pattern of an antenna along the entire sphere of an AUT while causing a minimal amount of distortion. The present invention utilizes what is known as a roll-over-azimuth positioner. The roll-axis is incrementally changed between successive rotations of the azimuth positioner. Two unique aspects of the invention are responsible for minimizing the distortion. Instead of placing the roll-axis mechanism atop the azimuth rotator, as is usually the case, the rotation of the roll-axis is accomplished through a connecting rod that can be inserted through an opening made in the back wall of the anechoic chamber. The mechanism is placed on the slide in such a way that the rod can be moved into the chamber, connect to the roll-axis shaft, rotate the roll-axis shaft incrementally, and withdraw from the chamber. The roll-axis mechanism therefore does not cause reflections inside the anechoic chamber while the measurements are collected along the azimuth axis. The other unique aspect of the present invention is the use of low dielectric material to support the AUT and the roll-axis. The low dielectric material minimizes the distortion usually caused by the AUT support and the roll-axis support.
It is therefore a principal object of the invention to provide low-distortion positioning equipment for antenna radiation pattern measurements.
A further object of the invention is to provide equipment of the type described wherein the rotation of the roll-axis is accomplished through a connecting rod that may be inserted through an opening made in the back wall of an anechoic chamber.
Yet another object of the invention is to provide a roll-axis mechanism which does not cause reflections inside the anechoic chamber while the measurements are collected along the azimuth axis.
Still another object of the invention is to provide equipment of the type described which utilizes low dielectric material to support the antenna under test and the roll-axis.
These and other objects will be apparent to those skilled in the art.
REFERENCES:
patent: 4968983 (1990-11-01), Maeda
patent: 5001494 (1991-03-01), Dorman et al.
patent: 5119105 (1992-06-01), Ngai et al.
patent: 5300939 (1994-04-01), Maeda et al.
patent: 6031498 (2000-02-01), Issler
Sullivan Jonathan L.
Winter James Blake
Centurion International, Inc.
Phan Tho
Thomte Dennis L.
Zarley McKee Thomte Voorhees & Sease
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