Communications: radio wave antennas – Antennas – Measuring signal energy
Reexamination Certificate
1999-09-27
2001-02-20
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Measuring signal energy
C343S766000, C343S765000, C342S360000
Reexamination Certificate
active
06191744
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable
BACKGROUND—FIELD OF INVENTION
This invention relates to a probe movement system for spherical near-field antenna testing.
BACKGROUND—DESCRIPTION OF PRIOR ART
Near-field testing of an antenna is a technique that calculates the far-field antenna pattern from multiple radio frequency (RF) measurements taken very close to the antenna. The far-field antenna pattern is of vital concern to a system that uses an antenna. The far-field pattern details the direction and shape of the antenna main beam and the sidelobes. Sidelobes show where and how much an antenna will pick up or send signals outside of the main beam. Designers normally try to make sidelobes as small as possible. Near-field testing has several advantages over direct far-field testing. Near-field results are usually more accurate due to better control of reflections. Near-field testing can usually be done indoors in controlled conditions. The data from near-field testing can be manipulated (back transformed) to find malfunctioning elements in an array antenna.
In near-field testing a probe (a small antenna) is moved over a plane in front of the antenna or over a cylindrical or spherical surface enclosing the antenna. The probe emits or receives RF to or from the antenna. The amplitude and phase of the received RF signal is recorded at specific and equally spaced probe locations. A computer program manipulates this data and predicts the far-field pattern. The increasing power of digital computers has made the near-field technique much easier and faster to use.
In most spherical near-field antenna testing two orthogonal axes describe probe movement over the spherical surface. The axes are usually called azimuth and elevation or phi and theta. For high accuracy the two axes must be close to 90°, the probe must at a constant radius, and the probe position must be accurately known. In most spherical near-field antenna testing the antenna is rotated in at least one axis to cause an effective probe movement over the spherical surface.
An exception to moving the antenna is a double gantry arm design shown on page 168 of “Spherical Near-Field Antenna Measurements” edited by J. E. Hansen Published by Peter Peregrinus LTD, London, United Kingdom 1988. The probe is moved in two axes by a double gantry arm with the antenna held stationary on a nearby post. The upper (elevation) arm which moves the probe in elevation is not counterweighted therefore movement of the arm requires more torque and power. Also, movement of the arm causes changing stress and strain in the supporting azimuth arm and base resulting in errors in the probe location. The lower (azimuth) arm which moves the probe and elevation arm in azimuth is not counterweighted therefore movement of the azimuth arm causes changing stress and strain in the supporting base resulting in errors in the probe location. The antenna support post limits the rotation of the lower azimuth arm. This post limits the area where the far-field pattern can be calculated and/or increase errors due to increased RF reflection into the antenna or probe.
There are several U.S. patents that discuss obtaining far-field patterns from near-field data without any discussion how a probe is moved. These patents are: U.S. Pat. Nos. 3,166,748 to Shanks et al., 3,879,733 to Hansen et al., 4,553,145 to Evans, 5,270,723 to Lopez et al., 5,410,319 to Lopez et al., 5,432,523 to Simmers
Several other U.S. patents discuss specific probe movement in near-field testing. These patents require some movement of the antenna or are not spherical near-field antenna testing with the antenna inside the sphere. These patents are:
U.S. Pat. No. 4,201,987 to Tricoles and Rope discusses spherical near-field techniques. The patent does discuss probe movement. The probe is moved over a circular path by two orthogonal linear movements (a vertical post and extending arm). The probe is simultaneously rotated to continuously point at the center of a sphere. The antenna is rotated to provide the other axis of movement
U.S. Pat. No. 4,453,164 to Patton discusses the use of near-field data. The only type of probe movement discussed is planar.
U.S. Pat. No. 4,661,820 to Pouit et al. discusses obtaining far-field pattern from near-field data. The patent discusses rotating the antenna in azimuth and optionally in elevation. If the antenna doesn't move in elevation the probe does, otherwise the probe is fixed.
U.S. Pat. No. 4,704,614 to Poirier et al. discusses obtaining far-field pattern from near-field data. The patent does discuss probe movement. The method used is a type of distorted planner near-field. The antenna under test is stationary and faces upward. A Foucault pendulum is positioned over the antenna and a probe is attached to the end of the pendulum. The pendulum is swung and the Earth's rotation causes the pendulum swing direction to rotate over the face of the antenna. The probe path describes a sphere segment. The amount of far-field patterns that can be obtained is limited because the antenna is external to the sphere.
U.S. Pat. No. 5,365,241 to Williams discusses planar near-field techniques. This patent does discuss probe movement. The probe moves over a planar surface swinging on an arm while the antenna is rotated underneath.
SUMMARY
A probe movement apparatus for spherical near-field antenna testing that moves a probe over a spherical measurement surface or path by two bent cantilevered (gantry) arms. The antenna under test is located within the spherical surface and can be held stationary during testing.
Objects and Advantages
Accordingly, besides the objects and advantages of the probe movement system described in my above patent, several objects and advantages of the present invention are:
(a) to perform spherical near-field testing while keeping the antenna stationary this prevents movement or twisting of waveguide and cables connected to the antenna which increases test accuracy;
(b) the antenna can be tested in it's normal orientation which improves accuracy when gravity or thermal loads are significant;
(c) deflections in the base portion effect both the antenna position and probe position equally, this improves accuracy, and allows a less rigid, cheaper, and more portable base;
(d) the antenna may be rotated slightly to check for or minimize RF reflections increasing accuracy;
(e) the counterweight on the elevation arm improves accuracy by eliminating changing stress and strain on the azimuth arm as the elevation arm moves;
(f) the freedom to rotate the azimuth arm through 360° allows the azimuth arm two possible positions for each probe position this can be used to minimize RF reflections increasing accuracy.
Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.
REFERENCES:
patent: 3166748 (1965-01-01), Shanks et al.
patent: 3879733 (1975-04-01), Hansen et al.
patent: 4201987 (1980-05-01), Tricoles et al.
patent: 4453164 (1984-06-01), Patton
patent: 4553145 (1985-11-01), Evans
patent: 4661820 (1987-04-01), Pouit et al.
patent: 4704614 (1987-11-01), Poirier et al.
patent: 5270723 (1993-12-01), Lopez et al.
patent: 5365241 (1994-11-01), Williams et al.
patent: 5410319 (1995-04-01), Lopez et al.
patent: 5432523 (1995-07-01), Simmers et al.
patent: 5473335 (1995-12-01), Tines
patent: 5485158 (1996-01-01), Mailloux et al.
patent: 5999139 (1999-12-01), Benjamin et al.
patent: 6023247 (2000-02-01), Rodeffer
“Spherical Near-Field Antenna Measurements” (p. 168) Ed by J.E. Hansen, PUB. Peter Peregrinus LTD, London UK 1988.
Snow Jeffrey
Thompson Kenneth
Ho Tan
Vo Tuyet T.
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