Communications: radio wave antennas – Antennas – Measuring signal energy
Reexamination Certificate
2002-11-04
2004-06-15
Nguyen, Hoang V. (Department: 2821)
Communications: radio wave antennas
Antennas
Measuring signal energy
Reexamination Certificate
active
06750822
ABSTRACT:
The present invention relates to an method and apparatus for the highly accurate characterization of radiation fields.
The evaluation of radiation fields is indispensable in many areas, as, for example, in antenna near-field measuring technology. In near-field measuring, which is preferably used for antennas in the frequency range from approximately 0.5 to 20 GHz, the immediate electromagnetic near field of an antenna is measured and is converted by means of a near-field (NF) to far-field (FF) transformation into the far field by means of the Fast Fourier Transformation (FFT). The advantage of measuring the near field of an antenna lies in the compact dimensions of the necessary antenna measuring systems, which heretofore have almost exclusively been integrated into stationary measuring chambers.
In contrast to near-field measuring systems, there are also far-field measuring systems. However, due to their dimensions, these are exterior systems, and are always stationary devices. also, they are considerably more prone to error as a result of reflections from the environment, terrain formations, buildings, etc.
Another advantage of the near-field measuring technique is that, as a result of a near-field recording, all far-field sections can be computed, while the once measured far-field sections are fixed and the antenna has to be measured again for additional far-field sections at a later point in time.
In accordance with the scanning theorem, the near field is scanned in <&lgr;/2 intervals, and the entirety of the electromagnetic radiation emitted by the antenna must be detected, down to approximately −45 db, because the totality of these measuring points has an influence on each individual computed far-field point.
For measuring the radiation fields of omnidirectional antennas, spherical scanners are usually used, which scan the near field of the antenna to be measured on a spherical surface. In the case of directional antennas, the high-expenditure spherical scanners may be eliminated, as long as all radiation fractions down to approximately −45 db can be detected on a cylinder surface or on a planar surface. Since directional antennas (parabolic antennas) are mainly used, for example, in telecommunications, the selection in this field usually leads to cylindrical near-field measuring systems or planar systems.
In the NF to FF transformation, in addition to the amplitude values of the individual measuring points, phase information is also used. Therefore, a scanner, , should be able to scan a spherical surface, a cylinder or a planar surface by means of a measuring probe as nearly ideally as possible, because the NF to FF transformation is mathematically based on this ideal case. Error contributions by the scanner of a near-field measuring system should not exceed a deviation of &lgr;/50 from the ideal contour.
Thus a scanner accuracy of 3.0 mm, at f=2.0 GHx and a phase accuracy of &lgr;/50 are necessary. If ground station antennas with an antenna diameter of, for example, 14 mm are to be measured by means of a planar measuring system, this degree of accuracy must be achieved on a surface of at least 20 m×20 m.
For use with radar systems, near-field scanners should be as invisible as possible. This is of course contrary to the normal mechanical structures required for such scanners, and as a rule can be achieved only by the use of corresponding absorber coverings.
In order to obtain a maximum of phase accuracy of the measurement, data recording should be recorded for of all measuring points as rapidly as possible in order to minimize temporal phase drifts as much as possible.
Based on the above-mentioned example, with a surface to be scanned of 20 m×20 m and a measuring point distance of 75 mm, an array of 267 measuring points in width and 267 measuring points in height of the antenna, results in a total of at least 71,289 measuring points. A rough estimate shows that it would require unacceptable expenditures to drive to each of the measuring points, so that measuring must take place during the drive while passing the measuring position. At a scanning speed of 100 mm/sec., data recording would therefore require approximately 15 hours.
From Stehle et al., “Reledop: A Full-Scale Antenna Pattern Measurement” L.E.E.E. Trans. On Broadcasting, Volume 34, No. 2, June 1988 (1988/06, Pages 210-220 YP 000054225 New York, US) and also Hen&bgr;, “Hubschrauber-Messung” NTZ Nachrichtentechnische Zeitschrift, Volum 40, No. 4, April 1987 (1987/04, Pages 258-261, YP-002168218) Berlin, Del.), it is known to arrange probes by means of a pilot-controlled helicopter with the interposition of a long trail rope or a telescopic rod in a field to be measured. The use of a real helicopter and the interposition of long trail ropes or telescopic rods, however, do no permit highly accurate measuring, and particularly no highly accurate positioning within the field to be measured.
It is an object of the present invention to provide an method and apparatus for a highly accurate evaluation of radiation fields, by means of which highly accurate and large-surface measurements of radiation fields can be carried out at relatively low expenditures, particularly in the exterior region.
This an other objects and advantages are achieved by the measuring arrangement (particularly a mobile measuring arrangement) for the alignment/position and/or detection of electromagnetic characteristics of devices for/with the] emission of radiation fields according to the invention, which includes a remotely-controllable measuring device that can hover, and has a measuring probe for detecting the targeted signal, as well as at least one device for determining the attitude and position of the measuring device.
For determination of the attitude and position, position determination systems are preferably arranged in the vicinity of the emission device, in the form of position receivers/antennas that are provided in a defined position relative to the hovering device.
In the measuring device according to the present invention, preferably a highly accurate global, non-terrestrial position determination system (such as the GPS) is used as the position determination system.
Furthermore, it is preferred that the position receiver/antenna of the system for measuring the site, the position and the attitude, is arranged on the measuring probe. In order that the electromagnetic measurement conform as accurately as possible to the position determination or alignment of the emitting device, the phase center of the measuring probe should be situated as close as possible to the position receiver/antenna.
Furthermore, the emission device is preferably an antenna and, more specifically, a parabolic antenna or an array antenna.
In addition, the measuring arrangement may be include a combination of the position receiver/antenna, a compass, a device for measuring inertia forces, and one or more rotation sensors for determining and controlling the attitude of the hovering device. To the extent that it may be necessary in a special application, other components can be added.
According to another feature of the measuring device has a plurality of spatially separated position receivers/antennas. This permits the use of a differential method for determining the position and attitude of the hovering device.
In a further embodiment of the measuring arrangement according to the invention, an additional position receiver/antenna is provided as a reference on the ground in the area of the emission device. This permits the use of a differential method for determining the position and attitude of the hovering device.
In a measuring arrangement constructed in this manner, direct visual contact is not required between a ground station (at which, for example, the measuring equipment for processing the data supplied by the measuring probe, as well as devices for controlling the hovering measuring device can be provided) and the receiver. This may be an advantage, particularly in the case of spherical scanning contours.
The pos
Astrium GmbH
Crowell & Moring LLP
Nguyen Hoang V.
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