Communications: radio wave antennas – Antennas – Measuring signal energy
Reexamination Certificate
1999-02-04
2001-09-04
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Measuring signal energy
C342S360000
Reexamination Certificate
active
06285330
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to mechanically rotating surface based antennas, and more particularly to the efficient near field testing of such antennas.
BACKGROUND OF THE INVENTION
Rotating surface based antennas can be parabolic, flat plate arrays or pleased arrays (or any other arbitrary shaped antennas) which can be steered electronically in elevation. The latter two types of antennas are characterized by an array of radiating elements and an elaborate network of power distribution components. It is very difficult to diagnose these antennas, especially in field conditions, and after years of operational use. Ordinarily, modern systems include automatic on-line testing that tests most of the prime components but does not usually test the radiating elements. Any known radiating element testing which may be provided is either quite crude and does not provide accurate and high resolution fault detection and isolation, or it is very difficult to perform, especially in field conditions.
Known prior techniques for providing field diagnosis of the radiating elements of the antenna include near field probing and far field pattern measurement. Near field probing requires that the antenna be stopped from rotating and that a probe sample the near field across the whole aperture. This techniques requires the construction of scaffolds and precise probe guide fixtures around the antenna. As a result, operational use of the antenna is stopped for a period which may last for several days. Other known near field techniques require that the test probe be moved in a circular path near the array, requiring a complex and highly accurate mechanical apparatus. Such near field testers are expensive.
Far field tests include placement of a radiating element in the far field and performing radiation pattern measurements. These techniques are elaborate logistically, as they require another site with line of sight to the antenna, and higher power for the test signal due to the greater distance. In addition, multi-path signals are also usually present which contaminate the test results.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to overcome the problems of the prior art described above by providing the capability of fault detecting and isolating a complete antenna without requiring construction of an elaborate test fixture around the antenna.
It is a further object of the present invention to provide an apparatus and a method for fault detecting and isolating a complete antenna without the power requirements and multi-path contamination of a far field measurement apparatus and method.
It is still further object of the present invention to provide an apparatus and a method for fault detecting and isolating a complete antenna which considerably cuts the cost and downtime for such testing.
Therefore, and according to a preferred embodiment of the invention, a stationary RF probe is located at a fixed arbitrary, but known point in the near field of the antenna under test. This configuration (one of several possible configurations) is suitable for testing a mechanically rotating antenna, with electronic beam-steering capability in elevation. An RF signal is transmitted from the probe to the array, and the signal from the antenna is coherently down converted and stored in the apparatus. The antenna mechanically rotates, and the phase shifter of the row under test is toggled, typically between 0 and 180 degrees. In each phase state coherent data is sampled, digitized, and stored while all other phase shifters remain fixed. After one revolution, data collection for that row is complete. The phase shifter of the next row is then toggled and the above cycle is repeated. Full data collection requires a number of scans equal to the number of rows. Operational activity of the antenna can resume immediately after the data collection cycle is complete. Analysis of the stored data is then performed. By subtracting stored vectors of two adjacent stored samples, all rows but the one with the toggled phase shifters are removed. The data from the isolated row is then used by an imaging algorithm which maps the complex excitation function of that row. This process will be referred to later as MTI (Moving Target Indicator) process.
According to a second embodiment of the apparatus, a moving probe is located in the near field of the antenna under test. This configuration is suitable for testing a mechanically rotating antenna without electronic steering capability. The probe is moved vertically in an arbitrary, but known set of paths, by a predetermined increment. In each location, coherent data is collected for an entire scan. The data collection is complete when the probe is scanned thorough all the vertical positions. For each position, coherent data is collected for the complete revolution. The data collection cycle will require a number of scans equal to the number of vertical positions of the probe. Although this embodiment requires a mechanical apparatus for the vertical motion of the probe, this apparatus is not restricted to a particular path and thus can be manufactured at a much lower cost with fewer restrictions on installation and use.
Therefore, the described apparatus and method can map one dimensional excitation (collapsed) in a specific cut of any antenna (parabolic, phase array, etc) typically, in one revolution thereof, and two dimensional excitation in several revolutions as previously discussed.
Other objects, features and advantages of the present invention will become apparent from the following Detailed Description of the Invention as read in conjunction with the accompanying drawings.
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Sensis Corporation
Wall Marjama & Bilinski
Wimer Michael C.
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