Communications: directive radio wave systems and devices (e.g. – Testing or calibrating of radar system
Reexamination Certificate
1997-12-09
2001-06-26
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Testing or calibrating of radar system
C342S004000, C342S001000
Reexamination Certificate
active
06252541
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to radar testing apparatus and, more particularly, to novel low radar cross section test mounts used to hold parts undergoing radar exposure in a radar cross section testing apparatus.
BACKGROUND
The development of stealth radar techniques requires measurement of any newly developed stealth object, such as a missile, vehicle or airplane wing, to determine the object's design effectiveness in minimizing reflection of incident radar energy. Those measurements are customarily made on radar cross section ranges. Such ranges basically consist of a test radar that sends radar signals to a remotely positioned test target, the stealth object, and receives and measures any returned radar echo, as may be reflected from the object.
Typically the test target is supported upon an RCS test mount and is continuously exposed to the radar signals. The mount slowly rotates the stealth object through 360 degrees while the test radar continuously measures the radar cross section. An ultimate goal, perhaps unattainable, of stealth design procedure is for the stealth object to avoid reflecting any echo whatsoever. As progress toward that end is made, a problem caused by the test mount arises.
When the radar cross section of the stealth object is very low, the mount used to support the stealth object during the test may have a larger cross section than the stealth object. Such a consequence may result even when the test mount is fabricated of an electrically non-conducting material, such as a dielectric. To the present none of the testing apparatus has means to permit one to distinguish between the echo from the target object and the echo from the test mount. This dilemma becomes more acute as stealth design techniques are improved and very low cross section targets are presented for measurement.
Several kinds of test mounts are found in present use. Steel mounts, resembling a knife blade in shape, are used for heavy test targets. The knife edge points toward the radar and is stationary. A motor, located at the top of the mount, rotates the test target. As might be expected, that kind of test mount does not have a low cross section.
Other mounts, available in many shapes, are fabricated of foamed plastic, particularly a material having a small dielectric constant and low reflectivity. These foam mounts also do not have a very low radar cross section. A motor below the surface of the ground rotates both the mount and the test target. For very low cross section test targets, the test target is suspended from a super structure by plastic strings, much like that for suspending a puppet. The super structure, however, is very inconvenient. Moreover, it is very difficult to control the orientation of the test target with the latter mount.
An object of the present invention therefore is to provide a very low radar cross section test mount for radar test ranges. Another object of the invention is to provide a very low radar cross section test mount that is relatively easy to use and is of a relatively simple structure.
SUMMARY OF THE INVENTION
In accordance with the present invention low radar cross section test mounts are attained in several alternate embodiments. In a first embodiment the test mount is fabricated of a dielectric material that is of a dielectric constant, &egr;, and a magnetic permeability characteristic, &mgr;, such that &egr; is essentially equal to &mgr;. In other words, the ratio of &egr; to &mgr; is essentially one. In a second embodiment, the test mount is a right circular cylinder of approximate diameter 0.61 wavelengths of the radar frequency and is constructed from a dielectric having a very low &egr;. In a third embodiment, a novel frequency transposing shield system is interposed between the radar transmitter and the test mount, whereby reflections or echoes occur displaced in frequency from that of the radar transmitter enabling the echo from the object under test to be distinguished from that reflected by its supporting test mount.
The foregoing and additional objects an advantages of the invention together with the structure characteristic thereof, which was only briefly summarized in the foregoing passages, becomes more apparent to those skilled in the art upon reading the detailed description of a preferred embodiment, which follows in this specification, taken together with the illustration thereof presented in the accompanying drawings.
REFERENCES:
patent: 4725490 (1988-02-01), Goldberg
patent: 4879560 (1989-11-01), McHenry
patent: 4990923 (1991-02-01), Delfeld
patent: 5229773 (1993-07-01), Danwen et al.
patent: 141598 (1947-11-01), None
Condon, Handbook of Physics, pp. I-54 to L-56 and p. 6 of Index.
Alston & Bird LLP
McDonnell Douglas Corporation
Sotomayor John B.
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