Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Statutory Invention Registration
2002-04-03
2004-09-07
Pihulic, Daniel T. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S373000, C342S443000, C342S444000, C342S445000, C342S196000, C342S020000
Statutory Invention Registration
active
H0002109
ABSTRACT:
BACKGROUND OF THE INVENTION
When a military aircraft flying in unknown or hostile air space is discovered by a distant radar apparatus it is often beneficial for the crew of the aircraft to not only be made aware of the occurrence of this radar discovery but to also be appraised of as much information regarding the discovering radar as is possible. Two significant portions of this discovering radar information are the physical location of and the operating frequency of the distant radar apparatus. In addition to the fundamental act of receiving such information concerning the discovering radar apparatus it is desirable that this information become available to the aircraft crew as quickly as is possible and that the information be obtained from as little as one pulse of energy received from a threat signal source. The obtaining of this and other information such as pulse duration and signal strength data in a passive non-signal radiating manner from a distant threat signal is the role of the electronic warfare radio receiver.
The radio receiver arrangement we have identified by the name of a “monobit receiver” offers an attractive basis for fabricating such an electronic warfare receiver and for solving several problems arising in the electronic warfare and other military electronics fields of endeavor. One group of such problems is locating the source of a distant radio frequency emission from a single pulse of received radio frequency energy emission i.e., providing a radio frequency direction finding capability that is usable in the present day passive monopulse electronic signal environment. Although radio receivers technically capable of performing in this direction finding and frequency identification environment have existed for some time the cost, technical complexity and physical size of each such existing receivers and related problems such as relatively short intervals of mean time between receiver failure events have limited the practicality of direction finding apparatus using existing electronic warfare receivers. This limitation is especially notable with respect to locating such apparatus within the confines of and within the weight limitations of a host aircraft such as a tactical or fighter aircraft.
It has been clear to persons working in the monopulse systems technical field that a passive instantaneous direction finding apparatus built around a multiple element directive antenna having elements coupled through a phase responsive network such as a Butler matrix to a plurality of individual radio receivers would be within the realm of technical possibility except for the penalty of cost, technical complexity and physical size associated with each of the individual radio receivers needed to embody such a system. Indeed persons working in this field have proposed such direction finding and frequency identification systems in considerable detail. One such system is for example disclosed in the 1996 U.S. Pat. No. 5,568,154 of Yakov Cohen of Haifa, Israel. The Cohen '154 patent indeed involves a frequency and direction finding system inclusive of a multiple element directional antenna, a Butler matrix and radio receivers assembled into a combination providing first blush similarity to the system of the present invention.
A more detailed consideration of the Cohen direction finding and frequency identification system reveals however the use of several radio receivers of one of the types identified as “channelized receivers, Bragg cell receivers, compressive receivers (and) digital FFT receivers”, see column 1, line 19 of the Cohen patent. Five of a selected one of such receiver types are included at 122-130 of the Cohen patent's exemplary FIG. 1 direction finding system drawing. When the cost, technical complexity and physical size associated with each of these previous receiver types is considered, the limited utility of the resulting Cohen FIG. 1 system, particularly in a small aircraft, begins to emerge however. The inventors of the present invention have used receivers of these previous types in experimental laboratory work and in fact one of the present inventors has authored a published text book in which both technical characteristics and physical embodiment photographs of individual receivers of this type appear. See the Text “Microwave Receivers With Electronic Warfare Applications” authored by James Bao-Yen Tsui, published by John Wiley and Sons, copyright 1986. Photographs of circa mid 1980's versions of receivers of these channelized receivers, Bragg cell receivers, compressive receivers and digital FFT receiver types appear on pages 229, 330, 279 and 183 respectively in the Tsui text. From these photographs the physicalsize portion of the difficulties attending a system according to the Cohen patent, using five or more of such receivers, becomes apparent. In the interest of simplifying and shortening the present document nevertheless the contents of both the Cohen patent and the Tsui text are hereby incorporated by reference herein. At the very least these documents provide enlightening background and signal characteristics information. Another text providing helpful background information with respect to the present invention is the text “Microwave Passive Direction Finding” authored by Stephen E. Lipsky, also published by John Wiley and Sons, and copyright 1987. The Lipsky text is also hereby incorporated by reference herein.
A significant part of the difficulty with the previous digital FFT receivers heretofore potentially used in monopulse frequency and direction-finding applications relates to the algorithm used to embody the Fourier transformation operation in the receiver. Most Fourier transformation realizations necessarily include an extensive use of numeric multiplication in computing values related to the kernel function portion,
ⅇ
-
j2
π
kn
N
,
i.e., the exponential of “e” the base of the natural logarithm, within the Fourier transformation algorithm. Both the number of and the size of each individual of these multiplications contributes to the complexity of rigorously implementing the Fourier transformation in either hardware or software form and especially to the difficulty of implementing this operation in real time. In an effort to reduce this complexity one of the present invention inventors, James B.Y. Tsui and a number of colleagues, have shown that Fourier transformation Kernel functions of unit magnitude or substantially unit magnitude may be used to successfully approximate a true Kernel function value and enable the realization of a Fourier transformation using only multiplication by unity or in essence no multiplication in the Fourier transformation computation algorithm. Kernel function realization in this manner is disclosed in a first U.S. Patent of Tsui et al., a patent numbered U.S. Pat. No. 5,917,737, wherein Kernel function values are located on a circle of unit radius at angular locations of &pgr;/4, 3&pgr;/4, 5&pgr;/4 and 7&pgr;/4 radians.
A later patent document involving inventor Tsui and colleagues wherein the Kernel function values are moved on the circle of unit radius to locations of 0, &pgr;2, &pgr;, and 3&pgr;/2 radians is identified as U.S. Pat. No. 5,963,164. In a yet later patent document, the U.S. patent application identified with Ser. No. 09/944,616 and filed on Sep. 4, 2001, inventor Tsui and a colleague have demonstrated advantages available when Kernel function values located at each of the &pgr;/4, 3&pgr;/4, 5&pgr;/4 and 7&pgr;/4 radian locations are added to the Kernel function values at 0, &pgr;/2, &pgr;, and 3&pgr;/2 radians with the added four values being slightly increased in magnitude from unit circle values and in fact having a magnitude of (2)
1/2
or 1.414.
The incentive for improving the Kernel function approximations over that of the earlier U.S. Pat. No. 5,917,737 patent is ease of realizing the approximation in the transition of the U.S. Pat. No. 5,917,737 patent to that of the U.S. Pat. No. 5,963,164 patent and a desire for improv
Graves Keith M.
Tsui James B. Y.
Hollins Gerald B .
Kundert Thomas L.
Pihulic Daniel T.
The United States of America as represented by the Secretary of
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