Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
2000-06-16
2002-05-14
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C359S290000
Reexamination Certificate
active
06388616
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of optically controlled phased array antenna/radar systems. More particularly, the present invention relates to a system for creating continuous true time delays in a photonic beam array system, which is used to produce a microwave beam array with the same time delays to control/steer the propagation direction of the phased array antennas.
2. Description of the Related Art
Phased array antenna systems are well known in the art. A phased array may be used to point a fixed radiation pattern or to scan rapidly in azimuth or elevation.
Such systems can be used, for example, in a tracking system for tracking objects of interest such as aircraft or missiles, and in a high data rate wireless mobile communication system.
In order to steer a microwave beam from a phased array antenna, it is necessary to create a time delay t between the electromagnetic waves generated from each of the neighboring antenna elements in a particular direction.
Traditionally, the time delay in a phased array antenna system has been made by a microwave electronic delay device or an electronic phase shifter (which is not even a true time delay device). However, given the large number of antenna array elements needed, it is necessary to use a large number of delay devices and waveguides (cables), making the overall system very bulky and expensive. Moreover, such systems yield poor quality results.
In the last ten years or so, there have been extensive efforts to develop an optically controlled phased array antenna, in which time delays are generated in the optical domain and then are carried over to the microwave domain using optical fibers. However, most of such proposed schemes have failed because of significant technical difficulties or very expensive material and assembly costs due to their system complexity.
Thus, there exists a need in the art for a simplified and inexpensive system for generating a true time delay in a phased antenna array system.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a simplified and inexpensive true time delay device for optical control of a phased array antenna system.
To this end, according to the present invention, there is provided a true time delay system for optical control of a phased array antenna including a first time delay unit having a pair of parallel end walls having mirrored surfaces facing each other in a zigzag pattern, and an intermediate wall which is substantially parallel to the end walls and has mirrored surfaces on both sides which match the end walls. The intermediate wall also has matching openings in the mirrored surfaces to permit light to pass through the intermediate wall. A displacement unit displaces the intermediate wall relative to the end walls to change the distance that a series of input light beams travels, creating a true time delay in a first dimension. A second time delay unit receives the output of the first time delay unit, provides a time delay in a second dimension and outputs light beams having a time delay in both the first and second dimensions.
More particularly, the present invention is directed to a true time delay generator for optical control of a phased array antenna system having an array of antenna elements arrayed in a first dimension and a second dimension and having a number n of antenna elements in the first dimension and a number m of antenna elements in the second dimension, the generator comprising:
(a) first time delay means for providing a time delay for optical control of the phased array antenna system in the first dimension, the first time delay means for guiding a set of input light beams corresponding to the number n of antenna elements in the first dimension to provide an output comprising a first series of light beams, N in the total number, delayed relative to one another with an equal amount of time delay in the first dimension between each two consecutive light beams of the first series of light beams;
(b) splitter means for splitting each light beam of the first series of light beams to provide an output comprising N groups of M light beams;
(c) second time delay means for providing a time delay for optical control of the phased array antenna in a second dimension, the second time delay means for guiding the output of splitter means to provide an output comprising the N groups of M light beams in which the M light beams in each group are delayed relative to one another to have an equal amount of time delay between each two consecutive light beams in each group in the second dimension, the N groups of light beams constituting signals for optoelectric conversion for steering a propagation direction of the phased array antenna;
wherein the first time delay means comprises a delay generator unit and the second time delay means comprises N delay generator units, each of the delay generator units comprising:
(i) first and second end walls disposed substantially parallel to each other and forming a cavity therebetween, the first end wall having a first plurality of mirrors formed thereon and the second end wall having a second plurality of mirrors formed thereon to face the first plurality of mirrors;
(ii) an intermediate wall disposed between the first and second end walls and being substantially parallel thereto to form a first chamber and a second chamber in the cavity, the intermediate wall having a third and a fourth plurality of mirrors formed on opposite sides thereof to face respectively the first plurality of mirrors of the first end wall and the second plurality of mirrors of the second end wall, the intermediate wall having a series of apertures for passage of the input light beams from the first chamber to the second chamber; and
(iii) displacement means, for example, a motor, for displacing one of (1) the intermediate wall relative to the first and second end walls and (2) the first and second end walls relative to the intermediate wall, so that an area of the first and second chambers is variable for changing a time delay of the optical path of the input light beams in the cavity.
The set of input light beams are input into the first chamber of the first delay means so as to impinge on one of the third mirrors of the intermediate wall of the first delay means and then to reflect between the third mirrors and the first mirrors of the first delay means before passing through the apertures of the first delay means into the second chamber of the first delay means and then to reflect between the fourth mirrors and the second mirrors of the first delay means before passing out of the second chamber of the first time delay means and to the splitter means and then to the N delay generator units of the second time delay means as the N groups of M light beams, and each of the N groups of M light beams are input into the first chamber of a respective one of the N delay generator units so as to impinge on one of the third mirrors of the intermediate wall of the respective one of the N delay generator units and then to reflect between the third mirrors and the first mirrors of the respective one of the N delay generator units before passing through the apertures of the respective one of the N delay generator units into the second chamber of the respective one of the N delay generator units and then to reflect between the fourth mirrors and the second mirrors of the respective one of the N delay generator units before passing out of the second chamber of the respective one of the N delay generator units.
The N delay generator units of the second time delay means may be vertically stacked such that all N first and second end walls are attached together rigidly, and all N intermediate walls are attached together and movable together by the displacement means. The true time delay generator may further comprise amplification means for amplifying the output of the first time delay means. The light source for providing the input light beams may be a light source array position
Clohan Paul
Issing Gregory C.
The United States of America as represented by the Secretary of
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