Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1998-11-18
2001-03-27
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S371000, C342S374000
Reexamination Certificate
active
06208293
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to phased array antennas, and more particularly to antenna elements that are formed of photo-conductive materials which when illuminated become conductive so that they are enabled to function as a receiving and radiating element.
BACKGROUND OF THE INVENTION
In the prior art, photo-conductive antennas activated by laser pulses are known. The antenna elements are fabricated from a photo-conductive semiconductor material that becomes conductive when illuminated by a light source, such as a laser, and thus can serve as a metal-like electromagnetic radiator/receiver. When the laser source is turned off, the photo-conductive antenna elements becomes non-conductive. In the non-conductive state the antenna elements cannot transmit or receive electromagnetic waves. In this non-conductive state the antenna elements gives no interference to nearby active antenna elements and are also immune from electromagnetic detection.
To achieve multi-octave frequency coverage with a phased array antenna, multiple layers of planar antenna elements, with each layer dedicated to an octave bandwidth, have been taught to circumvent the problems associated with each antenna element having to cover the entire frequency spectrum. To prevent the formation of extraneous grating lobes at the highest frequency of antenna array operation, the radiating elements must be closely spaced. This restricts the physical size of the antenna array, and the apparatus for optically illuminating the photo-conductive, semiconductor, antenna elements, which in-turn limits its performance at the lower frequencies of operation.
These designs, however, are based on conventional metallic conductor elements and the interaction between the layers proves detrimental to performance. Array designs have also been taught which place portions of metallic conductors on a substrate and interconnect these portions to form a dipole or patch radiator resonant at the frequency of operation. The interconnect function can be performed by an optically controlled switch. Such dipoles or patches, however, are inherently narrow in bandwidth. A departure in operating frequency by more than a few percent requires altering the switch states. Wide instantaneous bandwidth operation is unachievable, and such antenna elements provide interference to other nearby antenna elements in the array.
Thus, there is a need in the art for an antenna that can be used in a phased array without interfering with other nearby antennas in the array, while at the same time being extremely broadband. There is also a need for means to switch a photo-conductive antennas between its conductive and non-conductive states that is small and permits the assembly of an antenna array.
SUMMARY OF THE INVENTION
The foregoing needs of the prior art are satisfied by the present invention. A small, extremely broadband array of antenna elements is disclosed wherein individual antenna elements do not substantially interfere with other antenna elements in the array. A small optical switch is also disclosed which is used to selectively illuminate photo-conductive antenna elements to switch them between their conductive and non-conductive states.
The antenna elements are fabricated from a photo-conductive semiconductor material, such as silicon, that becomes conductive when illuminated by a light source and thus can serve as a metal-like electromagnetic antenna. A novel, small, light waveguide is taught which is used to mount the photo-conductive antenna elements and is also used to selectively illuminate and switch the antenna elements between their conductive and non-conductive states. The photo-conductive antenna elements mounted on the light waveguides form antenna array panels, and multiple panels can be stacked in a compact manner, and shared with a common exposure aperture. Each antenna array panel is designed to operate at a certain bandwidth section as a part of the total broad bandwidth of the system. The whole array of antenna elements offers a broad bandwidth capability, while retaining the advantages of a narrow bandwidth performance.
In addition, the antenna element array panels can be stacked very compactly which reduces side lobes; permits sharing of the exposure area/radome, dramatically reduces the system space-extension requirement, and decreases the radar signature. In accordance with the teaching of the invention the stacked antenna element array panels are mounted parallel to the radome and a ground plane.
The photo-conductive, silicon antenna elements on each antenna array panel are illuminated using a light waveguide, or optical tank, selectively fed with continuous wave laser light which provides uniform and efficient illumination of the antenna elements mounted on the array panel. The light tank waveguide is a thin slab of glass or sapphire with dielectric coated edges providing a mirror action to laser light in the substrate, and on which the photo-conductive semiconductor antenna elements are mounted. Laser illumination is delivered to the glass or sapphire by optical fibers and, due to reflection from the RF compatible, dielectric coated edges, the laser beam injected inside the optical tank reflects therein with little loss until absorbed by the photo-conductive, silicon, antenna elements.
With the photo-conductive silicon antenna elements bonded to the surface of the light waveguide, the higher refractive index of silicon makes the total reflection therein break down, and thus allows the laser beam to leak through the surface of the waveguide into the silicon antenna elements. When this occurs the silicon antenna elements becomes conductive and functions as a metallic antenna to receive and radiate electromagnetic energy. When illumination is removed from a light waveguide, the antenna elements thereon become non-conductive, appear as insulators, are electrically transparent to electromagnetic energy being transmitted by the antennas of other array panels, and thus give no interference to nearby active antenna elements.
With each antenna array panel designed to operate over an octave bandwidth, and by stacking multiple antenna array panels with each panel designed to operate over a different octave bandwidth, an extremely wide bandwidth antenna array is achieved. By phasing the signals applied to the antenna elements, phased array operation is achieved and the main lobe of the antenna elements can be electronically steered.
REFERENCES:
patent: 4782346 (1988-11-01), Sharma
patent: 4814773 (1989-03-01), Wechsberg et al.
patent: 5222162 (1993-06-01), Yap et al.
patent: 5374935 (1994-12-01), Forrest
patent: 5761351 (1998-06-01), Johnson
patent: 5926148 (1999-07-01), Liu et al.
Adams Stephen B.
Cleaveland Bryan L.
Edward Brian J.
Lockheed Martin Corporation
Marsh & Fischmann & Breyfogle LLP
Mull Fred
Tarcza Thomas H.
LandOfFree
Photonically controlled, phased array antenna does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photonically controlled, phased array antenna, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photonically controlled, phased array antenna will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2513418