Patent Application
20120249357
1. Field of the Invention
The present invention relates to radar systems and methods, such as missile radar systems and methods.
2. Description of the Related Art
Radomes are structures designed to cover antennas and thereby to protect them from direct exposure to aerodynamic and environmental conditions, while being as transparent as possible to the antenna's electromagnetic (EM) radiation. However many types of radomes include various forms of discontinuities or blockages. These discontinuities are not necessarily due to material changes, but in many cases due to shape changes. For example, radomes on high-speed, airborne platforms are usually equipped with a metallic tip to protect the radome against rain, erosion, etc. However there is room for improvement in this field of endeavor.
The metallic tip is at the very end of a dielectric/lossy edge which is an extension of the radome body, which is also lossy since it is the same material as the radome body. Surfaces inside the radome (cylindrical portion) that are at a certain distance from the main wedge have some blockage of the outgoing RF energy, but the blockage is not significant. Going further forward on the radome, in the region where the wedge begins to form, that part of the wedge acts almost as a metallic entity, especially at higher frequencies. This is because of the lossy material, combined with the wedge (i.e., the shape change), causes a significant blockage of the RF energy transmitted by the main antenna. That RF energy blockage causes a hole in the radiation pattern for the antenna, which is a bad thing since certain areas that are supposed to be covered by the RF energy, are in reality not covered. This lossy wedge, compared to the rest of the radome body which is cylindrical, causes a significant RF blockage, for the incoming or out coming RF energy. This lossy wedge has been found to lead to EM discontinuities for the main antenna located in the back of the radome. An approach to ameliorating these discontinuities, described in detail below, is to add a lossless wedge just before the metallic tip and go backwards between the radome tip and the antenna. This lossless wedge could be transparent glass or non transparent glass. The use of a lossless transparent material also provides the opportunity to introduce optics capabilities in addition to the removal of the radiation pattern hole.
According to an aspect of an invention, a missile includes different radiatively-transmissive materials in its radome body and its radome tip.
According to a still further aspect of the invention, a radome has an optically-transmissive tip.
According to another aspect of the invention, a radome has a tip that is substantially optically transparent.
According to yet another aspect of the invention, a missile emits encoded laser signals through its radome.
According to still another aspect of the invention, a missile radar system includes: a main antenna; and a radome enclosing the main antenna. The radome includes a radome body and a radome wedge. The radome body has a wide end and a narrow end, with the main antenna at the wide end, and the radome wedge at the narrow end. The radome wedge and the radome body include different materials that are substantially transparent to radar signals emitted by the main antenna.
According to a further aspect of the invention, a method of missile target guidance includes the steps of: receiving a reflected signal from an intended target of a missile, wherein the reflected signal is received at a seeker of a missile, after passing through an optically-transparent radome wedge of the missile; examining the reflected signal for the presence of signals not including encoding associated with the missile; and if the reflected signal includes signals including encoding not associated with the missile, rejecting and not using for navigation purposes the signals including encoding not associated with the missile.
According to a still further aspect of the invention, a method of improving performance of an antenna includes the steps of: providing a radome with a lossless, optically transparent radome wedge and a lossy dielectric radome body; and placing the antenna within the radome.
According to another aspect of the invention, a missile optical system includes: a radome having an optically transmissive front radome wedge; a seeker that within the radome that sends and receives optical signals on an optical path that passes through the optically transmissive front radome wedge; and one or more lenses in the optical path, between the seeker and the optically transmissive front radome wedge.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
The annexed drawings, which are not necessarily to scale, show various aspects of the invention.
A missile includes a radar system that has a radome through which a main antenna sends and receives signals. The radome includes a radome body at a relatively wide area of the radome, and a radome tip at a relatively narrow end of the radome, with the tip including the apex (edge) of the radome (the forward-most part of the radome). The radome body and the radome tip include different transmissive materials, with for example the radome body primarily made of a lossy optically nontransparent material, and the radome tip primarily made of a lossless (permittivity with low imaginary part) glass material that may also be optically transparent. A laser may be used in conjunction with the radome to send and receive encoded signals. The laser may be located behind (aft of) the main antenna, and one or more optical fibers may extend into and/or along the radome to guide laser signals to the radome tip. The laser may be used to emit encoded signals so as to allow multiple radar systems operating in the same area at the same time to discriminate between different targets.
The radome wedge (edge) 22 is also at least partially transparent to radiation emitted by and/or received by the antenna 14. Thus the radome wedge (edge) 22 may also be described as radiatively transmissive or optically transparent. However the radome wedge (edge) 22 includes a different material than the radome body 20. This may be an optically transparent material, such as a suitable glass, to make the radome wedge (edge) 22 optically transparent. The optical transparency may be to allow light to pass through the radome wedge (edge) 22, for example laser light, such as laser encoded signals, as described further below. It will also be appreciated that the radome wedge (edge) 22 may have a different material in order to withstand the forces it receives at the very front of the missile 10, which may result in heating beyond that experienced by the radome body 20. The glass of the radome wedge (edge) 22 may be suitable for the heat build-up and other environmental characteristics that will be encountered at the very front of the missile 12.
A metal tip 24 may be located at the front of the radome wedge 22. The metal tip 24 may serve to protect the radome 16 against rain or erosion, for instance.
More detailed explanations are now provided regarding the materials of the radome body 20 and the radome wedge 22. The radome body 20 is made of a lossy optically nontransparent dielectric material. Certain ceramics are examples of suitable lossy optically nontransparent dielectric materials. The radome wedge 22, in contrast, is made of a lossless dielectric, which includes very low lossy dielectric material, where the imaginary part of the dielectric constant is very low. The material of the radome wedge 22 may also be optically transparent. Certain glasses are examples of suitable materials for the radome wedge 22.
As used herein a “lossless material” or “lossless dielectric material” is a material for which
where σ is the electrical conductivity of medium (material), ∈ is the permittivity of medium, and ω is radian frequency, which is 2πf, where f is the frequency. A “lossy material” of “lossy dielectric material” is a material for which
A “conductive material” is a material for which
For purposes of these definitions a representative frequency f of 3 GHz may be used. Radomes such as those described herein may be used for frequencies in the range of 3-200 GHz, although these values should not be taken as limiting.
The radome body 20 and the radome wedge (edge) 22 may be coupled together by any of a variety of suitable means or methods. To give one example, the radome wedge (edge) 22 may be adhesively coupled to the radome body 20 using a suitable adhesive. Brazing is another method/means by which the radome body 20 and the radome wedge (edge) 22 may be coupled together. As another alternative, the radome body 20 and the radome wedge (edge) 22 may be parts of a single unitary continuous piece, for example formed in a single piece by diffusion of the materials of the radome body 20 and the radome wedge 22, such as occurs under elevated temperature. There may be a region along the border between the radome body 20 and the radome wedge (edge) 22 in which materials used in both the body 20 and the wedge (edge) 22 are present. There may be a material gradient near (in a vicinity of) a boundary 30 between the body 20 and wedge (edge) 22, with a gradual material change in a boundary region 32 from that of the radome body 20 to that of the radome wedge (edge) 22.
A laser 40 is located aft of the main antenna 14. The laser 40 is used to send encoded signals to illuminate a target of the missile 10. The signals are sent from the laser 40 along one or more optical fibers 42 that extend from the laser 40 to the radome wedge (edge) 22. The optical fiber(s) 42 may extend along the inner surface of the radome 16, and may be located at least partially within the material of the radome 16. The optical fibers 42 may be grouped in optical fiber bundles. The laser 40 and the optical fiber(s) 42 together may be considered to function as a laser designator 44, an optical emitter that illuminates the intended target with an encoded laser signal. For example the encoding may be contained in an encoded pulse train. The length of pulses, the pauses between pulses, and/or the intensity of pulses, may constitute an identifier or code substantially unique to the missile 10, and different from encoding utilized by other munitions. The reflected laser light (“sparkle”) from the intended target may be detected by a semi-active laser (SAL) seeker 46 that is located inside the radome wedge (edge) 22. The SAL seeker 46 may be or may include a bundle of optical fibers. Some of the optical fibers 42 may be used for transmitting signals from the seeker 46 to other components of the missile 10, such as a quad detector 48 or other suitable components aft of the main antenna 14, located in a fuselage 49 of the missile 10. The quad detector 48 may be used for detecting encoded pulse or other identifiers in incoming light signals, as described further below.
By detecting the encoding in the reflection of the encoded laser signals the fact that the missile 10 is targeting the illuminated target may be determinable by other missiles/munitions. Receipt by the seeker 46 of encoded signals having different encoding than the signals sent by the missile 10 indicates that another missile or other munition may be targeting the same target. This information may be useful in avoiding having multiple missiles/munitions targeting the same target.
The filter 52 and the SAL lens 54 may be mechanically coupled to the radome 16 using a nonmetallic structure 56. The nonmetallic structure 56 may be made of a suitable nonmetallic material, such as a suitable ceramic. Using a nonmetallic material for the structure 56 avoids interference in radar signals that would occur if a metallic structure was used.
The seeker 46 (
The encoding thus allows the missile 10 and 60 to distinguish between signals, and reject for navigation purposes all signals other than signals with the same encoding as the sent signal. Extraneous signals that are rejected may include encoded signals from other missiles (as in the illustrated embodiment), non-encoded signals from other munitions or targeting systems, or even spurious signals deliberately sent in an attempt to confuse targeting systems. The missiles 10 and 60 are able to focus only on the reflections of their own signals, which are the reflections of interest for targeting purposes.
In addition, the coding may be used to aid the missile in selecting a target, based on reaction of the coding scheme signal with the target. Different target surfaces will produce different interactions with the coded signals in producing a reflected signal. For example a burning vehicle will be expected to affect the signal (and its coding) differently than would a painted surface of an unburned vehicle. The missile 10 may be configured to detect and distinguish different types of reflections of the coded signal 10. This information may be used in prioritizing and/or selecting targets.
The use of coded signals as described above is not limited to missiles. It may be possible for the missile 10 to target other sorts of laser-guided munitions, such as laser-guided bombs, that are aimed at the same target that the missile 10 is targeting.
In addition to the advantages for allowing sending and receiving of optical signals, the radome 20 described above provides advantages in receiving radar signals, by avoiding radar signal degradation that occurred in prior art systems.
Unfortunately the signal strength does not have the ideal shape indicated in
From the foregoing it will be appreciated that many aspects of the present invention provide significant advantages over prior systems. Avoiding a lossy wedge (edge) prevents degradation of the signal strength of signals received by the missile's main antenna. Not only is a general degradation of signal strength prevented, but the problems of peak offset and low strength regions (RF holes) are avoided. In addition the angle of arrival is also corrected. The use of a substantially optically transparent radome tip allows employment of optical imaging through the radome. The employment of a seeker allows for designation of a specific target that the RF-guided missile should strike. The use of a seeker, in conjunction with a laser for illuminating the target, increases the precision of guidance toward a desired target. It also enables flexibility in targeting, and fast-reaction targeting. Finally, the use of encoded laser signals allows detection by the missile of situations where multiple munitions are aimed at the same target. Furthermore the use of encoded optical signals allows the missile to select and prioritize targets dynamically or based on priory information for certain targets.
Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
