OMNIDIRECTIONAL BACK REFLECTION PASSIVE DECOY Technical Field of the Invention

This invention is related to an array of reflectors (Figure 1 ) produced by adjoining 8 units of trihedral corner reflectors with specific angles to attain bicentric, strong and consistent back reflections of radar waves to be utilized for breaking lock of the radar homing missiles.

Prior Art

Decoys are countermeasures utilized for distracting enemies' attention from the zone of the target towards a different zone. Decoys generally mimic certain objects and strive for appearing in enemies' smart systems. The enemy moves towards the decoy in case the object used for a decoy manages momentarily to distract enemies' attention from the real target; and thus the decoy is deemed to have fulfilled its objective. "Decoy" in English refers to the model of a bird, animal, or an object that is used for shooting or entrapping the others. Words meaning "bait", "decoy" (false duck used for hunting ducks), "decoy", or "deceiver" is used in Turkish language for such cases. -

Decoys may be in a couple of types:

- Passive decoys that solely reflect the received signal,

- Methods of preprogrammed jamming of the signal back reflected from receiver frequency or signal masking, that are termed as active deception,

- Lastly, active decoys that attain receiver-transmitter performance by means of processing collected data via computer.

Passive decoys might only be effective if they are designed in an outstanding manner, and might be visible to the counterpart only if they have very big dimensions. Passive decoys physically scatter the radar signals that they receive. No processes such as amplification is applied to the signal. Passive decoys are identical with passive reflectors. Though the passive reflectors are small, they have a critically important usage area, and are the indispensable elements of especially the sailing vessels. Small or medium sized vessels are very small targets in terms of radar reflectivity, and they frequently become overshadowed by larger targets. Hence, these vessels will not be visible to search radars in cases of emergencies such as being lost or kidnapped if the visibility conditions are not favorable. Therefore, the vessels hang these small reflectors to a higher location on their vessels, in order for enhancing their visibilities on radar screens under such adverse conditions. Reflectors are mounted to the highest point available on the vessel's post in smaller marine boats, for minimizing loss of range resulting from earth's surface curvature. Conical or cylindrical cased reflectors are preferred so that they would sustain the strong loads of winds over the post. Thanks to their proper design patterns, these small sheet reflectors reflecting the received signal have a radar cross section larger than the vessel itself.

Another area of use for the passive decoys is utilization of these as floatingpassive targets by means of inflating over the water, and thus protecting ships from smart missile systems. Decoys that imitate the appearance of ships in radars reflect the radar signals back to their sources. Physical decoys should be produced with utmost accuracy so that they would be visible to the oncoming missile.

Main principle of active decoys is as follows; the defense radar should be aware that it should construct a decoy system. This system creates certain signals, and emits these signals along with the signals radiated from the target. The radar in question thus should become incapable of differentiating whether the signal received comes from the decoy or the real target.

Active decoys are some kind of signal jammers. The aim of these jammers is not transmitting noise to the radar but transmitting false and defective signals similar to the signals that the radar anticipates. Hence, the radar is deceived with false information by this means. Electronic jamming is the process of deliberately transmitting electromagnetic (EM) energy in order for preventing effective usage of electronical devices, hardware and systems by the enemies, or transmitting a signal created similar to the received signal, or reflecting the EM energy received.

Whereas the process of deliberate transmission, re-transmission, reflection, absorption, concealment or modification of electromagnetic energy in order for transmitting deceptive information either to electronical correspondence systems/devices of the enemy that operate through EM spectrum, or to the enemy itself, with the objective of weakening or disabling the enemy's electronic warfare power is termed as "electronical deception".

Passive decoys operate on identical principles with passive radar reflectors. Passive decoys physically reflect the radar waves they receive. Their difference is that having been designed and produced in smaller sizes than the target they are to replace, while supplying reflectivity on target's radar cross-section or on a cross-section highly close to that in question.

The purpose for utilizing passive decoys for military purposes is allowing escape of fighter aircrafts, helicopters and vessels from radar homing missiles by using decoys at the moment of attack in order for preventing them from the radar guided missiles.

Reflectors are devices that produce generally strong back reflections along the direction of the source; and the power of this reflection might be dependent on the direction of the reflector.

Electromagnetic, acoustic and other wave reflectors have been known since the Fessenden patent (1 .384.014) of 1921 . These devices reflect the wave energy preferably towards the direction of the source. This results in a stronger back reflection of energy in cases where reflections in all directions are of the same power.

In order for radar waves to backscatter, the wave should possess both an amplitude and a phase, just as it is the case for light and sonar waves. For the two waves to interact with each other in a way to mutually enhance each other, their phases should be majorly equivalent. In cases where they have quasi-opposite phases, they would be interacting in a mutually absorptive manner. To attain a strong back reflection from the reflector, inner surfaces of two corners should be visible from a specific incident angle, and the back reflected waves should be interacting in a mutually enhancing manner. The sufficient condition to determine is having the length of the reflection path from respective two corners not larger than one quarter of the wavelength of the incident field.

Certain decoys designed for this purpose are of buoyant types, and they encompass radar reflectors with the same radar cross sections as the vessel they would be replacing. These decoys are allowed to float within a specific reaction time as an attack realized by radar guided missile is detected by the vessel. Hence, the vessel escapes by maneuvering behind the decoy, as the radar homing missile moves along by locking on the decoy. Thus, the decoy is hit by the guided missile instead of the vessel.

The first patent regarding the passive decoys as per the current state of the technique is the patent no US 3.938.151 , developed by Treman in 1976. The protected object in this patent was a cylindrical shaped plastic balloon that had antenna circuits in Van Atta array on its surface.

Another patent for the current state of the technique (GB212148A) mentions readily inflatable balloons that might be used for attracting radar-guided missiles. These balloons can be produced from fine rubber or latex, they take up little space when folded with care, and can be enfolded within the idle anti-missiles. These packages also contain a cylinder that would provide the high pressure for the balloon to inflate. Outer surface of the latex can be coated with an extra-fine metallic spray for obtaining a subtile radar appearance.

Patent numbered GB2189079 A, which is another patent for the current state of the technique, contains flexible radar reflecting panels attached to an inflatable frame. Three interpenetrating balloon structures of the same size filled with air is mentioned for the structure of frame. In this reference, radar-reflecting panels were constructed such that they created 8 units of radar reflecting surfaces. These reflectors were square-shaped and were attached to the inflatable frame from their corners. Another related patent numbered US2004/0227657 A1 found for the current state of the technique describes the design related to a buoyant decoy developed again for military radar homing missile threats. The decoy mentioned in this patent was being carried along a rocket launched from a launching pad. In this system, the rocket launched from the launching pad could carry along multiple decoys. Each of the decoys being launched this way contain corner-reflecting structures and were dropped in a predetermined location along the flight path. The reflector used for the decoy is again in corner reflector form, and consists of 8 units. Mostly the launching and control systems are described in this patent and are taken under protection. Characteristics of the material of which its reflectivity was utilized is not mentioned. The decoy in the patent numbered US 2007/0046524 is launched with a launching system as described for the previous patent. In this patent, the radar reflector utilized for misleading the missile glides down by transforming into a parachute after being thrown off the rocket. This decoy is designed to contain at least four units of trihedral corner reflectors. It is mentioned that the radar reflectors of this patent could be produced from Nylon fabric metallized with virgin silver or from any other fine fabric suitable for production of reflectors.

Along the patent numbered US 2004/6742903 reviewed for the current state of the technique, it was mentioned that a single-centered quasi-omni-directional, strong and consistent radar wave was attained particularly on horizontal axis (azimuth) with the integration of 6 units of trihedral corner reflectors in specific angles. Technical Problem that the Invention Aims to Solve

Decoys might consist of an array of corner reflectors; each of them directed differently. Corner reflectors were primarily used for reflecting radar waves in the beginning, and it is just recently that they have became important for lights too as for lasers. While most of the waves provide a strong back reflection towards the source in incident direction, some of them commonly provide a weak reflection in a wide range. This might be a critical restriction. For instance, small boats utilize radar reflectors for being detected by radars of larger vessels under foggy conditions. This method assists in prevention of collisions. However, in cases where directions with weak reflections exist, the vessels approaching from these directions might not be detected by radars of other vessels, and a collision might occur. Having back reflections of equal power is thus considered as critical. When the radar waves are sent exactly towards the corner of the reflector, a highly strong reflection in each incident direction is formed for all three surfaces making up the reflector.

Corner reflectors termed as trihedral are structures that provide three reflections, each one of them being generated by one of the inner surfaces (Figure 2). It is convenient to use trihedral reflectors for attaining a strong radar reflection. Trihedral reflectors would be reflecting radar waves coming parallel to one of its surfaces at least twice on its remaining surfaces. Back reflection of radar waves would thus be more strong because of the two coherent reflections. A novel instruction for corner reflectors was described in the patent numbered US 2004/6742903. This was an instruction that provided visibility of the interior of a corner while also making the interior of a second corner visible. Phase coherence provides an enhancing interaction between reflections radiated from the first and second corner reflectors. Coherence in this patent was attained with an arrangement that makes interior corners of corner reflectors draw closer together. This arrangement results principally in a smooth and strong back reflection.

There are blind angle zones for which radar cross sections cannot be obtained in reflector arrays that consist of 8 units of equilateral trihedral reflectors in rain-catch position, and 8 units of corner reflectors. As an alternative to these, a quasi- omnidirectional radar cross section values was solely obtained in horizontal direction for the sequential reflector, whose geometry was presented and defined in the patent numbered US 2004/6742903.

The "omnidirectional Back Reflection Passive False Target" and its sequential reflector array that is the subject of this specification were adjoined in the most convenient angle to provide coherent, strong and consistent radar wave back reflections. By this means, periodical radar cross section (amount of reflection -) inflicted on this reflector was increased compared to the reflectors existing as per the current state of the technique, and thus the average radar cross section value was raised. Nevertheless, different from the reflectors alike, no blind zones with respect to radar cross section at any angle were created with this reflector having an array of this structure; even for incident angles within the range of +/- 10° on vertical angle (elevation) rotated 360° on horizontal axis, and for different radar frequencies.

Description of the Drawings

Figure 1 : Perspective view of the omnidirectional back reflection passive decoy

Figure 2: Standard trihedral corner reflector Figure 3: Frontal view of the omnidirectional back reflection passive decoy

Figure 4: Side view of the omnidirectional back reflection passive decoy

Figure 5: Junction of trihedral reflectors in a group with 4 elements

Figure 6: Reflector array created by adjoining 2 sets of trihedral reflectors in a group with 4 elements Figure 7: Top view of the omnidirectional back reflection passive decoy

Figure 8: Radar Cross Section graph of omnidirectional back reflection passive decoy for different radar frequencies with respect to horizontal angle

Figure 9: Radar Cross Section graph of omnidirectional back reflection passive decoy at the frequency of 9 GHz for different incident vertical angles with respect to horizontal angle

Elements of the graphs are numbered, and their respective descriptions are as follows: 101 : Reflective surface 102: Central corner of reflectors 103: Central corner of reflectors 201 : Reflective surface 202: Central corner of reflectors Description of the Invention

Objective of this invention is designing an array of reflectors (Figure 1 ) by adjoining 8 units of trihedral corner reflectors with certain angles to attain bicentric, strong and consistent back reflections of radar waves to be utilized for providing an efficient deception regarding the radars of radar homing missiles and breaking the lock of these radar guided missiles.

This invention is an array of reflectors created by adjoining corner reflectors one by one from their center points and consequent rotation of these with a specific angle. This structure was opted for increasing the periodical minimum radar cross section over the range of desired angles and for attaining a strong back reflection. There are 8 corner reflectors and each corner reflector provides strong back reflections also over 60° in horizontal angle with respect to radar cross section. By this means, whenever the reflector provided in Figure 1 is rotated with a 360° angle, one corner reflector as a whole would be detected by radar systems at any angle (Figure 8).

Radar cross section analyses of omnidirectional back reflection passive decoys performed with numerical simulation methods with respect to horizontal angle for different radar frequencies is depicted in Figure 8. According to this graph, a passive radar reflector that does not create blind angle zone with respect to radar cross section at different horizontal angles, and that supplies omnidirectional radar cross section values at horizontal angles for different radar frequencies was designed. With this invention, periodical minimum radar cross section value attained from the radar reflector was increased and thus an increase on the average value was achieved (Figure 8).

Radar cross section analysis results of omnidirectional back reflection passive decoy for different incident angles at +/- 10° vertical angles with respect to horizontal angle performed by numerical simulation methods at the frequency of 9 GHz, which is critical for radars, as depicted in Figure 9. Accordingly, no blind zones with respect to radar cross section are created with this reflector having an array of this structure for any angle; even for incident angles within the range of +/- 10° vertical angle (elevation) rotated 360° on horizontal axis. Radar cross section value does not almost decrease at different radar frequencies within the horizontal angle range in this invention, up to +/- 10 degrees of incident vertical angles (Figure 8, Figure 9).

4 units of trihedrals are adjoined in a way that their centers come together (Figure 5). The top corners of these reflectors are located such that the edges in their centers would not be detached from each other, and to create a 45 degrees angle with respect to elevation on z-axis (Figure 5). Due to the direction of this angle, outer each triangular reflector create another reflector as if the reflectors' outer edges are interpenetrated (Figure 5).

A 180 degrees rotated counterpart of this structure is located on this reflector in the same axis direction at a distance of 80 wavelengths (Figure 6).

Passive decoys, in this pattern of adjoining, generate an interior-faced square-based pyramid on both top and bottom sections (Figure 7).

Two center points exist in the structure (Figure 1 ). These center points are located on the same axis, with a distance of 80 wavelengths between them. Square pyramids are generated by themselves and the crown of each square pyramid constitute a center point (Figure 7). Radar cross section averages of omnidirectional passive decoy is higher compared to all trihedral reflectors and reflector arrays. Value of radar cross section almost does not decrease and does not create blind zones with respect to radar cross sections, and in addition to these; this geometrical structure demonstrates a steady distribution at all angles.

Reflectivity in this invention is attained with the utilization of metal sheets or metal fibers, metal wires; or with fabrics produced with metal coatings.

Radar reflector used in this invention is joined by either welding or stitching the reflective surface to the bearer, for attaining proper tightness that would provide the maximum value; i.e. for creating a smooth-form surface such that it would provide the anticipated radar cross section.

This structure might be located on a buoyant platform, since it would be used as a deceptive system for battleships. This structure might as well be used by mounting on vessels, boats, etc., along with an inflatable carcass produced from a material that could be inflated with air or other kinds of gas. 8 units of equilateral trihedral reflectors, with side lengths of 158 wavelengths or any other length determined according to the required radar cross section were utilized for this invention (Figure 1 ). Whereas the preferred side or perpendicular side length was determined according to passive decoy's capability of providing a higher omnidirectional radar cross section than that of larger battleships. The structure shall be produced with materials with high electromagnetic reflectivity such as aluminum, steel, etc. or with fabrics produced from metal sheets or by using metal fibers or wires, or that are metal-coated.

The structure might be used by mounting on another buoyant structure so that it would float on water or by mounting the reflective array in question on an inflatable structure, since the structure would be used as a deceptive system for battleships. With its capability of providing a quasi-omnidirectional radar cross section value at +/-10 degrees on the vertical angle, the structure also might effectively be used on sea waves that make it bend at +/-10 degrees above the water.

The reflector array that is the subject to this invention is produced by cutting pieces from metal sheets and joining them by hinges or by welding to produce the form given in Figure 1 . This array might also be produced by cutting pieces from textile surfaces such as metal coated or that contain metal fibers or metal wires (from woven or knit fabrics or nonwoven textile surfaces), and joining them together by stitching or by other methods to produce the form given in Figure 1 .

Development of numerous applications regarding the "omnidirectional back reflection passive decoy" is possible within the scope of these basic principles, and the invention shall not be restricted with the examples described herein.

Industrial Applicability of the Invention

This invention is created with the preparation of equilateral triangles with one side length of 158 wavelengths or any other length to be determined by calculating according to the required radar cross section value, in order for producing a reflector. Required pieces for the production of the design given in Figure 1 is produced by cutting, and these pieces are then joined to form the structure in question.

Metal sheets or metal coated or metal containing textile surfaces (from woven or knit fabrics or nonwoven textile surfaces) are used for triangles for attaining reflectivity. These pieces are then joined by welding or stitching according to the very nature of the material utilized.

This structure might be located on a floatingplatform, since it would be used as a deceptive system for battleships. This structure might as well be used by mounting on vessels, boats, etc., along with mounting on an inflatable carcass.