Abstract:
A reflected energy detecting device includes a transmitter for transmitting an electromagnetic signal and a receiver for receiving a reflected electromagnetic signal. An antenna may be operatively connected with the transmitter and the receiver for radiating the electromagnetic signal and capturing the reflected electromagnetic signal and the antenna may be movable. A main controller may be provided for controlling operation of the transmitter and the receiver and the movement of the antenna and the reflected energy detecting device may further include at least one platform. The at least one platform may support a remote reflector that is dimensioned and configured to redirect the transmitted electromagnetic signal in a desired direction and a platform controller that is configured to communicate with the main controller and to maintain alignment between the remote reflector and the antenna.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to devices and methods for detecting reflected energy and, more particularly, to radar and ladar systems with enhanced range. 
   2. Related Art 
   The effective range of ground based radar and ladar systems for detecting, tracking and/or destroying targets, such as low flying aircraft and cruise missiles, is limited by line of sight. The line of sight in various directions from any particular location may be defined by the curvature of the earth and/or terrain features such as valleys, mountains and hills. This poses serious concern where it is necessary to detect and engage multiple targets in order to prevent a loss of life at a range that is greater than the effective range of the radar or ladar system. 
   In an attempt to increase the effective range, radar and ladar systems have been remotely located on towers, in aerostats, airships and aircraft. This requires that hundreds of pounds of electrical equipment requiring tens of kilowatts of power must be located remote from the ground. Military personnel must operate and maintain this radar hardware while it is remote from the ground. Accordingly, hardware weight, size, power requirements, operability, and maintainability make remotely locating these systems difficult and extremely expensive. Therefore, to date, no suitable device or method of increasing the effective range of radar or ladar is available. 
   SUMMARY OF THE INVENTION 
   In accordance with an embodiment of the present invention, a reflected energy detecting device comprises a transmitter for transmitting an electromagnetic signal and a receiver for receiving a reflected electromagnetic signal. An antenna may be operatively connected with the transmitter and the receiver for radiating the electromagnetic signal and capturing the reflected electromagnetic signal and the antenna may be movable. A main controller may be provided for controlling operation of the transmitter and the receiver and the movement of the antenna and the reflected energy detecting device may further comprise at least one platform. The at least one platform may support a remote reflector that is dimensioned and configured to redirect the transmitted electromagnetic signal in a desired direction and a platform controller that is configured to communicate with the main controller and to maintain alignment between the remote reflector and the antenna. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will be evident to one of ordinary skill in the art from the following detailed description made with reference to the accompanying drawings, in which: 
       FIG. 1  is a diagrammatical view showing a reflected energy detecting device, in accordance with an embodiment of the present invention, that is employed to detect a target, such as a cruise missile, traveling over a mountainous terrain; and 
       FIG. 2  is a diagrammatical view showing the reflected energy detecting device of  FIG. 1  embodied in multiple platforms. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   One embodiment of the present invention concerns locating a reflected energy detecting device such as radar or ladar hardware at ground level and transmitting a radar/ladar beam upward to an elevated platform that comprises a reflector and, optionally, a refractor or phase shifter. Ground control of the elevated reflector and the phase shifter may be made by radar/ladar operators through telemetry links. Translational and rotational position control, along with vertical referencing and stabilization, of the reflector and phase shifter may enable ground based radar operators to view over the horizon with a minimum amount of elevated hardware. Requirements for elevated radar operations are thus greatly reduced over those required in the prior art as ground based radar personnel are able to operate and maintain the radar/ladar hardware. The pointing and positional control for the reflector and the phase shifter may be the only functions that require hardware operation while located in the elevated position. Multiple reflectors and phase shifters may be employed for covering even very mountainous terrain. 
   It will be appreciated that radar beams transmitted from high gain radar antennas do not spread rapidly for an appreciable distance after leaving their antennas. This enables the reflection and phase shifting of these beams by reasonably sized electrical reflectors and phase shifters. Also, the reflectors may be very light weight because, it is believed, that the electrical reflection phenomena takes place very near the surface of a reflector. 
   The phase shifter may comprise an array of computer controlled phase shifters such as a space fed, phased array radar antenna. It will be understood that the phase shifters can be optionally embedded into a reflector such that steering of the beam can be accomplished at the reflector. Simple telemetry links may enable ground based control of these elevated reflectors and the associated phased array antennas elements. Sensors and simple low powered actuators can be located at the elevated reflectors to provide reflector positioning stabilization and pointing. The elevated reflector may feed the phased array antenna by reflecting the radar beams directly into this array. Beam steering or pointing of the elevated phased array can be controlled by electrically controlled phase shifters as is commonly provided space fed phased array radar antennas. 
   The elevated reflectors and phase shifters may be supported by platforms such as towers which may be mobile, tethered vehicles including aerostats or aerodynamic vehicles, or aircraft that may be manned or unmanned. The reflectors and phase shifters supported by towers and tethered vehicles may receive power and communications via, e.g., wired and/or wireless links. The reflectors and phase shifters supported by aircraft may be controlled by, e.g., microwave links and, it will be appreciated that the electrical energy requirements for reflector and/or phase shifter stabilization, positioning and/or pointing are minimal and well within the capability of existing aircraft power systems. 
   Referring now to  FIG. 1 , a reflected energy detecting device, in accordance with one embodiment of the present invention, is illustrated generally at  10 . The reflected energy device is illustrated as being employed on a surface  12  of a terrain including mountains  14 . A target  16 , such as a terrain following cruise missile, is shown approaching the reflected energy detecting device  10 . 
   In the illustrated embodiment, the reflected energy detecting device  10  may comprise a ground transmitter/receiver  18 , a main or ground controller  20  and a platform  22 . The ground transmitter/receiver  18  is preferably operated at a radar frequency, although, other frequencies including light frequencies may be employed. The ground transmitter/receiver  18  comprises an antenna  24  from which a transmitted electromagnetic signal may radiate as illustrated by arrows  26 . As shown, the electromagnetic signal may be reflected from the target  16  as a reflected electromagnetic signal represented by arrows  28 . Together the electromagnetic signal and reflected electromagnetic signal may form a beam  30 . The antenna  24  is preferably of a directional type and may also be focused, in a known manner, at infinity or at a particular distance other than infinity. Also, it will be recognized that a more efficient reflected energy system may be possible by focusing the electromagnetic energy, in a known manner, as it is transmitted from the ground location. For example, very high intensity radar beams may be focused at a remote reflector to increase the efficiency of the transferred energy which may then pass these high intensity beams to space fed, phased array antennas for delivery of more power to the target than would be available from an antenna based system focused to infinity. 
   The ground transmitter/receiver  18  may be mounted to a trailer  32  for ease in mobility and may include an omni-directional antenna  34  for communicating with the ground controller  20 . 
   The ground controller  20  may be located within a truck  36  and may comprise a transmitter/receiver (not shown) for telemetry, antennas  38  and a computer system (also not shown) running tailored software for operation of the reflected energy detecting device  10 . The ground controller  20  functions to control operation of the ground transmitter/receiver  18  in a known manner while also communicating with a platform controller (described in more detail below) which is located on the platform  22 . It will be understood that while the ground controller  20  is described as communicating with the ground transmitter/receiver  18  via wireless, this is for illustrational purposes and a wired system may be employed in the practice of this invention. 
   The platform  22  may comprise, e.g., a tower, an aerostat, an aerodynamic vehicle, or an aircraft (manned or unmanned) which may support a reflector assembly  40  and a platform controller system  42 . The reflector assembly  40  may comprise a reflector  41  that may be composed of radar and laser surface reflecting materials such as aluminum, silver or other electrically conducting materials. The reflector  41  may also comprise a metallic foil disposed on a polymeric substrate or a metallic screen for light weight. The reflector  41  may be connected to the platform  22  by a reflector interface  44  which in conjunction with a stabilization and vibration isolation control  46  and a rotational and translational control  48 , of the platform controller system  42 , effects reflector position and stabilization. This provides both for movement of the reflector  41  for directing the beam  30  in a desired direction and for mechanical isolation of the reflector from translational and rotational movements of the platform  22  that can occur as the result of air turbulence, winds or repositioning of elevated hardware. Also, the reflector  41  may be stably positioned above the ground transmitter/receiver  18  so that an antenna attitude control of the ground controller  20  can align the antenna  24  so that its beam  30  may be transmitted to the reflector  41  and on to the target  16  whereby returns from the target are scattered back along this same path. To achieve this result, it will be appreciated that position and attitude sensors may be employed in a known manner on the reflector  41  and platform  22  for precise stabilization and positioning of the reflector. 
   Alignment of the antenna  24  to the reflector  41  may be necessary prior to operation. Maintenance of this alignment may be provided automatically by a positional control system, e.g., co-located in the platform controller  42  and ground controller  20  after initial alignments are made. 
   The telemetry interface provided by the transmitter/receiver of the ground controller  20  and a platform reflector control computer  50  of the platform controller  42  greatly simplifies initial alignments of the antenna  24  and reflector  41  and maintenance of these alignments. It will be appreciated that the telemetry interface may be through wired system such as fiber optics, or via a wireless microwave link depending on the application and the platform employed. 
   After initial alignment operations, an operator may operate the reflected energy detection device  10  in a known target search, track, or search while track mode. 
   The reflector  41  may be rotated via rotational and translational control  48  whereby targets may be viewed throughout 360 degrees of azimuth. Instructions for control of the reflector  41  may be made through the ground controller  20 , the transmit/receive telemetry to/from the platform controller  42  and the rotational/translation control  48 . 
   Optionally, a phase shifter array  52  may be employed to increase the operational capability of the reflected energy detector  10 . The phase shifter array  52  preferably comprises a space fed, phased array radar antenna. The phase shifter array  52  may function in a known manner such that the beam  30  may be phase shifted or steered to a desired location. Also, the phase shifter array may, in a known manner, may be employed in the detection and tracking of multiple targets. A phase shifter array controller  54  may be provided which communicates with the ground controller  20  whereby operational control of the phase shifter array  52  may be effected. It will be appreciated that the reflector  41  and phase shifter array  52  may be integrally connected as a one-piece system. 
   Referring now to  FIG. 2 , a multiple platform reflected energy detecting device is illustrated generally at  100 . The reflected energy detecting device  100  may be similar to the reflected energy detecting device  10 , described above, and thus similar reference numbers are used to refer to similar components. As illustrated, the reflected energy detecting device  100  may be employed on a surface  112  of a terrain including mountains  114  and a target  116  may approach the device  100 . 
   The reflected energy detecting device  100  may also comprise a ground transmitter/receiver  118 , a main or ground controller  120  and, as shown, multiple platforms  122 . The ground transmitter/receiver  118  is also preferably operated at a radar frequency and comprises an antenna  124  from which a transmitted electromagnetic signal or beam  130  may radiate as illustrated by arrows  26 . As shown, the beam  130  may be reflected from the target  116 . The ground controller  120  functions similar to the ground controller  20 , except in a multiple format, to control and align reflectors and/or phase shifter arrays of each platform  122 . 
   The present invention enables, e.g., the location of high power reflected energy detecting capability at elevations that may look over the earth&#39;s curvature and interfering terrain features. Location of reflector fed phased array antennas as high as 20 Kilometers with ranges of 400 kilometers to the earth&#39;s horizon appears possible. There are applications where this concept could provide airborne reflected energy surveillance at a fraction of today&#39;s cost. Advantages of the present invention over present methods of elevating a reflected energy system include reductions in the weight and power requirements of the elevated hardware, simplified operation and maintenance of the hardware and simplified platform configuration as structures to support the reflector hardware need only a fraction of the strength of that necessary to support an entire reflected energy system. For example, aerostats and aircraft can support and operate reflector/refractors at a fraction of the cost and effort of elevating a complete reflected energy system. 
   While the present invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the present invention is not limited to these herein disclosed embodiments. Rather, the present invention is intended to cover all of the various modifications and equivalent arrangements included Within the spirit and scope of the appended claims.