Abstract:
The present invention is a man-portable counter-mortar radar (MCMR) radar system that detects and tracks enemy mortar projectiles in flight and calculates their point of origin (launch point) to enable and direct countermeasures against the mortar and its personnel. In addition, MCMR may also perform air defense surveillance by detecting and tracking aircraft, helicopters, and ground vehicles. MCMR is a man-portable radar system that can be disassembled for transport, then quickly assembled in the field, and provides 360-degree coverage against an enemy mortar attack. MCMR comprises an antenna for radiating the radar pulses and for receiving the reflected target echoes, a transmitter that produces the radar pulses to be radiated from the antenna, a receiver-processor for performing measurements (range, azimuth and elevation) on the target echoes, associating multiple echoes to create target tracks, classifying the tracks as mortar projectiles, and calculating the probable location of the mortar weapon, and a control and display computer that permits the operation of the radar and the display and interpretation of the processed radar data.

Description:
CROSS REFERENCE To RELATED APPLICATION  
       [0001]     The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/553,262, filed Mar. 15, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to radar systems and, more specifically, to a man-portable counter mortar radar (MCMR) system capable of 360 degrees of coverage over extended ranges.  
       DESCRIPTION OF PRIOR ART  
       [0003]     The mortar is a projectile weapon that launches explosive shells in high trajectories to penetrate enemy revetments and trenches and to inflict damage on enemy equipment and personnel. It is a light-weight, low-cost weapon, that can easily be carried and deployed by foot soldiers. The mortar can be operated effectively from dense cover, and can be moved quickly to different locations, to avoid counterattack.  
         [0004]     Countering a mortar attack is a difficult technical and tactical problem, due to the ubiquity and flexibility of the weapon. The current practice consists of deploying a large and very accurate radar (for example, the United States AN/TPQ-36) to detect the incoming projectiles, compute their trajectory, and determine the launch point location. Then, an immediate counterattack can occur, using mortars or artillery, before the enemy can move his weapon.  
         [0005]     Conventional counter-mortar radars are very large, vehicle mounted systems capable of 90 degrees of coverage. Such systems employ large, high-power, precision planar array antennas to determine accurate launch point locations at extended ranges. Present mortar-locating radars are also highly specialized to their single task, and have little capability for other useful radar functions; for example, defense against attack by airplanes or helicopters. The radar system cannot be moved quickly, thus rendering it vulnerable to mortar attack. The radar is also sufficiently costly, in equipment and operating personnel, that only a limited number can be assigned to any single battalion.  
       OBJECTS AND ADVANTAGES  
       [0006]     It is a principal object and advantage of the present invention to provide a portable counter mortar radar system that is carried or moved with ease.  
         [0007]     It is an additional object and advantage of the present invention to provide a portable counter mortar system capable of 360 degrees of azimuth coverage.  
         [0008]     It is a further object and advantage of the present invention to provide a portable counter mortar system capable of mortar location to 5 kilometers with a fifty percent CEP accuracy of 100 meters.  
         [0009]     Other objects and advantages of the present invention will in part be obvious, and in part appear hereinafter.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention comprises a man-portable counter mortar radar (MCMR) system including a cylindrical phased array antenna mounted on a tripod to provide 360 degrees of azimuth coverage. A receiver-signal processor (RSP) unit is interconnected to the phased array antenna and provides signal conversion, detection, tracking and weapon location. The MCMR system is operated locally by a notebook computer. Power for the MCMR system may be provided by vehicle auxiliary power, a small gasoline generator, or from battery depending upon the particular situation and duration of operation.  
         [0011]     It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate a preferred embodiment of the invention, and together with the description serve to explain the principles and operation of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention will be further understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:  
         [0013]      FIG. 1  is an exploded perspective view of a MCMR system according to the present invention.  
         [0014]      FIG. 2  is a perspective cutaway of an antenna array according to the present invention.  
         [0015]      FIG. 3  is a schematic of the circuitry for the electronically steered antenna array according to the present invention.  
         [0016]      FIGS. 4   a  and  4   b  are opposing side elevation views of an antenna column panel according to the present invention.  
         [0017]      FIG. 5  is a photograph of a transmit matrix switch assembly according to the present invention.  
         [0018]      FIG. 6  is a photograph of a receive matrix switch assembly according to the present invention.  
         [0019]      FIG. 7  is a schematic of antenna beam positions according to the present invention.  
         [0020]      FIG. 8  is a graph of azimuth beam patterns according to the present invention.  
         [0021]      FIG. 9  is a graph of elevation beam patterns according to the present invention.  
         [0022]      FIGS. 10-13  are elevation views of an MCMR at various stages of assembly.  
         [0023]      FIG. 14  is an elevation view of a tripod according to the present invention.  
         [0024]      FIG. 15  is a perspective view of an antenna connector ring for interconnecting the antenna cylinder to the tripod.  
         [0025]      FIG. 16  is a block diagram of the radar electronics that are housed in the antenna cylinder according to the present invention.  
         [0026]      FIG. 17  is a block diagram of a waveform generator according to the present invention.  
         [0027]      FIG. 18  is a block diagram of a receiver downconvertor according to the present invention.  
         [0028]      FIG. 19  is a block diagram of a digital signal processor according to the present invention.  
         [0029]      FIG. 20  is a block diagram of the hardware of an MCMR system according the present invention.  
         [0030]      FIG. 21  is a block diagram of the firmware of a digital signal processor according to the present invention.  
         [0031]      FIG. 22  is a block diagram of software for operating a MCMR according to the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0032]     Referring now to the drawings, wherein like numerals refer to like parts throughout, there is seen in  FIG. 1 a  MCMR system  10  according to the present invention. MCMR system  10  generally comprises an antenna  12 , a laptop computer  16 , and a power supply  18 .  
         [0033]     Referring to  FIG. 2 , antenna  12  comprises an L-band, 24-column cylindrical phased array radar mounted on a lightweight tripod  20 . Antenna  12  scans electronically in azimuth using an electronic matrix switch and has a pair of fixed elevation beams. Both azimuth and elevation monopulse angle measurement is used to provide accurate three-dimensional target coordinates (range, azimuth, and elevation).  
         [0034]     Antenna  12  is constructed of 24 radially extending antenna panel columns  22 , spaced at fifteen degrees and mounted by support rings  24  to a central antenna cylinder  26  that houses a transmit matrix assembly  28  and receive matrix switch assembly  30  of which there are two, as well as a receiver  42 , digital signal processor  44 , waveform gerneator  46 , and CPU  48 , as illustrated in  FIG. 16 . Antenna panel columns  22  can be removed and stacked for transport, and can be quickly reassembled when the radar is deployed.  
         [0035]     Referring to  FIGS. 3 and 4 , each panel column  22  is an etched substrate containing six vertically polarized dipole elements  22   a , each with a pre-selector filter, limiter, and low noise amplifier. The six elements are combined on panel column  22  to form two stacked elevation beams that are offset in elevation angle by 17 degrees. A single elevation beam is generated on transmit, centered on the lower receive elevation beam. The elevation beams are independently tapered in amplitude and phase to reduce the below the horizon elevation angle sidelobes to suppress the effects of ground-bounce multipath. Each panel column  22  also contains a pair of solid-state power amplifiers  22   b  that generate 30 Watts of peak RF power at up to a 10% duty cycle. Each power amplifier drives three elements through an unequal split, three-way power divider. Panel column  22  further comprises cable connectors  22   c  for electrical interconnection to radar electronics housed in central antenna cylinder  26  and longitudinal slots  22   d  formed parallel and adjacent to their respective inner edges. In addition, each panel  22  includes a placement pin  22   e  that engages an opening  23  formed through support rings  24  in axial alignment with the slots  24   a  to further ensure accurate alignment of the panels relative to cylinder  26 .  
         [0036]     Each of the elevation receive beam RF signals and the transmitter RF signal from each column are fed into a 24 to 8 electronic matrix that instantaneously selects an 8 column sector and reorders the columns appropriately for the azimuth beamformers. For each azimuth dwell period only 8 of the 24 columns are active. On reception, the azimuth beamformers form an azimuth sum beam and an azimuth difference beam with independent amplitude tapering for optimal sidelobe suppression. The transmit beam is untapered in azimuth.  
         [0037]     Referring to  FIG. 5 , transmit matrix switch assembly  28  includes an azimuth beamformer  28   a  that creates the eight equally weighted transmit signals that form the transmit beam. A matrix switch  28   b  provides beam steering by routing the eight transmit signals to the appropriate eight antenna columns  22  through a 3:1 selector switch  28   c.    
         [0038]     Referring to  FIG. 6 , receive matrix switch assembly  30  works in reverse of transmit matrix  28  and routs received signals from each of the eight active antenna columns  22  through 3:1 selector switch  30   a  and an 8×8 matrix switch  30   b  to an azimuth beamformer  30   c . Azimuth beamformer  30   c  forms sum and difference beams on receipt of signals.  
         [0039]     MCMR  10  has 24 azimuth beam positions 15 degrees apart. The azimuth 3-db beamwidth is slightly wider at 18.7 degrees. A diagram of the 24 azimuth beams is seen in  FIG. 7  and  FIG. 8  depicts the transmit, receive sum, and difference beam patterns in azimuth.  FIG. 9  illustrates the three elevation beam patterns of antenna  12 , i.e., the transmit beam, lower receive beam, and upper receive beam.  
         [0040]     Referring to  FIGS. 10-16 , antenna  12  is constructed on top of tripod  20 . Tripod  20  includes a tri-bracketed connector  36  having thumbwheels for leveling antenna  12  and a boresight scope  38  for aligning antenna  12  in azimuth.  
         [0041]     Antenna cylinder  26  is positioned on tripod  20 . Two (top and bottom) or three (top, bottom, and intermediate) levels of support rings  24  consisting of multiple interlocking panels are mounted around the base, middle, for added stability if needed, and top of antenna cylinder  26 . As seen in  FIG. 11 , support rings  24  have a series of twenty-four circumferentially spaced slots  24   a  for accepting a longitudinal peripheral edge of panel columns  22 . Panel columns  22  are then mounted to support rings  24  using slots  24   a . Once panel columns are in position, a series of ground planes  32  are positioned between adjacent columns  22  by slidingly engaging the peripheral edges into longitudinal slots  22   d . Cable connectors  22   c  of panel columns  22  are then engaged with corresponding connectors  26   a  on antenna cylinder  26  to electrically interconnect antenna electronics of panel columns  22  with transmit matrix switch assembly  26  and receive matrix switch assembly  30  housed within antenna cylinder  26 .  
         [0042]     A small monopole  34  may be placed over antenna  12  (on top of cylinder  26 ) to provide an omnidirectional beam used for sidelobe blanking. Monopole  34  generates a hemispherical pattern with a null at zenith.  
         [0043]     With reference to  FIG. 15 , an antenna connector ring  37  may be used to interconnect antenna cylinder  26  to tri-bracket connector  36 . Connector ring  37  includes brackets  39  that securely receive the thumbwheels of connector  36 , and further includes a circumferential sidewall  41  that envelops the lower portion of cylinder  26 , and a plurality of electrical interconnects  43  and vent openings  45  for connecting cylinder  26  to interface with antenna panels  22 . A base plate includes openings  49  for power cables, data cables, Ethernet cables, and the like. A bubble level  51  provides visual indication of the level of MCMR System  10  relative to the ground.  
         [0044]     As shown in  FIG. 16 , radar electronics comprise a four channel digital receiver  42 , a digital signal processor (DSP)  44 , a coherent waveform generator  46  including local oscillators, and a data processor or CPU  48 . Waveform generator  46  digitally generates a coherent linear FM pulse at 6 MHz IF. The IF waveform is up-converted to L-band using a three-stage up-converter. The output of waveform generator  46  is sent to a transmit matrix module for distribution to appropriate antenna columns  22 . A block diagram for waveform generator  46  is seen in  FIG. 18 .  
         [0045]     Digital receiver  42  uses a double-conversion superheterodyne design with an output IF of 30 MHz. Receiver  42  has four channels: low beam sum, low beam azimuth difference, upper beam sum, and omni. Receiver  42  outputs are fed into a four channel A/D converter card that directly samples the four 30 MHz IF signals with an A/D converter as a sample rate of 24 MHz. The four channels are then converted into a baseband complex signal using a digital downconverter, implemented in a field programmable gate array with an internal clock rate of 144 MHz. The complex data is sent to DSP  44  using high-speed data links. A block diagram for receiver  42  is seen in  FIG. 18 .  
         [0046]     Referring to  FIG. 19 , DSP  44  comprises three high-speed field programmable gate arrays (FPGAs), such as a Xilink Virtex-EM having more than 9 billion usable operations per second. Each FPGA node has 4 Mbytes of 100 MHz static RAM. There are 50 MBPS bi-directional communication links and 50 MBPS data channel loops between each node. A constant false alarm rate (CFAR) detector extracts target detections from the lower sum beam while rejecting clutter and other extraneous returns. Once a detection is declared in the lower sum beam, the corresponding data in the azimuth difference beam, the upper sum beam, and the omni channel are used for azimuth and elevation angle determination and for detecting side-lobe targets. All detection data are sent to the embedded CPU  28  for further processing.  
         [0047]     Embedded CPU  48  is a single board computer that is PC/104 compatible and has four serial channels,  48  digital I/O lines and 10/100 Ethernet networking capability. For example, a WinSystems EBC-TXPLUS configured with an Intel Pentium 166 MHz processor is acceptable. CPU  48  operates the radar. For each multiple-pulse radar dwell, CPU  48  selects that azimuth beam position, chooses the waveform to be transmitted, and receives resulting detections. CPU  48  also processes detection data to provide range and angle sidelobe blanking, monopulse angle measurement, fine range measurement, and single scan correlation. The processed detection data is then sent to laptop computer  16  for additional processing and display.  
         [0048]     Laptop computer  16  is used for radar control and display, as well as data processing. Embedded CPU  48  sends processed detections to laptop  16  for processing by target tracking software. Target track files are maintained on all detected targets. Once sufficient track points are collected on a target, the data is processed by a discriminator that makes an initial determination as to whether the target is a projectile. All targets that discriminate as projectiles are then processed by a trajectory estimator that performs a more detailed target discrimination function to help eliminate false launch point locations from being generated. The trajectory estimator uses a Kalman filter technique to estimate the launch and impact points from the target track data. The target detections, track, launch points, and impact points are all displayed on a PPI display on laptop  16 .  
         [0049]     Power for MCMR system  10  may be provided by a conventional AC-DC power supply  18   a  singularly or in conjunction with portable battery/generator  18 .  
         [0050]      FIG. 20  illustrates the interconnection of the various hardware comprising MCMR  10 , such as antenna columns  22 , laptop  16 , power source (e.g., battery box)  18 , and receiver-signal processor  14  housed in antenna cylinder  26 . Programmable firmware and software operations occur largely in digital signal processor  44  and laptop  16 , and are discussed in greater detail hereafter.  
         [0051]     Referring to  FIG. 21 , digital signal processor  44  comprises a series of firmware operations including a discrete Hilbert transform (DHT)  50 , a time domain correlator (TDC)  52 , a Doppler filter (DOP)  54 , and target detection (DET)  56 .  
         [0052]     Discrete Hilbert transform performs digital down conversion and filtering. An integrated FPGA converts the digital IF data to complex in-phase and quadrature data using a digital complex demodulator and pass band filter. The filter may be changed by loading a different set of filter coefficients in a configuration file. Acceptable MCMR System  10  filter characteristics are listed below in Table 1.  
                                             TABLE 1                                   Parameter   Value                                        Input IF   6.0   MHz           Pass band   0.375   MHz           Pass band weight   1.0           Pass band ripple   −0.21   dB           Stop band   0.675   MHz           Stop band weight   20.0           Stop band ripple   −60.99   dB                      
 
         [0053]     Time domain correlator  52  takes the received data and correlates it against a stored replica or the transmitted pulse, the equivalent of using a matched filter. Because all MCMR waveforms use linear FM coding with a 1 MHz excursion, this operation results in a compressed pulse width of approximately 1 microsecond.  
         [0054]     Doppler filter (DOP)  54  is carried out using a 128 or 256 point FFT operation. The number of points in the FFT is equal to the number of pulses in a radar dwell. In normal operation, MCMR  10  uses 128 or 256 pulses per dwell. However, other dwell modes, such as 512 or 1024 pulses, are available for use. The two-dimensional array of range-Doppler cell data generated by Doppler filter  54  is stored in memory and accessed by target detection module  56 . Parameters for Doppler filter  54  for three commonly used PRI dwells are listed in Table 2 below.  
                                             TABLE 2                               Maximum   Doppler Filter           Number of Pulses   Unambiguous   Bandwidth       PRI (microseconds)   per dwell   Velocity   (Hz)                                50   128   +/−1154   156.250       50   256   +/−1154   78.125       100   256   +/−577   39.063                  
 
         [0055]     Target detector  56  is accomplished by using a sliding window constant false alarm (CFAR) detector. CFAR detector options are show in Table 3 below. Detector  56  also carries out bump detection in both range and Doppler to reduce the number of detections cause by large targets.  
                               TABLE 3                                   Parameter   Options   MCMR Setting                           Target cell position   Leading, center,   Center               trailing           CFAR dimension   Range, Doppler   Range           CFAR length   4, 8, 16, 32, 64, 128,   32               256                      
 
         [0056]     Referring to  FIG. 22 , software installed on laptop  16  provides radar control, data processing, information display, data recording, and playback capabilities. It should be understood that a variety of software implementations are possible for managing and displaying the reading obtained by MCMR  10 . Similarly, a variety of graphical user interfaces are possible for enhancing user operation of MCMR  10 . For example, custom windows may be designed for the entry of radar parameters and controls as well as turning the radar on and off. Similarly, software may provide a plan position indicator (PPI) display for tracking relative motion of targets, an oscilloscope display for visualizing the contents of DSP  44  memory, or a waterfall display of historical parameters and targets detected by MCMR  10 .