Patent Publication Number: US-7719458-B1

Title: Dual mode weather and air surveillance radar system

Description:
This application is a continuation of application Ser. No. 11/300,908, filed Dec. 15, 2005, and claims priority thereto and the benefit thereof under 35 U.S.C. §120. 
    
    
     BACKGROUND 
     1. Field 
     The present invention relates generally to radar systems, and, in particular, to radar systems having dual modes, and still more particularly, to radar systems having a weather radar mode and an air surveillance mode. 
     2. Description of the Related Art 
     Since the invention of detection and ranging using radio frequencies, different radar systems have been developed to meet the requirements of detecting different phenomena or objects. All radars work on the same basic principles of transmission of RF energy into the transmission medium (for example, the atmosphere), reception of reflected energy, (also known as backscatter or return energy), and analysis of the received energy to determine the presence and possibly characteristics of the detected object(s). Each type of radar system is optimized for the targets sought to be detected by the radar. 
     For example, weather radar systems are tailored to detect airborne precipitation, known in the art as hydrometeors. Many weather radars operate in the radar frequency bands and wavelengths that require large antennas and may preferably be horizontally polarized to better detect falling hydrometeors. On the other hand, other radars, for example, air surveillance radars tend to be horizontally linearly, and may be circularly polarized in order to reject returns due to weather in the scan volume. Analysis of the return energy has long been performed by computer processors configured with software that is specifically developed to process the data represented by the received energy. 
     Being able to detect both weather and air targets meant multiple radar systems, i.e., a weather radar and a separate air surveillance radar, co-located at or near a site of interest. Each separate system would mean installation and operation of separate hardware (antenna, transmitter, receiver, computer processors, power supplies and displays), and separate software modules installed in those systems. This requires sufficient space to install and operate such hardware. It also results in increased costs for the hardware and its maintenance. 
     Multi-mode radars have been developed to provide detection capability of differing object types in a limited space. For instance, modern fighter aircraft (third generation and beyond) employ radars with multi-mode capability. There is an air-to-air radar for detection of airborne targets, and an air-to-ground radar for air-to-surface weapons targeting. The former may be pulsed, doppler, or pulsed-doppler, while the latter may be a pulse only synthetic aperture radar. There have been radars fielded that incorporate two antennae; one for search and detection, and the second for weapons guidance. 
     These radars however are only examples of achieving multi-mode capability in the confines of a small air platform. Heretofore, there is not a successfully deployed multi-mode radar for use at air fields, for example, that need a weather radar in addition to air surveillance capability. 
     SUMMARY 
     The present disclosure is directed to dual mode radar system that may operate in, for example, a weather detection mode or an air surveillance mode. For purposes of summarizing the invention, certain aspects, advantages, and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any one particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     The below described invention is for a radar system that can operate in two modes, for example, weather detection and air surveillance. The system comprises a dual antenna assembly comprising first and second antennae that have respective first and second antenna waveguides coupled to a waveguide switch. The waveguide switch diverts RF energy to or from either antenna waveguide and is coupled to a common waveguide that extends from a pedestal supporting the dual antenna assembly. The first and second antennae are designed for use in said first and second modes respectively. 
     The pedestal whereupon said antenna support assembly is pivotally mounted with respect to the vertical plane comprises an azimuth section and an elevation section that have respective azimuth and elevation drive means for rotating said antenna support assembly in two planes and respective position indicating means for determining azimuth and elevation angle of the dual antenna assembly. The system includes a control processor configured with control logic operable to control the functions of the radar system. The first and second antennae are mounted generally perpendicularly in the vertical plane with respect to each other and the radar system operates in only one of said modes of operation at any time. 
     An objective of the present invention is to provide a radar system that can operate in two modes, but occupy a minimum space, and maximize the use of common components, thus reducing costs required for parts and maintenance. 
     These and other embodiments of the present invention will also become readily apparent to those skilled in the art from the following detailed description of the embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
         FIG. 1  is a block diagram of the dual mode radar system according to an embodiment of the present invention; 
         FIG. 2  is a block diagram of the microwave subsystem of the dual mode radar according to an embodiment of the present invention; 
         FIG. 3  is a block diagram of the receive subsystem of the dual mode radar according to an embodiment of the present invention; 
         FIG. 4  illustrates a pedestal for use in the dual mode radar system, with cut-away sections, according to one embodiment of the present invention; 
         FIG. 5A  is a perspective view of the antenna pedestal with dual antenna mounted thereon depicting a first operational mode according to an embodiment of the present invention; 
         FIG. 5B  is a second perspective view of the antenna pedestal with dual antenna mounted thereon depicting a second operational mode according to an embodiment of the present invention; and 
         FIG. 5C  is a schematic view of the dual antenna according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments of the present invention and their advantages are best understood by referring to  FIGS. 1 through 5  of the drawings. The elements of the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. Throughout the drawings, like numerals are used for like and corresponding parts of the various drawings. 
     This invention may be provided in other specific forms and embodiments without departing from the essential characteristics as described herein. The embodiments described above are to be considered in all aspects as illustrative only and not restrictive in any manner. The appended claims rather than the foregoing description indicate the scope of the invention. 
     With reference to  FIG. 1 , an exemplary dual mode weather and air surveillance radar system  100  comprises a transmitter  101  having an output coupled to a duplexer  103 . Duplexer  103  is further coupled to a transmit output  106  and to an output that is a receive output  108 . Transmit output  106  is coupled to dual antenna assembly  111  through microwave subsystem  107 . Receive output  108  is coupled to a receive subsystem  105 . Receive subsystem  105  has a received signal output  102  that is coupled to radar data and control processor  113 . 
     As discussed and shown in greater detail below, dual antenna assembly  111  comprises both an antenna optimized for weather observation and an antenna designed for air surveillance. Dual antenna assembly  111  is mounted on pedestal  109  which includes drive means  121  that drives rotation of dual antenna assembly  111  in either mode as would be understood by those skilled in the relevant arts. Dual antenna assembly  111  is pivotally mounted upon the pedestal  109  with respect to a vertical plane with means for varying the antenna&#39;s elevation coupled thereto. Pedestal  109  may also antenna azimuth and elevation reading means  123  which operate to determine the angular position of antenna  111 , and relay that data to control processor  113 . 
     Transmitter  101  may be an electromagnetic signal transmitter capable of transmitting at a pulse repetition frequency (PRF) of about 250 to about 1180 pps. Preferably, transmitter is also capable of emitting in controllably variable pulse widths. For example, pulse widths may range from about 0.4 to about 2.0 μs. The pulse width may be set by a control circuit. A solid state modulator that is also pulsewidth agile may also be used. The modulator provides a high-power pulse of about 26 kV to about 28 kV at the cathode of the magnetron, thus causing the magnetron to oscillate at the proper frequency under the selected pulse width. Transmitter  101  may also include a magnetron which may operate at about 5300 MHz to about 5800 MHz. As would be appreciated by those skilled in the art, the magnetron generates the radio frequency (RF) energy that is fired to transmit a pulse. 
     Microwave subsystem  107  is described in greater detail with reference to  FIG. 2  where there is depicted, transmitter  101  coupled to duplexer  103  as described above. Duplexer  103  has a transmit output  106  that is coupled to microwave subsystem  107  which is comprised of a tuner having an output that may be coupled to filter  223  before it is coupled to antenna system. Microwave subsystem  107  also advantageously may comprise an automatic frequency control (AFC) subsystem  231  which further comprises sampler  215  coupled to the transmit feed line and having an output coupled to an input to mixer  217 . Mixer  217  has a second input from a stable local oscillator  235  and an output coupled to an analog-to-digital converter (ADC)  241 . 
     In operation, transmit energy output  106  from duplexer  103  is applied to tuner  221  which adjusts signal power in the event there exists a difference between reflected power (VSWR) in the waveguide and transmitted power. Preferably, tolerances for operation of tuner  221  should result in a ratio between reflected power and transmitted power of less than 1.1 to 1. Transmit energy may then be applied to a filter  223 , preferably a lowpass filter. In one embodiment, filter  223  passes a band between about 5300 MHz to about 5800 MHz to avoid interference with neighboring C-band emitters/receivers. Other filtering may be used in lieu of, or in conjunction with bandpass filter to achieve desired signal spectra as would be appreciated by those skilled in the arts. Transmit energy from filter  223  is guided to rotary waveguide couplers mounted in the pedestal to direct the transmitted energy to the dual-mode antenna in. 
     Concurrently, automatic frequency control subsystem  231  provides control of receive subsystem frequency by sampler  215  routing sample signals  210 , which are RF transmit sample signals from the transmitter output  106  to AFC subsystem  231 . The sample signal  210  is preferably about −80 dBm of the 350 kilowatt pulse. Sample signal  210  is applied to mixer  217  to which is also applied a local oscillator signal  234  output from a stable local oscillator (STALO)  235 . The mixer  217  heterodynes RF transmit sample  210  with STALO signal  234  to produce a burst pulse signal  236  that is phase-coherent with the transmitter signal  106 . Burst pulse signal  236  is then coupled to ADC  241  and converted to a digital burst signal  240  representing the phase-coherent frequency and phase information. Digital burst signal  240  is received by the signal processor  245  which measures the digital burst signal. If the frequency of digital burst signal  240  is not within some delta of the frequency of STALO signal  234  (for example, within +/−10 KHz of STALO signal  234 ), signal processor  234  generates a control signal  250  that is applied to an automatic frequency control circuit, discussed and shown in greater detail below. The control signal  250  is processed to produce a digital error signal to the STALO to ensure desired separation between the transmitted RF frequency and the STALO RF frequency. 
     Duplexer  103  allows the radar system to both transmit and receive RF energy using a single antenna (i.e., monostatic radar). Duplexer  103  preferably provides at least about 25 dB of isolation between the transmitted and received RF signals. Duplexer  103  may be achieved with a “4-port circulator” wherein transmitted energy enters the 4-port circulator at a first port  1  (“port  1 ”), and exits at a second port (“port  2 ”). Received energy enters the 4-port circulator at port  2  and is fed to the receiver subsystem  105  via a third “port  1 ”. If VSWR occurring in the waveguide transmission line does not match the transmitted power, it is fed to a dummy load coupled to “port  4 ” of the 4-port circulator. Port  1  may be equipped with a forward power coupler, which is used to measure transmitted power. Similarly, port  4  may be equipped with a reflected power coupler and used to measure reflected power. 
     The receive subsystem  105  is discussed in detail with reference to  FIG. 3  beginning with duplexer  103  which is has a receive energy output  108  coupled to a protector  331 . Protector  331  is coupled to an amplifier  333  which is preferably a low noise amplifier (LNA). LNA  333  is then coupled to a signal mixer  325 . Signal mixer  325  also has a input signal from a stabilized STALO  235  which may be achieved by using the same STALO as that described with reference to  FIG. 2 . Signal mixer  325  has an output coupled to a buffer amplifier  327  which is coupled to ADC  241  which also may be the ADC described with reference to  FIG. 2 . ADC  241  also has an output that is coupled to digital signal processor  245 . 
     Backscatter energy captured by the antenna is coupled back through waveguide to the duplexer  103  receiver port. Duplexer  103  receive output  108  is coupled to receiver protector  331  which acts as a transmit/receive switch and blocks transmitted pulses from the receive subsystem. Protector  331  measures energy applied through the system at the receive output port of duplexer  103 . If such energy is greater than VSWR (reflected energy) then protector  331  blocks such energy from the remainder of the receive subsystem  105 . If such energy is less than VSWR, then protector  331  allows this energy to be applied to the remainder of receive subsystem  105 . Protector  331  output  326  is then preferably coupled to a low noise amplifier (LNA)  333  which in one embodiment is configured to operate with a low noise figure of about 1.3 dB. Preferably, the pass band of the LNA is between about 5300 MHz to about 5800 MHz. The saturated output power (1 dB compression) of the LNA is preferably +13 dBm. LNA output is a received RE signal  332 . 
     Received RF signal  332  is coupled to a signal mixer  335  which also receives as input the output a STALO signal  334  from STALO  235 . STALO signal  334  is mixed with the received RF signal  332  to generate a received IF signal  338 . Received IF signal  338  is coupled to ADC  241 , preferably via buffer amplifier  337  which may be used to set the linear range of the receiver to about 93 dBm. ADC  241  converts received IF signal  338  to a digital received signal  342  which is coupled to signal processor  245  for processing. 
     Radar data and control processor  113  may be configured to provide the functions described as being performed by signal processor  245  as would be appreciated by those skilled in the relevant arts. Radar data and control processor  113  is a processor that is configured with control logic to provide signal control and analysis of both transmitted and received radar energy. Further, it may be configured with control logic provide control signals to direct movement of antenna in both rotation and elevational position. 
     Pedestal  109  provides a stand upon which antenna is mounted in addition to housing for antenna drive and control means as well as wave guide structures to port the RF energy to and from antenna  111 . With reference now to  FIG. 4 , pedestal  109  may be provided in two sections. The depicted embodiment is known in the art as an “elevation-over-azimuth” arrangement because it comprises an azimuth drive and control section  401  at the base and an elevation drive and control section  403  above it. Azimuth section  401  is a generally cylindrical housing for azimuth drive motor  407  which is rotationally engaged with azimuth turntable  409  via reduction gears (not shown), as would be understood by those skilled in the art. Azimuth turntable  409  is secured to azimuth section  401  in a manner to allow free rotation thereof. Also rotationally engaged with azimuth turntable  409  is azimuth position reader  411 . 
     Elevation section  403  is mounted to azimuth turntable  409 , and similarly is a generally cylindrical housing for elevation drive motor  417  which is rotationally engaged with elevation driving turntable  419  via reduction gears (not shown), as would be understood by those skilled in the art. Also, rotationally engaged with elevation driving turntable  419  is elevation position reader  421 . Elevation turntable  419  is disposed external to the housing and is secured thereto in a manner that allows rotation of the turntable  419  in the vertical plane. 
     Also housed within pedestal  109  is waveguide structure  123  which is comprised of a lower rotary coupler  404  coupled to vertical waveguide  402 . Vertical waveguide  402  extends the length of the azimuth section through azimuth turntable  409  and into elevation section where it is coupled to flexible waveguide  406 . Vertical waveguide  402  may be coupled to flexible waveguide  406  by means of rotary couplers (not shown) as would be understood by those skilled in the relevant arts. Flexible waveguide is bent at about ninety degrees and extends through elevation section wall through a turning bearing  425  to an upper rotary coupler  408 . Turning bearing  425  is secured to elevation section housing  403  in a manner that allows rotation of the bearing  425  in the vertical plane. 
     Mounted to both elevation turntable  419  and turning bearing  425  is antenna support assembly  450  comprised of an antenna mounting platform  451  which is affixed to opposing support arms  453 ,  454 . A counter-weight assembly  452  may be attached to at least one support arm. Although not shown in the Figure, dual antenna assembly  111  is fixedly mounted to antenna support platform  451 . 
     Azimuth and elevation drive motors  407 ,  417  may be electric DC motors that drive planetary reduction gears engaged with the turntables  409 ,  419 . Azimuth section  401  may be configured to drive rotation of the azimuth turntable  409  through 360°, i.e. no mechanical or other limits. Because the elevation section  403  is fixedly mounted to the azimuth turntable  409 , it rotates with the azimuth turntable  409 . Operation of azimuth drive motor  407  is configured to be controlled by radar data/control processor  113 . Concurrently, elevation drive motor  417  rotates elevation turntable  419  in like manner, with control provided by radar data/control processor, and consequently the antenna support assembly, with dual antenna mounted thereon is rotated in the vertical axis; however, its rotation must be limited. This may be achieved with electrical limit switches, limits encoded within control logic resident in the radar data/control processor  113 , as well as buffered mechanical stops. For example, in one embodiment, control logic limits may command reversal of antenna assembly vertical rotation when antenna vertical position reaches a lower limit of −4° and an upper limit of +94°. As a back-up, electrical limit switches may be configured to activate with an antenna vertical position lower limit of −4° and an upper limit of +94°. Finally, in the event that both the control logic and electrical switch limiters fail, shock-absorbing mechanical stops may be affixed to the elevation section housing that physically arrest vertical rotation of the antenna assembly at a lower limit of −5° and an upper limit of +95°. 
     Azimuth and elevation position readers  411 ,  421  are known as “encoders” in the art that serve to determine the antenna&#39;s angular position in the horizontal and vertical planes of rotation respectively, during scanning operations and provide that data to radar data/control processor  113 . 
       FIGS. 5A-C  depict various aspects of dual antenna assembly  111  comprises a weather (WX) antenna  517  co-mounted with an air surveillance (AS) antenna  519 . Weather antenna  517  may be any suitable parabolic reflector with any polarization technique. Preferably, WX antenna  517  is configured for horizontal polarization in order to best capture hydrometeors. WX antenna  517  optimally produces a circular pencil beam with a gain of 40 dB and a beamwidth of 1.5 degrees which allows WX antenna to couple a narrow focused beam into the air to capture precipitation backscatter. 
     AS antenna  519  may be any suitable antenna designed for air surveillance. For example, in one embodiment, AS antenna is a specialized sectioned parabola that generates a pseudo-cosecant 2  beam shape having an azimuthal beamwidth of 1.6 degrees and an elevational beamwidth of 30 degrees. Circularly polarized transmitted energy rolls off at a cosecant rate from maximum gain to minimum gain as a function of the elevation angle, as would be appreciated by those skilled in the relevant art, such that a constant power illuminates aircraft when flying at a constant altitude. This constant power characteristic of the AS antenna and the measured signal-to-noise ratio of the return may be employed by the system to estimate the size of the aircraft. The AS antenna preferably operates with circular polarization to aide in eliminating returns from weather formations, i.e. rain. This allows the radar to acquire aircraft and plot them on the displays even when the detected aircraft passes through weather. 
     WX and AS antennas  517 ,  519  are preferably oriented substantially reciprocally (about 180° apart), facing away from each other in the horizontal plane. It is further preferable to mount antennas  517 ,  519  roughly perpendicularly with respect to the other in the vertical plane, mounted to adjacent perpendicular portions of antenna mounting bracket  521  which is secured to antenna support assembly  450  from  FIG. 4 . External waveguide  502  is coupled to upper rotary coupler  408  (shown in  FIG. 4 ) and is coupled at its opposite end to waveguide switch  504  from which extends WX antenna waveguide  506  and AS antenna waveguide  508 . WX waveguide  506  is ultimately coupled to WX antenna feed horn  511  and, likewise, AS waveguide  508  couples to AS antenna feed horn  513 . It should be noted that depending upon the size of the two antennas, one antenna may be altered to accommodate the other. For instance, in one embodiment depicted in  FIG. 5A , the top of the AS antenna  519  reflector includes a recess that conforms to the back of the WX antenna  517  reflector. 
     When radar system is in a weather mode, WX antenna  517  is in a deployed position with its beam centered at an elevation of roughly one half of the 3 Db beamwidth above the horizon and AS antenna  519  is in the stowed position (roughly +90° elevation), shown in  FIG. 5B . Antenna  111  is driven by motors in pedestal  109  to rotate in azimuth and/or elevation. During weather mode, waveguide switch  504  is open to divert RF from external waveguide  502  to WX waveguide  506  and thence to WX feedhorn  511 . When desired or required, the system may be converted to air surveillance mode where WX antenna  517  is rotated to the stowed position and the AS antenna  519  is rotated to the deployed position for scanning (shown in  FIG. 5A ). Concurrently, waveguide switch  504  is commanded to flip, diverting RF energy from external waveguide  502  to AS waveguide  508  and thence to AS feedhorn  513 . At the same time, the processor signal analysis functions switch from a weather scanning mode to an air surveillance mode. Conversion back to weather mode simply reverses the process. Preferably, when the antennas are switched, the previously stowed antenna is not only driven to depart from the +90° position to scanning elevation, but also to slued in azimuth to the same azimuth angle where the previously deployed antenna was when the mode switch was initiated. 
     Control processor  113  provides control over all radar system functions described above and is configured with control logic which causes processor to implement necessary control commands. Control of antenna positioning and modes is also provided by control processor  113  as suggested above, and specifically, control of the tasks for conversion from one mode to the other is provided by control processor including the switching of antennas and the flipping of the waveguide switch. It is well-known that in signal processing, reflected energy is processed in a manner that determines the bearing, altitude and range of the source of the reflection from the site. Antenna azimuth and elevation angle must be known in order to determine the bearing from where reflected energy is received. As described above, antenna position data is relayed to control processor  113  by the respective position indicators, or encoders  411 ,  421 . 
     Scanning may be performed in a variety of ways depending upon the desires of the operator. When in weather mode, the scanning may be a conventional volumetric scan conducted beginning with a preset +0.8° (half of the beamwidth) elevation and an elevation step-up equal to the beam width after every 360° of rotation until the full volume desired is scanned. The scan rate of the system, depending upon the drive motors, is preferably from 0 to about 6 rpm. The system may be configured with control logic to initiate a mode change to air surveillance automatically. For example, in one embodiment, the radar could maintain a weather scan to cover the full scan volume, and then control logic could command the system to change modes and search for airborne targets for its entire scan volume. In a further embodiment, the system could remain in air surveillance mode for a desired period of time, e.g., 30 minutes, 1 hour, 4 hours, and so on, and programmed to automatically switch to weather mode. The system could then complete a full weather scan, and then return to air surveillance mode. This is advantageous in situations when weather is not expected, or is slowly changing, therefore, information about the weather need not be updated as frequently. 
     It should be noted that although they are not described above, the radar system could further comprise operator stations with displays and controls for operator interface. Any such stations would also be controlled by the radar control processor. A display could be used for both modes. Such a display may be configured with control logic, through the control processor or separately, such that it will be display optimized for the first mode, and then change along with the switching of modes to a display optimized for the second mode as would be appreciated by those skilled in the relevant arts. 
     An objective of the dual mode radar system is to provide the functions of a weather radar along with an air surveillance radar in a minimal amount of space. To achieve this objective, the system is preferably configured with one set of encoders. As such, azimuth and elevation data are derived from the position of the antenna support assembly  450 . With respect to elevation angle, the position of the assembly  450  may be accurate for only one of the two antennas  517 ,  519 . Therefore, the elevation angle of the opposing antenna relative to other must be account for in processing. For example, if the system is configured such that the elevation angle of the assembly  450  coincides with the WX antenna  517 , the elevation angle data for the AS antenna  519  when it is scanning will be offset by 90° from the information the encoders provide to the control processor  113 . Control logic resident in the control processor  113  includes computational features that take the offset into account when determining elevation angle of the opposing antenna. 
     Control processor  113  in effect comprises a computer system. Such a computer system includes, for example, one or more processors that are connected to a communication bus. The computer system can also include a main memory, preferably a random access memory (RAM), and can also include a secondary memory. The secondary memory can include, for example, a hard disk drive and/or a removable storage drive. The removable storage drive reads from and/or writes to a removable storage unit in a well-known manner. The removable storage unit, represents a floppy disk, magnetic tape, optical disk, and the like, which is read by and written to by the removable storage drive. The removable storage unit includes a computer usable storage medium having stored therein computer software and/or data. 
     The secondary memory can include other similar means for allowing computer programs or other instructions to be loaded into the computer system. Such means can include, for example, a removable storage unit and an interface. Examples of such can include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, and other removable storage units and interfaces which allow software and data to be transferred from the removable storage unit to the computer system. 
     Control logic (also called computer programs) are stored in the main memory and/or secondary memory. Such computer programs, when executed, enable the computer system to perform certain features of the present invention as discussed herein. In particular, the computer programs, when executed, enable a control processor to perform and/or cause the performance of features of the present invention. Accordingly, such computer programs represent controllers of the computer system of a radar system. 
     In an embodiment where the invention is implemented using software, the software can be stored in a computer program product and loaded into the computer system using the removable storage drive, the memory chips or the communications interface. The control logic (software), when executed by a control processor, causes the control processor to perform certain functions of the invention as described herein. 
     For example, control processor  113  may also be a signal processor which analyzes backscatter energy to determine the extent and intensity of precipitation or whether an aircraft is approaching the radar site. Control processor  113  may therefore be configured with control logic (software) designed to execute functions that process the received RF energy according whichever mode the system is operating in. Such control logic may be provided in software modules. For example, the control processor may be configured with software for the air surveillance mode and software for the weather mode. Obviously, when converting from one mode to another, the system must also stop execution of one software, and initiate execution of the other. 
     In another embodiment, features of the invention are implemented primarily in hardware using, for example, hardware components such as application specific integrated circuits (ASICs) or field-programmable gated arrays (FPGAs). Implementation of the hardware state machine so as to perform the functions described herein will be apparent to persons skilled in the relevant art(s). In yet another embodiment, features of the invention can be implemented using a combination of both hardware and software. 
     As described above and shown in the associated drawings, the present invention comprises an apparatus for a dual mode weather and air surveillance radar system. While particular embodiments of the invention have been described, it will be understood, however, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. It is, therefore, contemplated by the following claims to cover any such modifications that incorporate those features or those improvements that embody the spirit and scope of the present invention.