All weather tactical strike system (AWTSS) and method of operation

• US 5,245,347 A
• Filed: 12/29/1980
• Issued: 09/14/1993
• Est. Priority Date: 12/29/1980
• Status: Expired due to Fees

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Bonta, Gerald A., Peregrim, Theodore J., Mangiapane, Rosario, Ogar, George W.
• Primary Examiner(s): TARCZA, THOMAS H
• Application Number:
  US06/234,043
• Time in Patent Office: 4,642 Days
• Field of Search: 343/16 M, 343/5 FT, 343/5 NQ, 342/149, 342/194, 342/196
• US Class Current: 342/149
• CPC Class Codes: G01S 13/44 Monopulse radar, i.e. simultaneous lobing
• CPC Class Codes: G01S 13/86 Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 13/9092 combined with monopulse techniques
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures
• CPC Class Codes: G01S 7/403 in azimuth, i.e. in the horizontal plane
• CPC Class Codes: G01S 7/4034 in elevation, i.e. in the vertical plane
• CPC Class Codes: G01S 7/4065 involving a delay line
• CPC Class Codes: G01S 7/4069 involving a RF signal injection
• CPC Class Codes: G01S 7/4078 involving an integrated reference reflector or reference transponder

Abstract

An AWTSS is shown to be made up of an improved synthetic aperture radar (SAR) for generating radar maps with various degrees of resolution required for navigation of an aircraft and detection of ground targets in the presence of electronic countermeasures and clutter. The SAR consists, in effect, of four frequency-agile radars sharing quadrants of a single array antenna mounted within a radome on a "four axis" gimbal with a sidelobe cancelling subarray mounted at the phase center of each quadrant. Motion sensors are also mounted on the single array antenna to provide signals for compensating for vibration and stored compensating signals are used to compensate for radomeinduced errors. In addition, a signal processor is shown which is selectively operable to generate radar maps of any one of a number of desired degrees of resolution, such processor being adapted to operate in the presence of clutter or jamming signals.

Claims

1. The method of operating an airborne synthetic aperture monopulse radar having an antenna with four quadrants arranged in the form of a diamond such that the phase centers of two of such quadrants lie in the slant plane determined by the aircraft velocity vector and the line-of-sight vector to a ground reference point and the phase centers of the remaining two quadrants lie in a plane orthogonal to the slant plane, to allow, in the presence of competing ground clutter, the angular separation of moving targets spaced from boresight to be determined, such method comprising the steps of:

(a) separately processing echo signals received in each one of the four quadrants from targets at substantially equal range to form a set of complex digital numbers indicative of the amplitude and phase of the echo signals at each one of the quadrant phase centers;

(b) multiplying each complex digital number in each one of the four sets thereof by a compensating factor to linearize the change in phase between successive complex digital numbers in each set thereof to form four compensated sets of complex digital numbers;

(c) storing the four compensated sets of complex digital numbers and then retrieving such numbers;

(d) processing the compensated sets of complex digital numbers by a fast Fourier transform to arrange such complex digital numbers in a range/Doppler matrix;

(e) computing, from knowledge of the Doppler frequency associated with each cell, the angular location of potential target cells in the range/Doppler matrix;

(f) combining the compensated complex digital numbers from the two antenna quadrants whose phase centers lie in the plane orthogonal to the slant plane to form a third phase center in the slant plane;

(g) forming a pair of monopulse difference pattern nulls from the compensated sets of complex digital numbers corresponding to the three phase centers in the slant plane;

(h) shifting the pair of difference pattern nulls to place both nulls on the potential target cell;

(i) testing the potential target cell for residual energy due to the motion of a moving target spaced from boresight;

(j) estimating the angular location of such moving target;

(k) shifting one of the difference pattern nulls to the estimated location of the moving target; and

(l) repeating steps (i) through (k) until the residual energy within the potential target cell falls to the level of the null at which time the moving target is unambiguously located in angle.