Bài giảng Định vị và dẫn điện tử - Chương 6

Nguyên lý và hệ thống Radar Radar Principles &Systems ξ 9. Tự động bám mục tiêu radar Màn hình hiển thị nhìn vòng PPI Radar Screen 10 20 30 40 Primary Radar Display Màn hình hiển thị mục tiêu radar STARS ARTS ARTS: Automated Radar Terminal System STARS: Standard Terminal Automation Replacement System - Provides Operational information about aircraft positions, flight data, and weather. - Allows technical operations personnel to monitor and control system resources. STARS Standard Terminal Automation Replacement System STARS Standard Terminal Automation Replacement System Tracking Terms Tracking Element Line-o f-Sight Tracking Line Error Limitations of Mechanical Scanning Radars  Positioning Antenna is SLOW  Reduced reaction times  Blind Sided!  Mechanical error Electronic Scanning • Increased Data Rates • Instantaneous Beam Positioning • Elimination of Mechanical Errors • Multi-mode Operation • Multi-target capability Phased Array Generating a Directional Main Lobe in a Phased Array Radar Altering the Phase to Change the Axis Boresight Axis Bea m A xis Radiating in Phase Boresight Axis Wave Fronts of Maximum Energy (a) (b) (c) Basic phased array architecture FoV: Field of View <= 1200 Phase-increment Calculating d = distance between the radiating elements Θ= beam steering x    0360      sin360d  )sin (θdx   x Phase-increment. Example A phased array radar unit including 8 elements works with a wavelength of λ=10 cm. The distance between the radiating elements is 15 cm. We can neglect the propagation time differences by the feeder. The beam steering shall be Θ= 40°. • Which value shall have to have the phase shifter no. 8 (on the left side) to get this beam steering? Phased Array  In radar applications, phased arrays permit near instant switching from one target to another, and from search to track mode. Typical air-to-air search pattern 300 300 100 -120 Air-to-air tracking Phase Array Radar (scanning diversity;multi-mission*; etc.) *ARSR;ASR;TDWR;WR Basic Principle: Target energy return is strongest on the axis of the beam, diminishes further from the axis. axi s Methods of Tracking: * Sequential Lobing * Conical Scan * Monopulse Nguyên tắc bám mục tiêu Sequential Lobing L L LR R R Antenna looking left of target Antenna Pointing directly at target Antenna looking right of target Return Signals form Two Beams * Simplest Method * Multiple Beams * Compare Returns * Relatively Slow * Still used by some countries Conical Scanning * Rotates a beam in a circle producing a cone of energy. Antenna Lobe Of Energy Pattern of scanning Locus of Beam Centers Beam Time Pulse Return Amplitude Equal Amplitude Sensor Return Signal Antenna Axis Target Position is in the Center of the Conical Scan (On Antenna Axis) Determining Tracking Error Using Conical Scan Determining Tracking Error Using Conical Scan Locus of Beam Centers Beam Time Pulse Return Amplitude Varying Amplitude Sensor Return Signal Antenna Axis Target Position Off the Center of the Antenna Axis Monopulse radar Monopulse radars are similar in general construction to conical scanning systems, but add one more feature. Instead of broadcasting the signal out of the antenna "as is", they split the beam into parts and then send the two signals out of the antenna in slightly different directions. When the reflected signals are received they are amplified separately and compared to each other, indicating which direction has a stronger return, and thus the general direction of the target relative to the boresight. Since this comparison is carried out during one pulse, which is typically a few microseconds, changes in target position or heading will have no effect on the comparison. Partial antenna patterns for amplitude sum and difference monopulse system Monopulse antenna beam patterns The angle between the axis of the antenna (boresight axis) and the direction of the target is also known as OBA-value (Off-Boresight Angle). Độ chính xác bám mục tiêu Tracking accuracy SNR   2     Độ rộng búp sóng radar Sai số đo độ lệch góc Example TRACK-WHILE-SCAN TWS CONCEPT • Radar scans continually • Computer maintains target tracks –Receives periodic radar scan updates –Builds track history –Predicts positions • TWS = Track-While-Scan!! Maintain target tracks in a computer with periodic information from a scanning radar. KEY TO TWS IS: GATE GENERATION • Acquisition gate • Tracking gate • Turning detection gate * Gates are 3-dimensional pieces of space that the target occupies. * Size of Gates are determined by the computer based on the information. ACQUISITION GATE 10 degrees 10 degrees 2000 yards TRACKING GATE 1.5 degrees 1.5 degrees 120 yards TURN DETECTION GATE Computer determines gate size tracking gate TWS PROCESSING Acquisition Gate Tracking Gates Turn Detection Gate Original Course New Course Air-to-air TWS