Advanced Radar Systems

1. Advanced Radar Systems

2. Objectives • Describe how a Pulsed Doppler radar works and how it’s able to determine target velocity. • Describe how a Moving Target Indicator (MTI) determines target velocity. • Describe how a pulse compression can provide a high-resolution radar return at the receiver.

3. Velocity Determination for Pulse Radars • Basic Pulse Radar system cannot determine velocity directly from a single pulse. • However, radar modifications enable us to determine movement

4. Advanced Radar Systems • Combine the ranging feature of Pulse radars with the range rate feature of CW radars • Range, bearing, elevation to target • Detects target’s velocity • Uses radial velocity to eliminate stationary returns (clutter) or compute their velocity and future location • Two types: Moving Target Indicator (MTI) and Pulse Doppler (PD) • MTI uses phase measurements to ID moving targets • PD uses frequency measurements to ID moving targets and compute velocity in LOS

5. Moving Target Indicator (MTI) • Compare transmitted phase to return phase to detect motion (i.e., phase shift) • usesphase comparator • One full cycle of phase shift (360 degs) equals a change in range of ½ l • pulse-to-pulse comparisons; resulting phase measurements are averaged to discriminate between moving targets and stationary ones • cancellation circuit eliminates non-zero phase average(Clutter Rejection) • Bearing, Range, and Motion • Primarily used in Search Radar systems

6. Δphase Pulse 1 time Pulse 2 Pulse 3 Pulse 4 Pulse 5 Next Pulse Avg Phase Difference Subtracted Displayed Signal Only moving Displayed

7. Moving Target Indicator (MTI) • Delay line circuit saves previous phase evaluation for comparison. • Cancellation circuit subtracts previous phase comparison from current phase comparison. • Return from Stationary targets will have same phase comparison and be cancelled out. • Return from Moving targets will have different phase comparison and will be retained / displayed.

8. MTI

9. Pulse Doppler • Attributes of pulse radar / technology of CW radar. • Why is a “mixer” added to Pulse Radar? • Sample of transmitted and received signal compared at mixer. • Mixer output is Doppler shift (velocity). • Doppler sorted into velocity categories. • In some applications velocities are coded by color. • Standard Weather Radar. • More rain / higher wind – higher Doppler.

10. Hurricane Isabel- Photo

11. Hurricane Isabel – Pulse Doppler

12. Pulse Doppler Radar • Principle military use as Fire Control Radar • High PRF • Many pulses / high frequency gives large amount of range and range rate data • High degree of accuracy • (range, bearing, elevation, velocity) • Target position now includes velocity • Large receiver Bandwidth (BW) to capture larger fD

13. ft Transmitter Mixer fr Receiver Df Antenna Doppler Filter Display Pulse Doppler System

14. High Resolution Radar • Pulse Compression • Synthetic Aperture Radar (SAR) • Inverse Synthetic Aperture Radar (ISAR)

15. Pulse Compression • Signal Processing Technique. • Same idea as FMCW • Except in a pulse • Combines: • High energy of Long Pulse. • High resolution of Short Pulse. • Pulse is Frequency Modulated. • Increased in frequency over duration of pulse.

16. Pulse Compression Distance between Leading Edge Remains Same • Return pulse passed thru Pulse Compression Circuit. • Lower frequencies pass through slower. • Pulse “piles up” on itself. • Can distinguish multiple returns within PW • Filter Output is a signal with: • greater power for longer range. • narrower pulse width

17. Pulse Compression Transmitted Pulse Received Pulse

18. Pulse Compression Filtering

19. Objectives • Describe how a Pulsed Doppler radar works and how it’s able to determine target velocity. • Describe how a Moving Target Indicator (MTI) determines target velocity. • Describe how a pulse compression can provide a high-resolution radar return at the receiver.

20. Assignment • Reading Assignment pp 4-16 to 4-18. • Do Guided Reading • Problem Set 2