6. June 17, 2010Digital MultiBeam Radar6
Radar Fundamentals (1)
Pulse radar
• Range :
• Example: t = 100 µs → R = 15 km
• Range resolution :
• Example: τ = 10 ns → ∆R = 1.5 m
Transmitted pulse Echo pulse
Time delay (t)
Pulse length (τ)
Peak
Power (P)
2
tc
R
⋅
=
2
τ⋅
=∆
c
R
7. June 17, 2010Digital MultiBeam Radar7
Radar Fundamentals (2)
Frequency modulated continuous wave (FMCW) radar
• Transmit and receive continuously and simultaneously
• No blind zones in range
• Highest possible duty cycle
• Requires separate transmit and receive antennas for highest sensitivity
• Simple transceiver
• Sensitivity is limited by crosstalk between transmit
and receive antennas and the stability of the
transmitted signal
Transmit
antenna
Receive
antenna
Beat signal
Crosstalk
8. June 17, 2010Digital MultiBeam Radar8
Radar Fundamentals (3)
Frequency modulated continuous wave (FMCW) radar
• Linear frequency modulation achieves lowest bandwidth on receive
• Beat frequency
• Example: B = 100 MHz (∆R = 1.5 m), R = 15 km, T = 1 ms → fb = 10 MHz
• factor 10 sampling rate reduction w.r.t.
pulse radar with the same range resolution
Frequency
Time
Beat
frequency (fb)
Sweep
bandwidth (B)
Sweep time (T)
Transmitted
sweep
Echo
cT
RB
T
tB
fb
⋅
⋅
=
⋅
=
2
9. June 17, 2010Digital MultiBeam Radar9
Mid-Air Collision Avoidance
Crowded aerospace leads to accidents
10. June 17, 2010Digital MultiBeam Radar10
Mid-Air Collision Avoidance
Cooperative systems
• Air traffic control (ATC)
• well-established method
• collision avoidance through
transponders and voice
communications with aircraft
• does not work for aircraft
without transponders and/or
comms
• Traffic Collision Avoidance
System (TCAS)
• based on interrogation of
transponders
• independent of ATC
• does not work for aircraft
without transponders
Non-cooperative systems
• Visual flight rules (VFR)
• well-established method
• depends on pilot’s eyes
• does not work in bad weather
• Electro-optical cameras
• relatively mature
• continuous coverage with wide
field-of-view cameras
• no range and range rate information
• does not work in bad weather
• Radar
• all-weather conditions
• range, azimuth, elevation and range
rate measurement
• no continuous coverage (until now)
11. June 17, 2010Digital MultiBeam Radar11
Mid-Air Collision Avoidance
Volume surveillance with radar
10 km
1.5 km
1.5 km
1 km
12. June 17, 2010Digital MultiBeam Radar12
Volume Surveillance with Radar
Pencil beam scanning
• single transmitter and receiver
• long scan time with single pencil beam
(no continuous coverage) Gimbal
Transmitter
Receiver
Transmitter
Receiver
Mechanical scanning
Electronical scanning
Phased array antenna
Reflector antenna
13. June 17, 2010Digital MultiBeam Radar13
Volume Surveillance with Radar
Digital multiple beam radar
• Floodlight transmit beam
• Multiple beams on receive
• Receiver behind each antenna element (continuous coverage)
• Digital beamforming with 2-D FFT
• Doppler filtering with FFT
1-D
FFT
2-D
FFT
Rx
Transmitter
Rx
Rx
Rx
digital
array
antenna
digital
beam
forming
doppler
filter /
ranging
Rx = receiver incl. ADC
14. June 17, 2010Digital MultiBeam Radar14
Airborne Safety Radar
Digital multiple beam radar
• continuous coverage (no scanning beams)
• (frequency modulated) continuous wave (no blind zone)
• planar antenna arrays (easy to integrate in aircraft)
