Figure E-1 --
Vehicle Radar System Diagram
Vehicle radars (also know as automotive radars) are field disturbance sensors that perform some or all of the following;
Forward Crash Avoidance
FORWARD LOOKING RADAR DETECTS MOVING VEHICLES.
- Too Close Warning -- indicates to the driver (with an audio tone, lights, and/or voice alert) the driver is following too close to another vehicle.
- Approaching Too Fast Warning -- indicates to the driver (with an audio tone, lights, and/or voice alert) the driver is approaching another vehicle too fast. System can be designed to brake automatically -- however false alarms could present a problem.
- Adaptive Cruse Control (ACC) -- slows and adjusts vehicle speed automatically when / if the vehicle gets too close to another vehicle; and restores to the preset speed when the other vehicle pulls away.
SIDE RADAR(s) DETECTS STATIONARY OBJECTS AND MOVING VEHICLES.
Detects vehicles / objects in side blind spot(s) and indicates with a light and/or tone. Normal operation might have a green light to indicate blind spot is clear and a red light (audio tone optional) to indicate a vehicle or object detected.
- Opposite-side (opposite driver side) Detection.
- Driver-side Detection.
Rear Blind Spot Detection
REAR RADAR DETECTS STATIONARY OBJECTS.
Detects stationary or slow moving large objects in path of rear of vehicle and warns driver with a tone, light(s), and/or voice alert. Transmits (radiates) only when vehicle in reverse.
- When the vehicle is stopped (speed < 1 kmh or 0.6 mph) transmit power greatly reduced (22 - 25 dB).
Vehicle radars (side blind spot) have been available in some model cars from Toyota since 1989, Nissan since 1993, and Honda since 1994. In the early 90s GM advertised a rear detection vehicle radar. VORAD Safety Systems (Eaton VORAD Technologies) introduced in 1992 a forward and side sensor intended for large vehicle use. In 1999 Mercedes-Benz advertised (for S class cars) an automatic curse control (Distronic forward radar) to track moving vehicles 150 meters (about 500 feet) in front of vehicle. Jaguar, owned by Ford, announced an automatic curse control (forward radar) would be available autumn of 1999 for about 1,400 pounds ($2,249). The Jaguar system sets 45 meters (about 150 feet) as a safe distance between vehicles traveling at 50 mph (80 kmh).
In 1992 Greyhound Bus company started installing blind spot / following too close / approaching too fast indicator systems (VORAD T-200) in 1,500 of its 2,400 vehicle fleet. Accident statistics indicated the systems did not make much, if any, difference and the company started removing the systems in 1995. The system had a number of problems including interference from traffic radars.
The Greyhound bus system used phased-array antennas; a forward looking K band (24.15 GHz for a narrow 3.5 degree beam) and side mounted X band (10.525 GHz with a 140 degree beamwidth) for blind spots. An FM-CW (frequency modulated - continuous wave) waveform allowed the system to derive target range. Transmit power was 0.5 milliwatts, with a nominal detection range of 350 feet. An on-board computer would sense bus steering to establish direction of travel. The computer also incorporated a Fast Fourier Transform (FFT) filter to determine range and closing or opening rate on each detected target.
Forward-looking vehicle radar typical detection range varies from about 300 to 600 feet (about 100 to 200 meters). Radar transmit power (and range) is greatly reduced (-25 dB for forward radar, -22 dB for side and rear radar) when vehicle traveling less than 1 kmh (0.6 mph).
VEHICLE RADAR LIMITS
FCC RULES, PART 15, SECTION 15.253 (1998 Aug 7)
FREQUENCY TOLERANCE BAND
46.8 GHz ± 200 MHz 46.7 - 46.9 GHz
76.5 GHz ± 500 MHz 76.0 - 77.0 GHz
POWER DENSITY at 3 meters (9' 10")
0.2 µW/sq cm speed < 1 kmh
60 µW/sq cm speed >= 1 kmh, Forward Radar
30 µW/sq cm speed >= 1 kmh, Side or Rear Radar
Europe 76-77 GHz
Japan 66 GHz.
Power Density in microwatts per square centimeter (µW/cm2)
Vehicle radars have also been known to operate at traffic radar frequencies in X and K bands, as well as at 35, 60, and 86 GHz. Some systems use ultra wide band (UWB) modulation, an advanced spread spectrum technique. UWB radars must transmit above 24.075 GHz (FCC regulations, Oct 2003).
The Environmental Research Institute of Michigan (ERIM) and TRW have developed (1998) a data base of radar cross-section measurements (radar target size) for situations and at angles pertinent to forward-looking vehicle radar (collision avoidance).