1-18
Doppler Shift for Target Moving Toward Fixed Radar (Hz)
5
0
10
15
20
25
30
40
10
100
1K
10K
100K
1M
Text Box: Radar Frequency (GHz)
Radar Frequency (GHz)
Text Box: 4km/h - Man or Slow Moving Vechile
4km/h - Man or Slow Moving Vechile
Text Box: 100km/h - Vehicle, Ground or Air
100km/h - Vehicle, Ground or Air
Text Box: 700km/h - Subsonic Aircraft
700km/h - Subsonic Aircraft
Text Box: 2,400 km/h - Mach 2 Aircraft
2,400 km/h - Mach 2 Aircraft
X-Band RADAR
     
Doppler Shifts
   Doppler radars require low-phase-noise oscillators.  The velocity of the target and the radar frequency are the primary factors that determine the oscillator noise requirements. For example, to detect slow-moving targets, the noise close to the carrier must be low.
   The Doppler shift* of an object moving towards the observer is given by f/f = 2v/c, where f is the Doppler frequency shift, v is the velocity of the object, and c is the speed of light.


* Doppler shift example:  if v = 4 km/h and f = 10 GHz (e.g., a slow-moving vehicle approaching an X-band radar), then f = 74 Hz, i.e., an oscillator with low phase noise at 74Hz from the carrier is necessary in order for a coherent radar system to "see" the vehicle.