What is blind speed in radar ?

Doppler shift is a change in the frequency of a wave, such as a radar signal, due to the motion of the target reflecting the signal. In radar systems, the Doppler effect is used to measure the speed of objects, such as aircraft or vehicles, by analyzing the frequency shift between the transmitted and received radar signals. The blind speed refers to situation where doppler shift of radar signal is unable to accurately detect the speed or velocity of a target.

Blind speed occurs when doppler shift is equal to or very close to zero, making it difficult for radar system to determine the target's speed accurately. This happens when target is moving directly toward or away from the radar antenna, causing minimal frequency shift in the reflected signal. In such cases, the radar may not be able to distinguish between stationary objects and those moving at blind speed.

To overcome this blind speed problem, radar systems often employ various techniques, such as multiple radar antennas with different orientations, PRF (Pulse Repetition Frequency) modulation or signal processing techniques. These techniques help radar to detect and measure speeds of targets even when they are moving at or near blind speeds.

Radar Blind Speed formula

➨One of the formula to calculate blind speed in radar is as follows.
Vblind = { c / ( 2 * f * cos(θ)) }
Where,
Vblind is blind speed in meters per second
c is the speed of light, 3 x 108 m/s
f is the operating frequency in Hz
θ is the angle between radar beam and direction of motion of the target (measured in radians) .

➨The another radar blind speed formula is as follows. This formula is used in the Radar Blind Speed calculator mentioned below.

Blind Speed Equation

Radar Blind Speed Calculator

Frequency of operation (GHz) input1 :

Pulse Repetition Time (µsec) input2 :


Aircraft Blind Speed output :

Example of Blind speed calculation :
INPUTS: Frequency (MHz) = 2.5 GHz, PRT = 20 µs,
OUTPUT: Blind Speed (m/s) = 3000

Conclusion : The blind speed in radar can be calculated using formulas based on radar frequency, wavelength and pulse repetition time (PRT). It is critical consideration in radar systems for accurate target velocity measurements.


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