RADAR and Doppler RADAR

RADAR Definition

RAdio Detection And Ranging

RADAR Applications

• Target detection and tracking

• Speed detection – Doppler Radar

• Weather radar

• Imaging radar

• Medical imaging

• Car radar

Types of RADAR

• Mono-Static: one antenna for transmitting and receiving

• Bi-Static: one antenna for transmitting and one antenna for receiving

• Multi-Static: multiple antennas for transmitting and receiving

• Passive: FM transmitter, reference antenna and target antenna

RADAR equation

Continuous Wave (CW) Doppler RADAR

• Simplest type of RADAR

• Used to measure speed of target but provides NO range information

• Police speed traps

• Motion detection

Doppler RADAR equation

• Transmit frequency is f₀

• Received frequency is f_r = f₀ + f_D

• Doppler frequency is f_D = 2v/c * f₀

• If target is moving away from radar then the doppler frequency is subtracted

Doppler relative velocity

In a Doppler radar system, it is the relative velocity between the radar and the target that gives the Doppler shift

• If f_D = 0, both cars are at the same speed (relative velocity = 0)

• If f_D < 0, then v1 > v2

• If f_D > 0, then v1 < v2

Simple CW Doppler RADAR

• Tx signal = A cos𝜔𝑡𝑡

• Rx signal = B cos𝜔𝑟𝑡 ← Doppler shifter signal

• At a mixer Rx is multiplied by a portion of Tx signal (C cos𝜔𝑡𝑡)

• So output from mixer is S = BC cos𝜔𝑟𝑡 cos𝜔𝑡𝑡

• Expanding and applying low pass filter gives doppler frequency: 𝐵𝐶/2 [cos(𝜔𝑟 − 𝜔𝑡) 𝑡]