Radio detection and ranging (radar
) is used to sense angle, range and velocity of (moving) scatterers in the environment . Radar sensor
figures of merit include maximum range and solid angle
, as well as angular, range and velocity resolution. Range and velocity are detected through pulse delay ranging and the Doppler effect
), or through the frequency modulated continuous wave (FMCW
) technique and range differentiation. Angle is detected by scanning the volume with a highly directive beam. Scanning is done mechanically, by rotating an antenna, or electronically, by steering the beam of an array. Angular resolution depends on the beamwidth of the antenna or the array, but techniques such as monopulse
significantly increase the angular accuracy of pulse-Doppler radars beyond real beamwidth. The range resolution is limited by the instantaneous signal bandwidth of the radar sensor in both pulse-Doppler and FMCW radars. Monopulse-Doppler radars, which offer advantages over FMCW radars, such as:
- Half-duplex operation: Pulsed radars are half-duplex. Hence, they provide higher isolation between transmitter and receiver, increasing the receiver's dynamic range (DR) and the range detection considerably. In addition, an antenna or an array can be time-shared between transmitter and receiver whereas FMCW radars require two antennas or arrays, one for transmit and one for receive.
- Monopulse: The monopulse technique increases the angular accuracy to a fraction of the beamwidth by comparing echoes, which originate from a single radiated pulse and which are received in two or more concurrent and spatially-orthogonal beams.
- Pulse-Doppler processing: Pulse-Doppler processing transforms echoes originating from a radiated burst to the spectral domain using a discrete fourier transform (DFT). In the spectral domain, stationary clutter can be removed because it has a Doppler frequency shift which is different from the Doppler frequency shift of a moving target. Range and velocity can be estimated with increased signal to noise ratio (SNR) due to coherent integration of echoes.