Frequency-Modulated Continuous-Wave (FMCW) Radar
Frequency-Modulated Continuous-Wave (FMCW) Radar
Ordinary pulsed radar detects the range to a target by emitting a short pulse and observing the time of flight of the target echo. This requires the radar to have high instantaneous transmit power and often results in a radar with a large, expensive physical apparatus. Frequency-modulated continuous-wave (FMCW) radars achieve similar results using much smaller instantaneous transmit powers and physical size by continuously emitting periodic pulses whose frequency content varies with time. A very important type of FMCW radar pulse is the linear FM sweep. In this case, the range to the target is found by detecting the frequency difference between the received and emitted radar signals. The range to the target is proportional to this frequency difference, which is also referred to as the beat frequency.
This Demonstration investigates the performance of a W-band (94 GHz) FMCW radar emitting an FM sweep with a 5 kHz pulse repetition frequency. You can select the range to the target , the target radar cross section , the transmit power of the radar , and the gain of the radar transmit-receive antenna. These four parameters, together with the radar wavelength (= 3.2 mm at 94 GHz), control the target echo power.
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Like all types of radar, FMCW radar is limited by the effects of thermal noise in the radar electronic circuits. The radar noise factor NF controls the radar thermal noise floor relative to the theoretical lower limit set by black body radiation. Additionally, FMCW radars are limited by the effects of unwanted phase noise that propagates via parasitic paths within the radar electronics. Phase noise effects on radar performance in the Demonstration are controlled by the losses and on the two parasitic paths and the travel times and on these paths measured relative to the travel time of the reference signal from the signal generator to the radar mixer. The radar sweep width controls radar range resolution. Large sweep widths improve range resolution and increase the target beat frequency. This enables target detection at higher frequencies where phase noise is lower.
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