Continuous Wave Radar (CW Radar) with block diagram:
The CW radar transmits high frequency signals continuously. The eco signal is received and processed permanently. These radars determine the target velocity rather than its location and they are simple, compact and less costly. CW radar works on the principle of Doppler effect. The Doppler effect is the change in frequency that occurs when a source and target are in relative motion. The CW radar uses the Doppler effect to determine the velocity with which the target is moving. The transmitter produces a continuous sinusoidal signal at a frequency ‘ft’ which is radiated by the antenna on signal by a moving object, the transmitted signal is shifted by Doppler effect by an amount ±fd when the target is moving towards the transmitter or source fd will be positive. If the target is moving away from the source fd will be negative. The detector or mixer multiplies the eco system signal at a frequency, ft ± fd. The Doppler filter allows the difference frequency component to pass through and rejects the higher frequency. The output of the detector is amplified by a power amplifier.
Frequency Modulated Continuous Wave Radar
The frequency modulated continuous wave radar (FMCW) is capable of measuring the relative velocity and range of the target depending on the band width of the signal. The time taken by the transmitted signal to reach the receiver and return back to the transmitter is calculated. In the transmitting section, the transmitted signal is frequency modulated by using a FM modulator. The modulated signal is propagated on to the receiver. In the receiving section, the frequency modulated signal is mixed with a high Band Width signal inside a mixer. The output of the mixer is a signal having large Band Width. This signal is amplified and applied to a limiter circuit. The limiter circuit removes the unwanted frequency components. This signal is demodulated and applied to an indicator which provides the location of the target. The location of the target is deciseded by comparing the signal value with a predefined threshold value. If the value of the signal is greater than the threshold value, it is decised that a target is present at a certain distance. If the value of the signal is less than the threshold value, it is deciseded that noise is present.