According to the figure, the microscopic portion of the transmitter output power is mixed with the output of a local oscillator and this mixture is fed into the receiver mixer. The receiver mixer also receives the Doppler shift signal from the antenna and produces an output differential frequency (30 MHz + Doppler frequency). The output of this mixer is amplified and re-modulated, and the signal of the second detector is in the Doppler frequency because its sign is terminated so that it tells. It is not possible that the target is approaching or moving away. The receiver system is generally similar to a super heterodyne in that additional sensitivity is achieved by lowering the noise as the output of the diode mixer is now near 30 MHz at which the FM noise terminates. In this, separate antennas are shown for transmitter and receiving but this is not necessary. A circulator can be used to use the same antenna. Using separate antenna can ensure complete isolation of transmitter and receiver.
Thus the receiver can be shielded from the humming of the transmitter. This type of radar has a CW power of 100 W or less. Gun or IMPATT diode CW magnetrons are used for high power transmitters. These operate in the frequency range of pulse radar.
Advantages
Following are the benefits of CW Doppler radar
- It can accurately calculate relative velocity
- It reduces power loss
- Their circuits are relatively simple and the size of the equipment used is small.
- There is no effect in the presence of permanent targets.
- It can also operate up to zero range because the receiver is on all the time
- Through this, the speed of high range targets can be measured quickly and accurately.
- By applying some additional circuits, it can measure the target's velocity along with its direction.
Following are the applications of CW Doppler radar -
- Used for speed measurement in aircraft navigation
- Used in the rate off - climb scale
- Used in radar speed motors used by police
CW Doppler radar has the following limitations
- Its range is also limited due to its transmit power being limited.
- Being in the target space reduces the clarity in its display, filters are used along with the circuit to remove it.
- Doppler radar is unable to index the range of the target, it can only tell the target speed
- In this, the transmint signal is amodulated, due to which it is not able to detect the timing of the receiving signal.
0 تعليقات
Please give your suggestions in comments.