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{\displaystyle AZ} <> As the name suggests, delay line introduces a certain amount of delay. The two methods described earlier are not the only ones that are used for obtaining coherent reference signals in the MTI. 317 0 obj <> endobj 0000011762 00000 n The phase of each transmit pulse is different from the previous and future transmit pulses. 0000060858 00000 n endstream endobj 326 0 obj <> endobj 327 0 obj <> endobj 328 0 obj <>stream 0000005757 00000 n

According to Doppler effect, the frequency of the received signal will increase if the target is moving towards the direction of Radar. This may lead to wrong detection of moving target although only clutter is present. <>/ProcSet[/PDF/Text]/ColorSpace<>/Font<>>>/B[39 0 R 40 0 R]/MediaBox[0 0 595 842]/Annots[41 0 R 42 0 R 43 0 R]/Rotate 0>> Usually, doppler radar refers to CW signals like police speed radars. Radio waves travel at the speed of light, so the distance to the object is the elapsed time multiplied by the speed of light, divided by two - there and back. Chapter 3- pulsed radar system and MTI 1. endobj L Coherent detection requires dealing with the envelope of a signal, g (t) and the phase of the sinusoidal carrier, Φ (t). '$�?&��9\: ��>�d��T*�L$��X,�D��= Pulsed radar system The time-delay between the transmission of each pulse and the reception of the echo of the same pulse is proportional to the target range. From Equation 3, we can observe that the frequency response of the single delay line canceller becomes zero, when $\pi f_dT_P$ is equal to integer multiples of $\pi$ This means, $\pi f_dT_P$ is equal to $n\pi$ Mathematically, it can be written as, $$\Rightarrow f_d=\frac{n}{T_P}\:\:\:\:\:Equation\:4$$. Solution This allows moving objects about 300 times smaller to be detected in close proximity to larger stationary objects. The coherent MTI radar differentiates moving targets from stationary targets by using the Doppler shift passed on to the reflected signal by a moving target. Now, let us discuss about these two MTI Radars one by one. In addition to that, it also eliminates the AC components of echo signals received from non-stationary targets, when the Doppler frequency $f_d$ is equal to integer (other than zero) multiples of pulse repetition frequency $f_P$. $$r\left ( t \right )=p\left ( t \right )-p\left ( t-T_P \right )-\left [ p\left ( t-T_P \right )-p\left ( t-2T_P \right ) \right ]$$, $$\Rightarrow r\left ( t \right )=p\left ( t \right )-2p\left ( t-T_P \right )+p\left ( t-2T_P \right )\:\:\:\:\:Equation\:12$$. pulse doppler radar , in this the radar send the pulse train to detect the position of target and MTI(moving target indicator) in which it detect the target which is moving but pulse radar can detect the moving target but there is a disadvantage that the problem of blind speed arises and pulse radar dosn't continuosly transmit the 0000007930 00000 n The target location accuracy is proportional to the slant range, frequency and aperture length. 360 Modern radars generally perform all of these MTI techniques as part of a wider suite of signal processing being carried out by digital signal processors. Stationary objects did not change the phase from pulse to pulse, but moving objects did. The blocks corresponding to the receiver section will be same in both the block diagrams.

A fast revisit rate becomes critical to providing an uncorrupted track when a target moves in dense traffic or is temporarily obscured, if only by trees along a road. They need not be measured directly, but can be derived using inphase (I ) and quadrature (Q) channels. Coherent Oscillator − It produces a signal having an Intermediate Frequency, $f_c$. $$\Rightarrow f_d=nf_P\:\:\:\:\:Equation\:6$$. $$q\left ( t \right )=p\left ( t \right )-p\left ( t-T_P \right )\:\:\:\:\:Equation\:9$$. So, the magnitude of output of double delay line canceller, which is present at MTI Radar receiver will be equal to $4A^2\left ( \sin\left [ \pi f_dT_P \right ] \right )^2$. 0000005281 00000 n Hence, it is also called stable Local Oscillator.