MTI (Moving Target Indication) radar systems have been built for many years, based on . The simple MTI delay-line canceller shown in Fig.4 is an example of a. Download scientific diagram | Block Diagram for Double Delay Line Canceller from publication: Implementation of MTI based Pulse compression Radar system . The MTI radar uses Low Pulse Repetition Frequency (PRF) to avoid range ambiguities. . Y. &. D. E. S. I. G. N. I. I. S. T. Effect of delay line canceller on the signal.
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Find the first, second and third blind speeds of this Radar.
US3373427A – Delay line canceller for radar system – Google Patents
Also, the gain of the two channels 35 and 36 is monitored and maintained equal on a pulse signal frequency basis. This is not a severe problem when the period of the alternating current cancellsr is relatively short compared to that of the pulse width, since the residual phase error will only account for a small portion of the total signal width.
If the time delay in the delayed channel 36 relative to that in the undelayed channel 3S is not equal to the period of the alternating current pulse signal from the generating means 11, successive signals will not completely cancel at the output of the subtractor network Delay line canceller is a filter, which eliminates the DC ln of echo signals received from stationary targets. The input 34 of fanceller delay line canceller 13 is connected to two dwlay an undelayed channel 35 which includes a phase equalizer 40, and a delayed channel 36 which includes a delay line 41 and a variable gain network The advantage of time domain delay line canceller is that it can be operated for all frequency ranges.
Radar Systems Delay Line Cancellers
Homodyne FMCW radar range resolution effects with sinusoidal nonlinearities in the frequency sweep. An example embodiment of the invention will now be described with reference to the accompanying drawings in which: Input to the antenna 22 is coupled back through the T-R switch 21 to the input of the receiver 12 where it is coupled through a parametric amplifier On the other hand, a reflected signal from a moving object will differ from its predecessor at least in phase because the object will move through a distance between successive pulses which is not negligible compared with the transmitter wavelength.
This fact is used to eliminate reilections from stationary objects so that only those from moving targets will be shown on the radar display. In the example embodiment, the system has been described utilizing a single delay line dellay.
The signals from the channel outputs 32 and 33 are then subtracted by the substractor network The outputs 43 and 44 are connected to the input of a subtractor network 45 which is connected at its output to the IF output However, when very short pulse intervals are transmitted having only a few cycles of alternating current componenta difference in phase between the alternating current components of the two signals would result in substantial residual signals which appear as moving targets on the 4radar display.
Theuinvention is particularly useful in radar systems where the pulse width approaches the period of the radio frequency signal. Simultaneously, D-C pulse signals from the frequency divider 17 open the AND gate 50 so as to couple any residual signals from the output of the subtractor network 45 to inputs of the amplitude demodulator 51 and the phase demodulator In a typical embodiment, this oscillator 14 produces a signal having a frequency of Still another problem is that if the period of the transmitted pulse signals does not equal the time delay in the delay line canceller, the delayed and undelayed signals reflected from stationary objects will not arrive in time coincidence at the output of the canceller, and a residual signal will result.
Therefore, the output of Full Wave Rectifier looks like as shown in the following figure. In the past, one of the problems encountered in such a moving target indicator system, is that the initial phase of the alternating current component varies from one transmitted pulse to the next. The frequency response characteristics of both double delay line canceller and the cascaded combination of two delay line cancellers are the same. These pulses are then frequency divided by the frequency divider 17 by a ratio of to produce at its output, reference point C, a series of nanosecond D-C gating pulses having a pulse repetition rate of 6.
Radar Systems – Delay Line Cancellers
In addition, since the carrier gate 15 is triggered by the output of a frequency divider 17 which in turn is controlled by the voltage controlled crystal oscillator 14, the. The combination of a delay line and a subtractor is known as Delay line canceller. Thus, reilected signals from stationary objects will be cancelled out and only those from moving objects will appear on the radar display.
The output of the carrier gate 15 is connected to an input of an upconverter mixer 1’8 which is driven by a stable local oscillator or stalo Hence, complete cancellation of the two signals will not take place and an output from the IF output 46 will be obtained. Another object of the invention is to provide a means for dynamically controlling the relative gain of the delayed and undelayed channels in the delay line canceller so that consecutive pulse signals returned from stationary targets will be substantially cancelled out.
Hence, when one pulse is subtracted raear another in the delay line canceller, a residual signal is lett which appears on the radar display. So, the delay line is mainly used in Delay line canceller in order to introduce a delay of pulse repetition time. A phase error signal will then be coupled from the phase demodulator 53 and after passing through the integrating amplifier 55 will be used to control rqdar frequency of the voltage controlled crystal oscillator Signal processor for reducing clutter and eliminating range ambiguities in target detection systems.
They are first amplified by the depay amplifier and are then downconverted by the mixer 31 to the IF frequency. When the signals are reflected from stationary objects, the time delay in the channel 36 which includes the delay line 41 is equal to the period between successive transmitted pulses.
Kennedy and Edgar J. This in turn alters the repetition frequency of the D-C pulses from the frequency divider 17 until the period thereof is equal to the time interval of the delay line The output of the AND gate 50 is connected to one cancellet of an amplitude demodulator 51 which utilizes as its reference signal the output of the voltage controlled crystal oscillator In addition, since the carrier gate 15 is triggered by the output of a frequency divider 17 which in turn is controlled by the voltage controlled crystal oscillator 14, the phase of the alternating current component of each pulse signal, illustrated in FIGURE 2D, will be constant.
The phase equalizer 40 is connected to the output 43 of a subtractor network acnceller which is connected at its outwork 42 is connected delqy the output iin of the delayed channel This invention furthermore permits conversion of more conventional moving target indicator pulsed radar systems utilizing video delay line cancellers to superior performance systems utilizing intermediate frequency delay line cancellers.
USA – Delay line canceller for radar system – Google Patents
The phase demodulator 53 is, in turn, connected through an integrating amplifier 55, the output of which is used oine control the frequency of the voltage controlled crystal oscillator Referring to FIGURE 1, the radar system comprises generally a transmitter 10 which includes a generating means 11 for generating a series of alternating current pulse signals, and a deoay 12 which includes a delay line canceller We will get the following mathematical relation from first delay line canceller.
In order to obtain the pulse repetition frequency signal, canceler output from the voltage controlled crystal oscillator 14 is fed to the pulse generator 16 which produces at its output, reference point B, a series of l nanosecond pulses as shown in FIGURE 2B.
Fischer, Ottawa, n- tario, Canada, and John 0.