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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It is nothing but the frequency response of the single delay line canceller.
Hence, complete cancellation of the two signals will not take place and an output from the IF output 46 will be obtained. 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 It the additional channels are adequately matched in performance to those of the delay line canceller 13, the single amplitude error signal derived from the amplifier 52 can be used to control the gains of all the channels in the chain.
Find the first, second and third blind speeds of this Radar. 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. The generating means 11 inculdes a voltage controlled crystal oscillator 14 which is connected to one input of a carrier gate 15 and also to a pulse generator Delay line cancellers can be classified into the following two types based on the number of delay lines that are present in it.
A radar system as defined in claim 2 in which the comparison means comprises: Complete cancellaion will only occur when the period of the signal from the carrier gate 15 is equal to the time delay of the delay line 41, the initial phase of the alternating current component of each pulse signal at D is a constant, the received IF signals reflected from targets are identical in frequency to those at the output of the carrier gate 15, and the gains of the two channels 35 and 36 are equal.
So, the relative velocities for which the frequency response of the single delay line canceller becomes zero are called blind speeds.
The block diagram of MTI receiver with single Delay line canceller is shown in the figure below. When a Doppler phase shift is encountered due to refiection from a moving object, the time delay between the reception of successive pulse signals will not equal that of the delay line 41, and the IF signals reflected from the moving object will not be identical in frequency to those at the output of the carrier gate The I-F signals from the amplifier 32 are coupled 4 through the OR gate 33 to the input 34 of the delay line canceller 13 where they are split, one half passing through the undelayed channel 35 and the other through the delayed channel This invention relates to a moving target indicator system utilizing a radio frequency delay line canceller and more particularly to a means for synchronizing the period of the transmitted alternating current pulse signals with the time delay encountered in the delay line canceller.
US3373427A – Delay line canceller for radar system – Google Patents
A phase error signal will then be coupled from the phase relay 53 and after passing through the integrating amplifier 55 will be used to control the frequency of the voltage controlled crystal oscillator The output of two delay line cancellers, which are cascaded, will be equal to the square of the output of single delay line canceller.
In a typical embodiment, this oscillator 14 produces a signal having a frequency of 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 March l2, T.
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.
The amplifier 30 is connected to an input of a down-converter mixer lihe which is also driven by the stalo An example embodiment of the invention will now be described with reference to the accompanying drawings in which:. The advantage of double delay line canceller is that it rejects the clutter acnceller.
The delay line canceller 13 also includes an AND gate 50 havingone input connected to the IF racar 46 and the other input connected to the output of the frequency divider It also improves the stationary target cancelleer capabilities of moving target indicator pulsed radar systems utilizing intermediate frequency delay line cancellers and longer pulse widths.
The phase demodulator 53 is, in turn, connected through an integrating amplifier 55, the acnceller of which is used to control the frequency of the voltage controlled crystal oscillator In this manner the period of lthe alternating current pulse signal from the generating means 11 is made to the time delay interval between the two channels 35 and They are first amplified by the parametric amplifier and are then downconverted by the mixer 31 to the IF frequency.
The signals from the channel outputs 32 and 33 are then subtracted by the substractor network To insure this, the present invention provides that during the transmission interval, alternating current pulse signals from the carrier gate 15 are coupled to the cancellr 34 of the delay line canceller 13 through the OR gate 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 output of subtractor is applied as input to Full Wave Rectifier. 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.
Radar Systems Delay Line Cancellers
The improvement comprises means for connecting a sample of the alternating current pulse signal generated by the transmitter in the radar system to the input of the delay line canceller; rafar for comparing the amplitude and phase of the alternating current component of this signal at the subt-racted output of the canceller against the alternating current component of the canceloer pulse signal samples.
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.
Signal processor for reducing clutter and eliminating range ambiguities in target detection systems. In one embodiment of such a system, cancellef invention includes means for controlling the frequency of the alternating current component of the alternating current pulse signals so that it is an integral multiple of the reciprocal of the delay line period.
Thus, successive pulses will appear in phase at the outputs 43 and 44 and will thus he cancelled at the IF output Any residual output from the subtractor network 45 which is in phase with that of the voltage controlled crystal oscillator 14, results in an arnplitude error signal which is coupled through the integrating ampliier 52 and is used to control the variable gain network 42 until the gain of the two channels 35 and 36 is equal.
The signal from reference point A is fed to the carrier gate which is gated by the signal from reference point C so as to produce at its output, reference point D, a series of alternating current pulse signals having an A-C component of 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