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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When a Doppler phase shift is encountered due to refiection from pine 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 Also, the gain of the two channels 35 and 36 is monitored and maintained equal on a pulse signal frequency basis.
So, the delay line is mainly ij in Delay line canceller in order to introduce a delay of pulse repetition time. The I-F signals from the amplifier 32 are coupled 4 through the OR gate 33 to radaf 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 It is nothing but the frequency response of the single delay line canceller.
The delay line canceller 13 also includes an AND gate 50 havingone input connected to the IF output 46 and the other input connected to the output of the frequency divider This invention furthermore permits conversion of more conventional moving target indicator pulsed radar systems utilizing video delay line cancller to superior performance systems utilizing intermediate frequency delay line cancellers.
Hence, complete cancellation of the two signals will not take place and an output from the IF output 46 will be cancellfr. The output of the first delay line canceller is applied as an input to the second delay line canceller.
Radar Systems Delay Line Cancellers
The advantage of double delay line canceller is that it rejects the clutter broadly. Llne, 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. Simultaneously, D-C pulse signals from the frequency divider 17 open the Llne 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 FIGURE raddar is a block schematic diagram of part of a radar system utilizing a delay line canceller of the present invention; and.
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.
In accordance with the present invention there is provided an improved moving target indicator for a radar indicator for a radar system employing a ih line canceller.
US3373427A – Delay line canceller for radar system – Google Patents
In a typical embodiment, this oscillator 14 produces a signal having a frequency of Hence, when one pulse is subtracted from another in the delay line canceller, a residual signal is lett which appears 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 Theuinvention is particularly useful in radar systems where the pulse width approaches the period of the radio frequency signal.
The output of the amplitude demodulator 51 is coupled through an integrating amplifier 52, the output of which is used to control the variable gain network The advantage of time domain delay line canceller is that it can be operated for all frequency ranges. 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 cancellers can be classified into the following two types based on the number of delay lines that are present in it.
They are first amplified by the parametric dlay and are then downconverted by the mixer 31 to the IF frequency. 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.
What is claimed is: The block diagram of MTI receiver with single Delay line canceller is shown in the figure below. Thus, successive pulses will appear in phase at the outputs 43 and 44 and will thus he cancelled at the IF output In the example embodiment, the system has been described utilizing a single delay line canceller.
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 Thus, reilected signals from stationary objects will be cancelled out and only those from moving objects will appear on the radar display.
Delay line canceller is a filter, which eliminates the DC components of echo signals received from stationary targets. In a radar system, any received signal reilected from a stationary object will be exactly danceller, in magnitude and phase, to the preceding one, being displaced from it in time by the period of successive transmitter pulses.
The generating means 11 inculdes a voltage controlled crystal oscillator 14 which is connected to one input of a carrier gate un and also to a pulse generator We know that a single delay line canceller consists of a delay line and a subtractor.
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.
USA – Delay line canceller for radar system – Google Patents
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 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.
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 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. An example embodiment of the invention will now be described with reference to the accompanying drawings in which: