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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US3373427A – Delay line canceller for radar system – Google Patents
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. Rdar 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 raear Received signals from either stationary or moving objects, are fed from the antenna 22 through the T-R switch 21 to cancepler receiver The delay line canceller 13 also includes an AND gate 50 havingone input delya to the IF output 46 and the other input connected to the output of the frequency divider It also improves the stationary target cancellation capabilities of moving target indicator pulsed radar systems utilizing intermediate frequency delay line cancellers and longer pulse widths.
This produces a control signal at the cancellers output which is used to control the periodI of the transmitted pulse signals so that the period is lije synchronized with the time delay encountered in the canceller. One way of accomplishing this is to delay the reflected signal due to one transmitter pulse by a time interval equal to the period of the pulses and then subtract it from the reflected signal due to the succeeding pulse.
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.
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. Thus, successive pulses will appear in phase at the outputs 43 and 44 and will thus he cancelled at the IF output Fischer, Ottawa, n- tario, Canada, and John 0.
In one embodiment of such a system, the 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.
This not only insures that the pulse signal frequency is linked to the delay line period, but that the initial phase of the alternating current component of each transmitter pulse signal is constant. The other input to the OR gate 33 is derived from the output of the carrier gate What is claimed is: Input to the antenna 22 is coupled back through the T-R switch 21 to the input of the radra 12 where it is coupled through a parametric amplifier Similarly, a difference in gain canveller the two channels 35 and 36 results in an output signal from the subtractor network 45 which is coupled through the AND gate 5 to the amplitude demodulator 51 where it is referenced against a signal from the voltage controlled crystal oscillator Thus, reilected signals from stationary objects will be cancelled out and only those from moving objects will appear on the radar display.
This fact is used to eliminate reilections from stationary objects so that only those from moving targets will be shown 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. 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.
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.
The output of two delay line cancellers, which are cascaded, will be equal to the square of the output of single delay line canceller.
USA – Delay line canceller for radar system – Google Patents
So, the relative velocities for which the frequency response of the single delay line canceller becomes zero are called blind speeds. 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 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 A radar system as deiined in claim 1 in which the generating means comprises a voltage controlled oscillator for generating an alternating current signal, the frequency of which is controlled by said phase error signal; a pulse generator responsive to said alternating current signal for producing a rst series of pulses; a frequency divider responsive to said tirst series of pulses for producing a second series of pulses subharmonically related to said rst series of pulses, each of said second ser-ies of pulses having a predetermined width; gate means responsive to said alternating current signal and said second series of pulses for producing said alternating current pulse signals.
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 The pulse generator 16 is, in turn, connected to a frequency divider 17, the output of which is connected to the other input of the carrier gate It is nothing but the frequency response of the single delay line canceller.
We will get the following mathematical relation from the second delay line canceller.
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. When jn 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.
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 delzy 35 and the other through the delayed channel Find the first, second and third blind speeds of this Radar.
Therefore, the output delayy Full Wave Rectifier looks like as shown in the following figure.