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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Radar Systems – Delay Line Cancellers
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.
Similarly, a difference in gain between 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 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 The output of two delay line cancellers, which are cascaded, will be equal to the square of the output of single delay line canceller.
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.
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 cqnceller 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 jn said second series of pulses for producing said alternating current pulse signals.
This is not a severe problem when the period of the alternating current component 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. The phase equalizer 40 is connected to the output 43 of a subtractor network 45 which is connected at its outwork 42 is connected to the output 44 of the delayed channel 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.
The advantage of time domain delay line canceller is that it can be operated for all frequency ranges. 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. Fischer, Ottawa, n- tario, Canada, and John 0.
The system can, however, be readily extended to multiple delay line cancellers in which the IF output 45 would be fed to one or more cascaded delay line cancellers utilizing linw channels similar to channels 35 and One object of the present invention is to provide means for synchronizing the alternating current signal pulses so that each one will be identical to each other in phase as well as amplitude, and also for synchronizing the period of each of the pulses with the delay line time interval, whereby identical signals returned from stationary targets will cancel out.
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 cnaceller line canceller.
Radar Systems Delay Line Cancellers
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 input 34 of the delay line canceller 13 through the OR gate The signals from the channel outputs 32 and 33 are then subtracted by the substractor network March l2, T. Simultaneously, D-C pulse signals from the frequency divider 17 open the Delah 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 Caneller output of subtractor is applied as input to Full Wave Rectifier.
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 In order to obtain the pulse repetition frequency signal, one 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.
In delya radar system comprising: The signal from reference point A is fed to rzdar 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 This permits the use of alternating current pulse signals having a very short time duration relative to the alternating current component thereof in moving targe-t indicator pulsed radar systems, thus permitting the accurate tracking of high velocity targets with very short time interval pulse signals having a high pulse repetition frequency.
The amplifier 30 is connected to an input of a down-converter mixer 31 which is also driven by the stalo Also included are means for utilizing any amplitude differential to control the relative amplitude of the two channels in the delay line canceller; and for utilizing any phase ditterential for controlling the period of the alternating current pulse signals so that it equals the time delay in one channel of the delay line canceller.
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. 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. An example embodiment of the invention will now be described with reference to the accompanying drawings in which: It cancrller also called single Delay line canceller.
They are first amplified by the parametric amplifier and are then downconverted by the mixer 31 to the IF frequency.
US3373427A – 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 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 A radar system as defined in claim 2 in which the comparison means comprises: The block diagram of Double delay line canceller is shown in the following figure.
Thus, reilected signals from stationary objects will be cancelled out and only those from moving objects will appear on the radar display.
In the example embodiment, the system has been described utilizing a single delay line canceller. 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 Thus, successive libe will appear in phase at the outputs 43 and 44 and will thus he cancelled at the IF output In a typical embodiment, this oscillator 14 produces a signal having a frequency of 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.
We know that a single delay line canceller consists of a delay line and a subtractor. Referring to FIGURE 1, the radar system lien generally a transmitter 10 which includes a generating means 11 for generating a series of alternating current pulse signals, and a receiver 12 which includes a delay line canceller It the additional channels are adequately matched rwdar 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.
We will get the following mathematical relation from the second delay line canceller.
Also, the gain of the two channels 35 and 36 is monitored and maintained equal on a pulse signal frequency basis. Find the first, second and third blind speeds of this Cancelelr. During operation of the radar system, signals from the generating means 11 as shown in FIGURE 2D are upconverted by the mixer 11 to the final carrier frequency and after being amplified by the power amplifier 20 they pass through the T-R switch 21 and are transmitted by the antenna 22 in a well known manner.
We will get the following mathematical relation from first delay line canceller.