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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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 The amplifier 30 is connected to an input of a down-converter mixer 31 which is also driven by the stalo This fact is used to eliminate reilections from stationary objects so that only those from moving targets will be shown on the radar display.
US3373427A – Delay line canceller for radar system – Google Patents
March l2, T. 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 FIGURE 1 is a block schematic diagram of part of a radar system utilizing a delay line canceller of dealy present invention; and.
Received signals from either stationary or moving objects, are fed from the antenna 22 through the T-R switch 21 to the receiver In the past, one of the problems encountered in such a moving target indicator radad, is that the initial phase of the alternating current component varies from one transmitted pulse to the next. The signals from the channel outputs 32 cancceller 33 are then subtracted by the substractor network 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.
The frequency response characteristics of both double delay line canceller and the cascaded combination of two delay line cancellers are the same. An example embodiment of the invention will now be described with reference to the accompanying drawings in which:.
We will get the following mathematical relation from first delay line canceller. 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 the frequency of the voltage controlled crystal oscillator Simultaneously, D-C pulse signals from the frequency divider 17 open the AND gate 50 so as lune couple any residual signals from the output of the subtractor network 45 to inputs of the amplitude demodulator 51 and the phase demodulator The output of the mixer 31 is coupled through an IF amplifier 32 to one input of an OR gate 33 which, in turn, is connected to the input 34 of the delay line canceller 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 If any of these conditions do not exist, a residual output from the subtractor network will be obtained.
The output of subtractor is applied as input to Full Wave Rectifier. However, when very short pulse intervals are transmitted having only a few cycles of alternating current componenta difference delsy 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.
Hence, complete cancellation of the two signals will not take place and an output from the IF output 46 will be obtained. Thus, successive pulses will appear in phase at the outputs 43 and 44 and will thus he cancelled at selay IF output In the lime embodiment, the system has been described utilizing a single delay line canceller. The advantage of time domain delay line canceller is that it can be operated for all frequency ranges. 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.
Radar Systems Delay Line Cancellers
It is nothing cancelled the frequency response of the single delay line canceller. 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. The input 34 of the delay line canceller 13 is connected to two channels; 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 output from the mixer 18 is coupled to a power amplier 20, which in turn is connected through a transmit-receive or T-R switch 21 to an antenna It the additional channels are cancellet 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 cnaceller the chain.
The advantage of double delay line canceller is that it rejects the clutter broadly.
USA – Delay line canceller for radar system – Google Patents
Eadar 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. This means, it allows the AC components of echo signals received from non-stationary targets, i.
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 dleay 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 ij 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.
Fischer, Ottawa, n- tario, Canada, and John 0.
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 Since the stalo 19 is common to both the upconverter mixer 1S and the downconvertcr mixer 31, IF signals reflected from stationary objects which do not undergo any Doppler shift will be identical in frequency to those at the output of the carrier gate 15 as shown in FIGURE 2D.
We will get the following mathematical relation from the second delay line canceller. 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 two channels similar to channels 35 and 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.
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 delau amplified by the power amplifier 20 they pass through rsdar T-R switch 21 and are transmitted by the antenna 22 in a well known manner.
In a typical embodiment, this oscillator 14 produces a signal having a frequency of An example lind of the invention will now be described with reference to the accompanying drawings in which: 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 celay residual signal will result.
In a radar system comprising: As the name suggests, delay line introduces a certain amount of delay. This is not a severe problem when the period of the alternating current component is relatively short compared to that of the pulse width, on the residual phase error will only account for a small portion of the total signal width.
We know that a single delay line canceller consists of a delay line and a subtractor.
In a radar system, any received signal reilected from a stationary object will be exactly similar, in magnitude and phase, to the im one, being displaced from it in time by the period of successive transmitter pulses.