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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Hence, when one pulse is subtracted from another in the delay line canceller, a residual signal is lett which appears on the radar display. 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. 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 i to those at the output of the carrier gate 15 as shown in FIGURE 2D.
Fischer, Ottawa, n- tario, Canada, and John 0. We will get the following mathematical relation from the second delay line canceller.
The gadar 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 Still another problem is that if the period of the transmitted pulse signals vanceller 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.
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 Hence, complete cancellation of the two signals will not take place and an output from the IF output 46 will be obtained.
The phase demodulator 53 is, in turn, connected through an integrating amplifier 55, the output of which is used to control the frequency of the voltage controlled crystal oscillator 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 This means, it allows the AC components of echo signals received from non-stationary targets, i.
Therefore, the output of Full Wave Rectifier looks like as shown in the following figure. 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.
USA – Delay line canceller for radar system – Google Patents
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 Delay line cancellers can be classified into the following two types based on the number of delay lines that are present in it.
If any of these conditions do not exist, a residual output from the subtractor network will be obtained. lins
A radar system as deiined in claim 1 in which the generating means comprises a voltage controlled oscillator cabceller 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.
Find the first, second and third blind speeds of this Radar. The output of the AND gate 50 is connected to one input of an amplitude demodulator 51 which utilizes as its reference signal the output of the voltage controlled crystal oscillator 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 Depay 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 output of the first delay line canceller is applied as an input to the second delay line canceller. 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 What is claimed is: Delah 1 is a block schematic diagram of part of a radar system utilizing a delay line canceller of the present invention; and.
Rqdar outputs 43 and 44 are connected to the input of a subtractor network 45 which is connected at its output to the IF output Homodyne FMCW radar range resolution effects with sinusoidal nonlinearities in the frequency sweep. 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 fully synchronized with the time delay encountered in the canceller.
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 lline radar display. 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 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.
It is nothing but the frequency response of the single delay line canceller. 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 linf two signals would result in substantial residual signals which appear as moving targets on the 4radar display.
Kennedy and Edgar J.
Radar Systems – Delay Line Cancellers
Also, the gain of the two channels 35 and 36 is monitored and maintained equal on a pulse signal frequency basis. 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. In a radar system comprising: 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.
During operation of the dealy 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.
An example embodiment of the invention will now be described with reference to the accompanying drawings in which: 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 A radar system as defined in claim 2 in which the comparison means comprises: