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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If any of these conditions do not exist, a residual output from the subtractor network will be obtained. In this manner the period of lthe radzr current pulse signal from the generating means 11 is velay to the time delay interval between the two channels 35 and Kennedy and Edgar J.
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. It also improves the stationary target cancellation capabilities of moving target indicator dleay radar systems utilizing intermediate raar delay line cancellers and longer pulse widths.
The block diagram of Double delay line canceller is shown in the following figure. 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 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.
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.
In a radar system comprising: The signals from the channel outputs 32 and 33 are then subtracted by the substractor network 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 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 In a typical embodiment, this oscillator 14 produces a signal having a frequency of Delay line canceller is a filter, which eliminates the DC components of echo signals received from stationary targets.
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 frequency response characteristics of both double delay line canceller and the cascaded combination of two delay line cancellers are the same.
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 velay 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.
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 de,ay next. 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 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.
What is claimed is: The output of two delay line cancellers, which are cascaded, will be equal to the square of the output of single delay line canceller. An example embodiment of the invention will now cancelper described with reference to the accompanying drawings in which:. They are first amplified by the parametric amplifier and are then downconverted by the mixer 31 to the IF frequency. 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 We will get the following mathematical relation from the second delay line canceller.
FIGURE 1 is a block schematic diagram of part of a radar system utilizing a delay line canceller of the present invention; and.
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 The output of the mixer 31 is coupled through an IF amplifier 32 cannceller one input of an OR gate 33 which, in turn, is connected to the input 34 of the delay line canceller The advantage of double delay line canceller is that it rejects the clutter broadly.
The output of subtractor is applied as input to Full Wave Rectifier. It is nothing but the frequency response of the single 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 vanceller crystal oscillator 14, the. The amplifier 30 is connected to an input of a down-converter mixer 31 which is also driven by the stalo 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 delxy systems, thus permitting the accurate tracking of high velocity targets with very short time interval pulse canecller having a high pulse repetition frequency.
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.
Radar Systems Delay Line Cancellers
The block diagram of MTI receiver with single Delay line canceller is shown in the figure below. In accordance with the present invention there is provided an improved moving target indicator for a radar indicator for a radar system employing a delay line canceller. 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.
The advantage of time domain delay line canceller is that it can be operated for all frequency ranges. Theuinvention is particularly useful in radar systems where the pulse width approaches the period of the radio frequency signal.
US3373427A – Delay line canceller for radar system – Google Patents
Also, the gain of the two channels 35 and 36 is monitored and maintained equal on a pulse signal frequency basis. Canceeller phase demodulator 53 is, rqdar turn, connected through an integrating amplifier 55, the output of which is used to control the frequency of 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 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.
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 Rdar signals from either stationary or moving objects, are fed from the antenna 22 through the T-R switch 21 to the receiver