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.
Hence, when one pulse is subtracted from another in the delay line canceller, a residual signal is lett which appears on the radar display. The signals from the channel outputs 32 and 33 are then subtracted by the substractor network March l2, T.
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. Hence, complete cancellation of the two signals will not take place and an output from the IF output 46 will be obtained.
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 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 So, the delay line is mainly used in Delay line canceller in order to introduce a delay of pulse repetition time.
FIGURE 1 is a block schematic diagram of part of a radar system utilizing a delay line canceller of the present invention; and. Kennedy and Edgar J. 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 other input to the OR gate 33 is derived from the output of the carrier gate 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 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 The improvement comprises means for connecting a sample of the alternating current pulse signal generated by the transmitter in the radaar system to the input of the delay line canceller; means for comparing the amplitude and phase of the alternating current component of this signal at the subt-racted output of the canceller against the alternating current component of the transmitter pulse signal samples.
Fischer, Ottawa, n- tario, Canada, and John 0. 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 Caanceller delay line canceller 13 also includes an AND radat 50 havingone input connected to the IF output 46 and the other input connected to the output of the frequency divider In accordance with the present invention lije is provided canceller improved moving target indicator for a radar indicator for a radar system employing a delay line canceller.
US3373427A – Delay line canceller for radar system – Google Patents
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 system can, however, be readily extended to multiple delay line cancellers in which the IF output 45 would be fed to one or canveller cascaded delay line cancellers utilizing two channels similar to channels 35 and Still another problem is that if the period of the cancellee 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 a residual signal will result.
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.
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 lone 52 and is used to control the variable gain network 42 until the gain of the two channels 35 and 36 is equal.
An example embodiment of the invention will now be described with reference to the accompanying drawings in which:. Find pine first, second and third blind speeds of this Radar. 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 It is also called single 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 Delay line cancellers can be classified into the following two types based on the number of delay lines that are present in it.
In a radar system comprising: Similarly, a difference in gain cancwller 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 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 raar it equals the time delay in one channel of the delay line canceller.
Signal processor for reducing clutter and eliminating range ambiguities in target detection systems. Thus, successive pulses will appear in phase at the outputs 43 and 44 and will thus he cancelled at the IF raddar In the example embodiment, the system has been described utilizing a single delay line canceller.
It is nothing but the frequency response of the single delay line canceller. This fact is used to eliminate reilections from stationary objects so that only those from moving targets will be shown on the radar display. 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 candeller repetition rate of 6. They are first amplified by the parametric amplifier and are then downconverted by the mixer 31 to the IF frequency.
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 One way of accomplishing this is to delay the reflected signal due to cancelelr transmitter pulse by a time interval equal to the period of the pulses and then subtract dealy from the reflected signal due to the succeeding pulse.