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 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 As the name suggests, delay line introduces a certain amount of delay.
USA – Delay line canceller for radar system – Google Patents
The output of the first delay line canceller is applied as an input to the second delay line canceller. We will get the following mathematical relation from first delay line canceller. Since canceloer 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.
Thus, reilected signals from stationary objects will be cancelled out and only those from moving objects will appear on the radar display.
The signals from the channel outputs 32 and 33 are then subtracted by the substractor network 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 An example embodiment of the invention will now be described with reference to the accompanying drawings in which:.
The block diagram of MTI receiver with single Delay line canceller is shown in the figure below. The advantage of double delay line canceller is that it rejects the clutter broadly. We know that a single delay line canceller consists of a delay line and a subtractor. So, the relative velocities for which the frequency response of the single delay line canceller becomes zero are called blind speeds.
US3373427A – Delay line canceller for radar system – Google Patents
Thus, successive pulses will appear in phase at the outputs 43 and 44 and will thus he cancelled at the IF output 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 Received signals from either stationary or moving objects, are fed from the antenna 22 through the T-R switch 21 to the receiver Cancelelr one embodiment of such a system, the invention includes means for controlling ljne 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.
In a typical embodiment, this oscillator 14 produces a signal having a frequency of 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 a residual signal will result.
Delay line canceller is a filter, which eliminates the DC components of echo signals received from stationary targets. It is also called single Delay line canceller.
This produces a control signal at the cancellers output which is used to control the periodI delah the transmitted pulse signals so that the period is fully synchronized with the time delay encountered in the canceller.
The system can, however, be readily extended to multiple delay cancellrr 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 In the example embodiment, the system has been described utilizing a single delay line canceller.
Radar Systems – Delay Line Cancellers
In a radar system, any received signal reilected from a stationary object will be exactly similar, in magnitude and phase, to the preceding one, being displaced from it in time by the period of successive transmitter pulses. If any of these conditions do not exist, a residual output from the subtractor network will be obtained. Complete cancellaion will only occur when the period of on signal from the carrier gate 15 is equal to the time delay of the delay line 41, the initial phase of the alternating current component of each pulse signal at D is a constant, the received IF signals reflected from targets are identical in frequency to those at the output of the carrier gate 15, and the gains of the two channels 35 and 36 are equal.
In a radar system comprising: 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, rzdar series of l nanosecond pulses as shown in FIGURE 2B. FIGURE 1 is a block cahceller diagram of part of a radar system utilizing a delay line canceller of the present invention; 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 eadar returned from stationary targets will cancel out.
Radar Systems Delay Line Cancellers
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. 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 Find the first, second and third blind speeds of this Radar.
The frequency response characteristics of both double delay line canceller and the cascaded combination of two delay line cancellers are the same. 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.
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.
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. 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 pulse repetition rate of 6.