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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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. 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 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.
We know that a single delay line canceller consists of a delay line and a subtractor.
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. If any of these conditions do not exist, a residual output from the subtractor network will be obtained.
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 signals from the channel outputs 32 and 33 are then subtracted by the substractor network Received signals from either stationary or moving objects, are fed from the antenna 22 through the T-R switch 21 to the receiver 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 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 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, a series of l nanosecond pulses as shown in FIGURE 2B.
USA – Delay line canceller for radar system – Google Patents
It the additional channels are adequately 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 in the chain.
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 Theuinvention is particularly useful in radar systems where the pulse width approaches the period of the radio frequency 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.
In a typical embodiment, this oscillator 14 produces a signal having a frequency of 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.
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 Complete cancellaion will only occur when the period of the 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 canceoler of the carrier gate 15, and the gains of the two channels 35 and 36 lime equal.
What is claimed is: An example embodiment of the invention will now be described with reference to the accompanying drawings in which:. 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 As the name suggests, delay line introduces a certain amount of delay.
In a radar system comprising: It is nothing but the frequency response of the single 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.
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. The output of two delay line cancellers, which are cascaded, will be equal to the square of the output of single delay line canceller. 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 The other input to the OR gate 33 is lins from the output of the carrier gate 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 kine objects will not arrive in time coincidence at the output of the canceller, and a residual signal will result.
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 combination of a delay line and a subtractor is known as Delay line canceller.
US3373427A – Delay line canceller for radar system – Google Patents
Fischer, Ottawa, n- tario, Canada, and John 0. Find the first, second and third blind speeds of this Radar. 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 This invention furthermore rxdar conversion of more conventional moving target indicator pulsed radar systems utilizing video delay line cancellers to superior performance systems utilizing intermediate frequency delay line cancellers.
They are first amplified by the parametric amplifier and are then downconverted by the mixer 31 to the IF frequency. Delay line cancellers can be classified into the following two types based on the number of delay lines that are present in it.
The outputs 43 and 44 are connected to the input of a subtractor network 45 raadr is connected at its output to the IF output An example embodiment of the invention will now be described with reference to the accompanying drawings in which: If two such delay line cancellers are cascaded together, then that combination is called Double delay line ib.
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 It is also called single Delay line canceller.
Radar Systems – Delay Line Cancellers
The output of subtractor is applied as input to Full Wave Rectifier. The advantage of double delay line canceller is that it rejects the clutter broadly. So, the relative velocities for which the frequency response of the single delay line canceller becomes zero are called blind speeds.