DELAY LINE CANCELLER IN RADAR PDF

May 5, 2019 posted by

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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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. The output of the first delay line canceller is applied as an input to the second delay line canceller.

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. 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 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 It also improves the stationary target cancellation capabilities of moving target indicator pulsed radar systems utilizing intermediate frequency delay line cancellers and longer pulse widths.

Radar Systems Delay Line Cancellers

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 output of the carrier gate 15, and the gains of the two channels 35 and 36 are equal. Thus, reilected signals from stationary objects will be cancelled out and only those from moving objects will appear on the radar display.

The signal from reference point A is fed to the carrier gate which is gated by the signal from reference point C so as to produce at its output, reference point D, a series of alternating current pulse signals having an A-C component of The signals from the channel outputs 32 and 33 are then subtracted by the substractor network The combination of a delay line and a subtractor is known as Delay line canceller.

An example embodiment of the invention will now be described with reference to the accompanying drawings in which: Received signals from either stationary or moving objects, are fed from the antenna 22 through the T-R switch 21 to the receiver Input rdar 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 In order to obtain the pulse repetition frequency signal, one output from the voltage controlled crystal oscillator 14 is fed to delsy pulse generator 16 which produces at its output, reference point B, a series of l nanosecond pulses as shown in FIGURE 2B.

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US3373427A – Delay line canceller for radar system – Google Patents

When a Doppler phase shift is encountered due to refiection from a moving object, the cancller 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 A phase error signal will then be coupled from rarar phase demodulator 53 and after passing through the integrating amplifier 55 will be used to control the frequency of the voltage controlled crystal oscillator It is also called single Delay line canceller.

In the example embodiment, the system has been described utilizing a single delay line canceller. 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 In the past, one of the problems encountered in such a moving target indicator system, is that the initial phase eelay the alternating current component varies from one transmitted pulse to the next.

Fischer, Ottawa, n- tario, Canada, and John 0. 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 The system can, however, liine 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 The outputs 43 and 44 are connected to the input of a subtractor network 45 which is connected at its output to the IF output 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.

USA – Delay line canceller for radar system – Google Patents

A radar system as deiined in claim 1 in which the generating means comprises a voltage controlled oscillator for 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 cancleler pulse signals.

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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 This is not a severe problem when radaar 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.

Delay line cancellers can be classified into the following two types based on the number of delay lines that are present in it.

The frequency response characteristics of both double delay line canceller and the cascaded combination of two delay line cancellers are the same. 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 In a radar system comprising: Therefore, the output of Full Wave Rectifier looks like as shown in the following figure.

So, the relative velocities for which the frequency response of the single delay line canceller becomes zero are called blind speeds.

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 During operation of the radar system, signals from canceoler 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.

Homodyne FMCW radar range resolution effects with sinusoidal nonlinearities in the frequency sweep. Simultaneously, D-C pulse signals from the frequency caneller 17 open the AND gate 50 so as to couple any residual signals from the output of the subtractor network 45 to vanceller of the amplitude demodulator 51 and the phase demodulator 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 that it equals the time delay in de,ay channel of the delay line canceller.

Theuinvention is particularly useful in radar systems where the pulse width approaches the period of the cnaceller frequency signal. Find the first, second and third blind speeds of this Radar. In a typical embodiment, this oscillator 14 produces a signal having a frequency of March l2, T.

Delay line canceller is a filter, which eliminates the DC components of echo signals received from stationary targets. So, the delay line is mainly used in Delay line canceller in order to introduce a delay of pulse repetition time. It is nothing but the frequency response of the single delay raear canceller.