Accurate normalization for a monopulse radar

• US 3,921,173 A
• Filed: 08/14/1974
• Issued: 11/18/1975
• Est. Priority Date: 08/14/1974
• Status: Expired due to Term

• Current Assignee: Don N. Thomson
• Original Assignee: Don N. Thomson
• Inventors: Thomson, Don N.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/497,434
• Time in Patent Office: 461 Days
• Field of Search: 343/16M,17.7
• US Class Current: 342/92
• CPC Class Codes: G01S 13/4436 with means specially adapted to maintain the same processing characteristics between the monopulse signals
• CPC Class Codes: G01S 7/34 Gain of receiver varied automatically during pulse-recurrence period, e.g. anti-clutter gain control

Abstract

The invention comprises a system for controlling and normalizing the gain of the difference I.f. I.F. to the gain of the sum I.F. amplifier in a monopulse radar. A pulsed, I.F., pilot signal is applied to both the sum and difference I.F. amplifiers at predetermined intervals chosen so that the pilot signal does not interfere with the echo return signal. The outputs from these I.F. amplifiers are gated at the predetermined intervals coinciding with the application of the I.F. pilot signal. These gated, sum-and difference-amplifier, pilot signals are envelopedetected and then applied to a differential amplifier. This differential amplifier generates a signal representative of the difference between the sum and difference amplifier pilot signals and applies this signal to the difference, I.F. amplifier to control its gain. The sum I.F. amplifier has a conventional A.G.C. system for gain control. The control signal generated by this conventional A.G.C. system is also applied to a circuit for controlling the signal level of the I.F. pilot signal so it is inversely proportional to the signal gain level of the sum I.F. amplifier. This controlled I.F. pilot signal is then applied to the sum and difference I.F. amplifiers (as stated above) via a hybrid network and directional couplers, at a time chosen so that it does not interfere with the predicted echo-return.

Claims

1. An automatic gain control and normalization system for equalizing the gains of the sum and difference I.F. amplifiers in a monopulse radar system comprising:

first I.F. amplifier means;

second I.F. amplifier means;

means for generating an I.F. difference voltage and an I.F. sum voltage from the R.F. signals from a plurality of antennas in a monopulse radar system and applying the I.F. difference voltage as an input to said first I.F. amplifier means and applying the I.F. sum voltage as an input to said second, I.F. amplifier means;

third I.F. amplifier means;

first A.G.C. means, with its input coupled to the output of said second I.F. amplifier means, for generating a control signal, and applying the control signal to said second I.F. amplifier means and to said third I.F. amplifier means to control their signal levels;

means coupled to said first A.G.C. means for preventing the latter from responding to any signal except an I.F. sum signal;

fourth I.F. amplifier means with its output coupled to the input of said third I.F. amplifier means;

signal generator means for generating an I.F. pilot signal and applying this I.F. pilot signal to said fourth I.F. amplifier means at predetermined intervals chosen so that said pilot signal does not interfere with an I.F. sum or difference voltage;

second A.G.C. means, with its input coupled to the output of said third I.F. amplifier means, for comparing its input signal to a reference, generating a control signal, and applying this control signal to said fourth I.F. amplifier means to control its gain such that it is inversely proportional to the gain of said third I.F. amplifier means;

means for electrically coupling the output signal from said fourth I.F. amplifier means to the inputs of said first and said second I.F. amplifier means;

first gate means with its input coupled to the output of said first, I.F. amplifier means;

second gate means with its input coupled to the output of said second I.F. amplifier means, said first and second gate means being open only during the predetermined times when said I.F. pilot signal is generated by said signal generator means; and

comparing means connected to the outputs from said first and said second gate means for comparing their signal outputs and applying an error signal to said first I.F. amplifier means to control its signal level.

2. An automatic gain control and normalization system as defined in claim 1, wherein said signal generator means comprises:

an I.F. signal generator; and

a gate to which the I.F. pilot signal generated by said signal generator is applied and to which a timing signal is applied to open the gate at predetermined intervals.

3. An automatic gain control and normalization system as defined in claim 1 wherein said first and second A.G.C. means comprise:

a differential amplifier, said differential amplifier having a reference voltage applied to one of its inputs; and

envelope detecting means for detecting the envelope of the input signal and producing a DC signal from the envelope and applying this DC signal to the other input of said differential amplifier.

4. An automatic gain control and normalization system as defined in claim 1, wherein said comparing means comprises:

a differential amplifier;

first envelope detector means with its input connected to the output of said first gate means for detecting the envelope of this output and producing a DC signal from this envelope and applying this DC signal to one of the inputs of said differential amplifier;

second envelope detector means with its input connected to the output of said second gate means for detecting the envelope of This output and producing a DC signal from this envelope and applying this DC signal to the other input of said differential amplifier.

5. An automatic gain control and normalization system as defined in claim 1, wherein said means to electrically couple the output signal from said fourth I.F. amplifier means is a hybrid circuit.

6. An automatic gain control and normalization system as defined in claim 1, wherein said first and second I.F. amplifier means are I.F. amplifiers.

7. An automatic gain control and normalization systems as defined in claim 1, wherein said first and second I.F. amplifier means each comprise:

a digital attenuator to which said control signals are applied to provide signal level control by means of signal attenuation;

an I.F. amplifier with its input coupled to the output of said digital attenuator.

8. An automatic gain control and normalization system for equalizing the gains of the sum and difference I.F. amplifiers in a monopulse radar system comprising:

first I.F. amplifier means;

second I.F. amplifier means;

means for generating an I.F. difference voltage and an I.F. sum voltage from the R.F. signals from a plurality antennas in a monopulse radar system and applying said I.F. difference voltage as an input to said first I.F. amplifier means and applying said I.F. sum voltage as an input to said second I.F. amplifier means;

target A.G.C. means, with its input coupled to the output of said second I.F. amplifier means, for generating a control signal, and applying this control signal back to said second I.F. amplifier means to control its signal level;

means connected to said target A.G.C. preventing said target A.G.C. means from responding to any signal except an I.F. sum signal;

means connected to the output from said target A.G.C. means for generating an I.F. pilot signal at predetermined intervals chosen so that said I.F. pilot signal does not interfere with said I.F. sum and difference signals, said I.F. pilot signal having a signal level inversely proportional to the signal level at the output of said second I.F. amplifier means;

means for electrically coupling the I.F. pilot signal to the inputs of said first and said second I.F. amplifier means;

differential A.G.C. means with one of its inputs connected to the output of said first I.F. amplifier means and with another of its inputs connected to the output of said second I.F. amplifier means, said differential A.G.C. means generating a difference signal representative of the difference between said first and second I.F. amplifier outputs only during the predetermined intervals during which said I.F. pilot signal is generated, said differential A.G.C. means applying this difference signal to said first I.F. amplifier means to control its gain.

9. An automatic gain control and normalization system as defined in claim 8, wherein said means for generating an I.F. pilot signal comprises:

third I.F. amplifier means coupled to the output from said target A.G.C. means so that the target A.G.C. control signal controls the gain of said third I.F. amplifier means;

fourth I.F. amplifier means with its output coupled to the input of said third I.F. amplifier means;

signal generator means for generating an I.F. pilot signal;

first gate means with its input coupled to the output of said signal generator means, and with its output connected to the input of said fourth I.F. amplifier means, said first gate means opening to permit the I.F. pilot signal to reach said fourth I.F. amplifier means only during said predetermined intervals;

pilot A.G.C. means, with its input coupled to the output of said third I.F. amplifier means, for comparing this input signal to a reference voltage, generating a control signal, and applying this control signal to said fourth I.F. amplifier means to control its signal level.

10. An auTomatic gain control and normalization system as defined in claim 8, wherein said differential A.G.C. means comprises:

first gate means with its input coupled to the output of said first I.F. amplifier means;

second gate means with its input coupled to the output of said second I.F. amplifier means, said first and second gate means being open only during said predetermined times when the I.F. pilot signal is generated by said means for generating an I.F. pilot signal;

comparing means connected to the outputs from said first and second gate means for comparing the signals from said first and second gate means and applying a control signal representative of the difference between the signals from said first and second gate means to said first I.F. amplifier means to control its signal level.

11. A method for controlling and normalizing the gains of the sum and difference I.F. amplifying means in a monopulse radar system comprising the steps of:

applying an I.F. pilot signal to said sum and difference I.F. amplifying means at predetermined intervals chosen so that said pilot signal does not interfere with any echo return signals;

generating a difference signal representative of the difference between the I.F. pilot signal output from said sum I.F. amplifying means and said difference I.F. amplifying means;

applying this generated difference signal to said difference I.F. amplifying means to control and normalize its gain to that of the sum I.F. amplifying means;

generating a first control signal from the output of said sum I.F. amplifying only when an echo return signal is present and applying said first control signal back to control the signal level of said sum I.F. amplifying means; and

utilizing said first control signal also to control the signal level of said I.F. pilot signal to that it is inversely proportional to the output signal level of said sum I.F. amplifying means.

12. A method as defined in claim 11 wherein said step of generating a difference signal comprises the steps of:

gating the output signals from said sum and difference I.F. amplifying means only at the predetermined intervals coinciding with the application of said I.F. pilot signal;

detecting the envelopes of these gated output signals;

filtering a DC signal from these detected envelopes;

generating a difference signal from said DC, signals representative of the difference between the gated sum-I.F.-amplifier, signal envelope and the difference-I.F.-amplifier, signal envelope.

13. A method as defined in claim 11 wherein said step of utilizing said control signal comprises the steps of:

generating an I.F. pilot signal;

gating said I.F. pilot signal at predetermined intervals to a first I.F. amplifier;

amplifying said I.F. pilot signal in said first I.F. amplifying means and applying said amplified I.F. pilot signal to a second I.F. amplifying means;

controlling the gain of said second I.F. amplifying means with said first control signal;

generating a second control signal from the output from said second I.F. amplifier;

applying said second control signal to said first I.F. amplifying means to control its gain;

applying the output from said first I.F. amplifying means to said sum and difference I.F. amplifying means.