# US 5,347,120 A · Method and apparatus for pulsed-laser detection

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- Number: US 5,347,120 A
- Document ID: US5347120A
- Status: Granted
- Kind: A
- Application number: 08/053,468
- Filed: 1993-04-27
- Granted: 1994-09-13
- Earliest claimed: 1992-05-28
- Assignees: Cincinnati Microwave, Inc.
- Inventors: Lawrence G. Decker; Janet R. Poston; Edward F. Hume
- Web page: https://patentgrep.com/patent/US5347120A

## CPC

- G01S 7/4804: {Auxiliary means for detecting or identifying lidar signals or the like, e.g. laser illuminators}
- G01S 7/483: Details of pulse systems
- G01S 7/495: Counter-measures or counter-counter-measures {using electronic or electro-optical means}
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

A method and apparatus for determining the strength and proximity of a pulsed-laser radar signal is provided. A photodetector detects signals and provides the signals to a decision network. The decision network evaluates the signals and generates an output pulse when a detected signal is a valid signal according to predetermined criteria implemented in the decision network. A processor is coupled to the decision network for counting output pulses. A threat indicator is driven by the processor in proportion to the output pulse count.

## Claims

### Claim 1

A method for determining the strength and proximity of a pulsed-laser radar signal which has been detected by a radar detection apparatus, said radar detection apparatus comprising a photodetector, a decision network coupled to the photodetector, a processor coupled to the decision network, and a threat indicator coupled to the processor, the method comprising:
evaluating the detected signal with the decision network, said decision network generating an output pulse when the detected signal is a valid signal according to predefined criteria implemented in the decision network;
counting output pulses which occur for consecutive detected signals with the processor;
providing a look-up table in the processor having predetermined values therein;
looking up the count in the look-up table and generating a value which corresponds to the count; and
driving the output level of the threat indicator in proportion to the generated value.

### Claim 2 (depends on 1)

The method of claim 1, wherein the evaluating step comprises:
comparing the magnitude of the detected signal to a reference magnitude and generating a first logic output which is true if the magnitude of the detected signal exceeds the reference magnitude and which is false otherwise;
comparing the pulse width of the detected signal to a reference pulse width and generating a second logic output which is false if the pulse width of the detected signal exceeds the reference pulse width and which is true otherwise; and
generating the output pulse when the first logic output is true and the second logic output is false.

### Claim 3

A pulsed-laser radar detection apparatus, comprising:
a photodetector;
a decision network coupled to the photodetector, said decision network generating an output pulse when a signal detected by the photodetector is a valid signal according to predefined criteria which are implemented in the decision network;
processing means coupled to the decision network, said processing means including means for counting output pulses which occur for consecutive detected signals, a look-up table having predetermined values therein, and means for looking up the count in the look-up table and generating a value which corresponds to the count; and
a relative threat indicator coupled to the processing means, wherein the indicator generates an indication having a characteristic which is proportional to the generated value.

### Claim 4 (depends on 3)

The apparatus of claim 3, wherein the indication is visual.

### Claim 5 (depends on 4)

The apparatus of claim 4, wherein the characteristic is volume.

### Claim 6 (depends on 4)

The apparatus of claim 4, wherein the characteristic is frequency.

### Claim 7 (depends on 3)

The apparatus of claim 3, wherein the indication is audible.

### Claim 8 (depends on 3)

The apparatus of claim 3, wherein said predetermined values are determined by a Gaussian probability density function for signal strength.

### Claim 9 (depends on 3)

The apparatus of claim 3, wherein the decision network comprises:
means for comparing the magnitude of the detected signal to a reference magnitude and generating a first logic output which is true if the magnitude of the detected signal exceeds the reference magnitude and which is false otherwise;
means for comparing the pulse width of the detected signal to a reference pulse width and generating a second logic output which is false if the pulse width of the detected signal exceeds the reference pulse width and which is true otherwise; and
means for generating the output pulse when the first logic output is true and the second logic output is false.

### Claim 10

An apparatus for detecting a valid pulsed-laser radar signal and for providing an indication of the relative strength and proximity of the detected signal, comprising:
a photodetector for detecting an optical signal and for converting it to an electrical signal;
a first amplifier coupled to the photodetector for boosting the electrical signal thereby creating a first signal V1;
an RC network coupled to the first amplifier for stretching the pulse width of the first signal V1 thereby creating a second signal V2;
a second amplifier coupled to the first amplifier for extracting a DC offset from the first signal V1 thereby creating a third signal V3;
a differential amplifier having a positive input coupled to the second signal V2 from the RC network, a negative input coupled to the third signal V3 from the second amplifier, and a threshold output;
a first comparator having a first input coupled to the threshold output, a second input coupled to the second signal V2 from the RC network, and a first logic output A;
a second comparator having a first input coupled to the threshold output, a second input coupled to the first signal V1 from the first amplifier, and a second logic output B;
a microprocessor coupled to the first logic output A from the first comparator and to the second logic output B from the second comparator, said microprocessor being programmed to evaluate the timing of logical values on outputs A and B, wherein the microprocessor further comprises means to count consecutive valid pulsed-laser signals, means to store the count, and means to provide a statistical correlation to signal strength and signal proximity based on the count; and
an alert indicator coupled to the microprocessor and having means for providing an alert indication that can vary in degree between a low level and a high level, wherein if output A is true and output B is false then a valid pulsed-laser signal is detected and the alert indicator is driven at a low level, and wherein the alert indicator is driven at a level that is determined by the statistical correlation of the count.