RADIANT ENERGY RECEIVER CIRCUITS

• US 3,878,527 A
• Filed: 10/07/1970
• Issued: 04/15/1975
• Est. Priority Date: 10/07/1970
• Status: Expired due to Term

• Current Assignee: ITT Corporation (ITT, Inc.)
• Original Assignee: Ernest Isaac Rensin, Tom Schnerk
• Inventors: Rensin, Ernest Isaac, Schnerk, Tom
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/078,790
• Time in Patent Office: 1,651 Days
• Field of Search: 343/7.7 331/1A 325/421
• US Class Current: 342/103
• CPC Class Codes: G01S 13/586 using, or combined with, frequency tracking means

Abstract

A pseudonoise receiver having both a search and a track mode performed in that sequence after the incoming signal has been acquired, wherein the search mode is rendered effective by a slight mismatch in phase or frequency of the receiver internal code, and the code on the incoming carrier. In accordance with the foregoing, positive signal acquisition is made possible within a very short time.

Claims

1. A pseudonoise receiver comprising:

first means to receive an incoming first signal, a pseudonoise coded carrier;

said first means including second means to decode said first signal when a second signal is applied to said second means, said second signal comprising a series of pulses having a code and code phase the same as that of the carrier code, said second means producing a third output signal including the decoded carrier when said second signal is impressed on said second means;

a variable frequency first oscillator adapted to oscillate at a frequency as a function of an input thereto;

third means responsive to said third signal to provide a fourth signal of a magnitude to drive said first oscillator so that the frequency thereof continuously follows the clock frequency of the carrier code;

a first switch actuable to supply a substantially constant fifth signal to the said input of said first oscillator;

a second switch actuable to impress said fourth signal on said first oscillator input;

fourth means to acutate said first switch and to deactuate said second switch when the magnitude of said third signal is less than a predetermined level, and to deactuate said first switch and to actuate said second switch when the magnitude of said third signal is greater than said predetermined level; and

fifth means responsive to the output of said first oscillator for producing an internal serial pulse code the same as that of the carrier code and of a clock frequency which is a function of that of said first oscillator, said second means being connected from said fifth means to receive said internal code therefrom, said fifth signal being of a magnitude to cause said internal code to be generated at a clock frequency different from that of the carrier code.

2. The invention as defined in claim 1, wherein said fifth means produces said internal code with a clock frequency equal to that of said first oscillator, said second means including a first mixer being connected from the output of said first means, said second means including a second mixer having its output connected to another input of said first mixer, a local oscillator connected to one input of said second mixer, third and fourth switches connected from the Output of said fifth means, a delay device connected from the output of said third switch to the other second mixer input, said fourth switch being directly connected to said other second mixer input, an astable multivibrator having first and second outputs connected to said third and fourth switches, respectively, to actuate said third and fourth switches only alternately, a filter connected from the output of said first mixer to pass the oscillation frequency of said multivibrator, a phase detector within said third means connected from said filter and one output of said multivibrator to said second switch, said fourth means including a threshold detector connected from said first mixer, said predetermined level being the threshold level of said detector, said fourth means including sixth means connected from said threshold detector to actuate said first and second switches only alternately, said fifth means including a code generator connected from the output of said first oscillator to said third and fourth switches.

3. The invention as defined in claim 1, wherein said second means includes a first mixer, a second mixer connected from the output of said first mixer, an amplifier connected from the output of said second mixer, a frequency discriminator connected from the output of said amplifier, a variable frequency second oscillator connected from the output of said discriminator, the output of said second oscillator being connected to another input of said second mixer, an amplitude modulation detector connected from the output of said amplifier, an astable multivibrator, a phase detector connected from the ouputs of said multivibrator and said amplitude modulation detector, the output of said phase detector being connected to said second switch, a threshold detector responsive to said third signal, said fourth means including sixth means to actuate said first and second switches only alternately, said predetermined level being the threshold level of said threshold detector, a third mixer having first and second inputs connected, respectively, from the outputs of said first and second oscillators, a filter connected from the output of said third mixer, a squarer connected from the output of said filter, a frequency divider connected from the output of said squarer, a clock having a frequency slightly different from the received code frequency, a tapped delay line connected from said clock, a commutator connected from the delay line taps, said commutator being connected from said divider to change the phase of said clock frequency in accordance with the frequency of the output sginal of said divider, a code generator within said fifth means connected from said commutator, and seventh means connected from said code generator and said multivibrator to said first mixer for impressing a serial pulse code on said first mixer which has a phase that oscillates about a mean at a frequency equal to the oscillation frequency of said multivibrator.

4. In a pseudonoise receiver, the combination comprising:

first means responsive to an incoming carrier signal having a serial pulse code thereon and to a similar internal serial pulse code for producing an output signal in accordance with the relative phases of said codes;

second means to impress said internal code on said first means with a phase oscillation about a predetermined mean; and

third means responsive to a signal in the output of said first means having a frequency equal to the second harmonic of the said phase oscillation frequency to shift the frequency of said internal code in a direction tending to maintain the output signal strength of said first means at a peak, said second means including a first variable frequency oscillator, a code generator connected from the output of said first oscillator, and fourth means connected from the output of said code generator to the input of said first means to oscillate the phase of the output code of said generator.

5. The invention as defined in claim 4, wherein said firsT means includes a mixer a first input to receive the coded carrier, a second input to receive said internal code, and an output, said code generator producing a serial pulse code the same as that of said carrier but at a frequency equal to that of said first oscillator, a second oscillator, said fourth means being responsive to the output of said code generator and to the output of said second oscillator to impress the code of said code generator on said second mixer input with a phase modulation frequency equal to the oscillation frequency of said second oscillator, said third means having an output connected to the input of said first oscillator.

6. The invention as defined in claim 5, wherein said third means includes a phase detector, the output of said phase detector being connected to the input of said first oscillator, said phase detector having two inputs connected from the output of said mixer and the output of said second oscillator, respectively.

7. In a system utilizing a pseudonoise coded carrier wave reflected from a moving target, a receiver comprising:

first means responsive to the coded reflected wave and to an internal code to produce a first signal which is the decoded carrier;

second means responsive to said first signal to produce a second alternating signal of a frequency which is a function of the frequency of the Doppler of the carrier; and

third means responsive to said second signal to supply said internal code to said first means with a frequency which is a function of said carrier Doppler frequency.

8. The invention as defined in claim 7, wherein said second signal is the carrier Doppler, said third means including fourth means actuable to provide a serial pulse code similar to that of the received code and of approximately the same frequency as the received code, but continuously shifted in phase in direct proportion to said carrier Doppler frequency, and fifth means to actuate said third means at a switching rate to shift said code phase, said means being adapted to control said fourth means at a PRF which is a fraction of said carrier Doppler frequency.

9. The invention as defined in claim 8, wherein said fourth means includes a delay line having a predetermined number of equally spaced taps, a commutator connected from said delay line, a coder connected from said commutator, said first means being responsive to the output of said coder, the product of said number of taps and said fraction being approximately equal to the ratio of the code frequency to the carrier frequency.

10. The invention as defined in claim 7, wherein said first means includes a first mixer, said second means including a second mixer having one input connected from the output of said first mixer, an amplifier, a frequency discriminator and a first variable frequency oscillator connected in succession from the output of said second mixer to another input thereto, a second oscillator, a third mixer having first and second inputs connected from said first and second oscillators, respectively, said third mixer having an alternating output signal of a frequency equal to the Doppler of the carrier.

11. The invention as defined in claim 10, including means responsive to the ouput of said amplifier to vary the frequency of said second oscillator.

12. The invention as defined in claim 7, wherein said third means is actuable to produce a variation in the internal code frequency in direct proportion to the product of the carrier Doppler frequency and the ratio of the code frequency to the carrier frequency.

13. In a pseudonoise receiver, apparatus for searching for the incoming signal including a pulse coded carrier comprising:

first means responsive to said coded carrier and to an internal serial pulse code for producing an output signal;

second means for impressing said internal code on said first means with an approximately constant clock frequency differing slightly from the frequency of said carrier code to shift tHe phase of said internal code gradually until said internal code and said carrier code are substantially aligned;

third means actuable to track said carrier code;

fourth means connected to receive said output signal from said first means, said fourth means being adapted to actuate said third means when said output signal exceeds a predetermined level; and

fifth means actuable to produce ocillation of the phase of said internal code about a mean phase value substantially equal to the phase at which said first means ouput signal exceeds said predetermined level.