Continuous wave (cw) radar system for phase-coded time delayed transmit-receive leakage cancellation

Patent metadata

Field	Value
Publication number	US-2020011985-A1
Application number	US-201715830560-A
Country	US
Kind code	A1
Filing date	Dec 4, 2017
Priority date	Mar 31, 2017
Publication date	Jan 9, 2020
Grant date	—

Abstract

Disclosed is a method, system, and apparatus for transmitting a randomly phase-coded CW waveform in a manner that suppresses signal leakage and enables the recovery of polyphase subcodes advantageous for the purposes of correlation and pulse compression. The CW system transmits and receives a random waveform while concurrently providing properly delayed phase conversion parameters (ϕi−θi) from a corrections generator to various range gates. Each range gate processes any echo returns using a most recent phase conversion parameters (ϕk−θk) provided and correlation of the resulting echo subcodes ϕR produce either target indications or noise signals, depending on the most recent phase conversion parameters (ϕk−θk) provided to the range gate. The system may transmit the randomly phase-coded CW waveform while recovering any phase code {ϕ1, ϕ2, . . . ϕN} that lends itself to advantageous pulse compressions.

First claim

What is claimed is:

1 . A method of transmitting a continuous wave phase-modulated random radar signal and processing echo returns comprising:
generating the continuous wave phase-modulated random radar signal by:
generating a random subcode θ i ;
producing a polyphase subcode ϕ i corresponding to the random subcode θ i where the polyphase subcode ϕ i is a member of a set of polyphase subcodes having N number of members;
transmitting a modulated subcode θ′ i from an antenna system during a subpulse width τ where τ is a measure of time, and where the modulated subcode θ′ i is an electromagnetic signal having a phase over the subpulse width τ, where the phase is based on the random subcode θ i ;
generating a phase conversion parameter (ϕ i −θ i ) using the random subcode θ i and the polyphase subcode ϕ i and providing the phase conversion parameter (ϕ i −θ i ) to a plurality of range gates comprising two or more range gates RG j , where j is an integer unique to each range gate RG j and j is greater than or equal to 1, by providing the phase conversion parameter (ϕ i −θ i ) to the each individual range gate RG j following a delay D j after transmission of the modulated subcode θ′ i from the antenna system, where the delay D j is unique to the each individual range gate RG j ; and
repeating the generating the random subcode θ i step, the producing the polyphase subcode ϕ i step, the transmitting the modulated subcode θ′ i step, and the generating the phase conversion parameter (ϕ i −θ i ) using the random subcode θ i and the polyphase subcode ϕ i and providing the phase conversion parameter (ϕ i −θ i ) step, thereby transmitting the continuous wave phase-modulated random radar signal; and
receiving an echo return of the continuous wave phase-modulated random radar signal and processing the echo return using the plurality of range gates RG j , thereby processing echo returns.

2 . The method of claim 1 where receiving the echo return of the continuous wave phase-modulated random radar signal and processing the echo return using the plurality of range gates RG j further comprises:
receiving the echo return from the antenna system;
demodulating the echo return and producing a demodulated subcode θ R ; and
providing the demodulated subcode θ R to the plurality of range gates RG j .

3 . The method of claim 2 further comprising processing the demodulated subcode θ R by, at the each range gate RG j by performing steps comprising:
receiving the demodulated subcode θ R ;
identifying a most recent phase conversion parameter (ϕ k −θ k ) received from the corrections generator, where the most recent phase conversion parameter (ϕ k −θ k ) is the phase conversion parameter (ϕ i −θ i ) most recently provided to the each range gate RG j ;
generating an echo subcode ϕ R by converting the demodulated subcode θ R using the most recent phase conversion parameter (ϕ k −θ k );
modifying a polyphase sequence comprising a string of subcodes by adding the echo subcode ϕ R to the polyphase sequence, thereby generating an updated polyphase sequence; and
correlating the updated polyphase sequence using the set of polyphase subcodes having N number of members used by the polyphase subcode generator, thereby processing the demodulated subcode θ R .

4 . The method of claim 3 where the each range gate RG j has an associated D RG(j) where the associated D RG(j) is equal to 2τ(j)+ΔT P , where ΔT P is a period ΔT P based on an echo processing delay, and where 0.8≤D j /D RG(j) ≤1.2, where D j is the delay D j unique to the each range gate RG j and D RG(j) is the associated D RG(j) for the each range gate RG j .

5 . The method of claim 4 further comprising providing the demodulated subcode θ R to the plurality of range gates RG j over the period ΔT P .

6 . The method of claim 5 where correlating the updated polyphase sequence using the set of polyphase subcodes having N number of members comprises correlating the updated polyphase sequence using a matched filter comprising a reference register, where the reference register comprises the set of polyphase subcodes having N number of members used by the polyphase subcode generator, thereby processing the demodulated subcode θ R .

7 . The method of claim 5 where generating the phase conversion parameter (ϕ i −θ i ) using the random subcode θ i and the polyphase subcode ϕ i comprises performing operations equivalent to (ϕ i −θ i )=f 1 (ϕ i , θ i ) where f 1 is a mathematical function over at least some portion of a domain comprising ϕ i and θ i , and where (ϕ i −θ i ) is the phase conversion parameter (ϕ i −θ i ), ϕ i is the polyphase subcode ϕ i , and θ i is the random subcode θ i .

8 . The method of claim 7 where generating the echo subcode ϕ R by converting the demodulated subcode θ R using the most recent phase conversion parameter (ϕ k −θ k ) comprises performing operations equivalent to ϕ R =f 2 ((ϕ k −θ k ), θ R ), where f 2 is a mathematical function over at least some portion of a domain comprising (ϕ k −θ k ) and θ R and where when 0.8≤θ i /θ R ≤1.2 and 0.8≤(ϕ i −θ i )/(ϕ k −θ k )≤1.2, then 0.8≤ϕ i /ϕ R ≤1.2, where θ R is the demodulated subcode θ R , (ϕ k −θ k ) is the most recent phase conversion parameter (ϕ k −θ k ), and ϕ R is the echo subcode θ R .

9 . The method of claim 5 where the continuous wave phase-modulated random radar signal comprises a plurality of random subcodes θ i where the plurality of random subcodes θ i defines a plurality of phases over a time period T, and each phase comprising the plurality of phases satisfies a relationship 0.8≤p/x PDF ≤1.2, where p is the each phase comprising the plurality of phases and x PDF is a point on a probability density function (μ,τ 2 ).

10 . A system for transmitting a randomly modulated subcode and processing echo returns:
a transmitting system comprising:
a random waveform generator receiving a random noise signal and generating a random subcode θ i , where the random subcode θ i has a subpulse width τ where τ is a measure of time;
a polyphase subcode generator producing a polyphase subcode ϕ i corresponding to the random subcode θ i where the polyphase subcode ϕ i is a member of a set of polyphase subcodes having N number of members;
an antenna system transmitting a modulated subcode θ′ i at a time t i , where the modulated subcode θ′ i is an electromagnetic signal having a frequency and having a phase over the subpulse width τ dependent on the random subcode θ i , thereby transmitting the randomly modulated subcode; and
a corrections generator performing steps comprising:
receiving the random subcode θ i from the random waveform generator;
receiving the polyphase subcode ϕ i from the polyphase subcode generator; and
generating a phase conversion parameter (ϕ i −θ i ) using the random subcode θ i and the polyphase subcode ϕ i and providing the phase conversion parameter (ϕ i −θ i ) to a plurality of range gates comprising two or more range gates RG j , where j is an integer unique to each range gate RG j and j is greater than or equal to 1, by providing the phase conversion parameter (ϕ i −θ i ) to the each range gate RG j following a delay D j after transmission of the modulated subcode θ′ i from the antenna system, where the delay D j is unique to the each range gate RG j ;

the antenna system receiving an echo return of the modulated subcode θ′ i transmitted by the antenna system; a demodulator receiving the echo return and demodulating the echo return to produce a demodulated subcode θ R , and providing the demodulated subcode θ R to the plurality of range gates; the each range gate RG j receiving the demodulated subcode θ

Assignees

• Us Navy

Inventors

• Jenn David C
• Pace Phillip E
• Romero Ric A

Classifications

• G01S7/4021

  of receivers · CPC title

• G01S13/325 Primary

  using transmission of coded signals, e.g. P.S.K. signals · CPC title

• G01S13/38 Primary

  wherein more than one modulation frequency is used · CPC title