US4464662A — Determining azimuth of a transponder by measuring…

Claim 1

Independent Claim 310 words

A method for determining the azimuth of a radio wave transponder relative to a radar system having first and second receiving antennas located at a distance d from each other, comprising the steps of: a. transmitting from the radar system to the transponder a signal having a frequency which varies linearly with time; b. returning from the transponder a signal representative of the transmitted signal; c. receiving the returned signal at the first and second receiving antennas at times which differ in relation to any differences in the distances between said receiving antennas and the transponder; d. mixing the signal received at each of the first and second receiving antennas with the transmitted signal and producing first and second beat signals Fb 1 and Fb 2 having frequencies fb 1 and fb 2 , respectively; e. during a first interval following the transmission of a frequency F 1 at a time t 1 , measuring the sign and magnitude of the phase shift φ 0 between the signals Fb 1 and Fb 2 ; f. during a second interval following the transmission of a frequency F 2 at a time t 2 , measuring the sign and magnitude of the phase shift φ' 0 between the signals Fb 1 and Fb 2 , the timing of said first and second intervals being chosen such that the integral number of cycles of Fb 1 and Fb 2 between t 1 and t 2 are substantially equal; g. determining an overall phase variation Δφ by performing the calculation: Δφ=φ' 0 -φ 0 ; h. determining an approximate value φ.sub.Δφ for the phase shift between the signals Fb 1 and Fb 2 at the time t 1 by performing the calculation: ##EQU20## i. determining the value of a constant k to the nearest integer by performing the appropriate one of the following calculations:

Claim 2

Independent Claim 310 words

A method for determining the azimuth of a radio wave transponder relative to a radar system having first and second receiving antennas located at a distance d from each other, comprising the steps of: a. transmitting from the radar system to the transponder a signal having a frequency which varies linearly with time; b. returning from the transponder a signal representative of the transmitted signal; c. receiving the returned signal at the first and second receiving antennas at times which differ in relation to any differences in the distances between said receiving antennas and the transponder; d. mixing the signal received at each of the first and second receiving antennas with the transmitted signal and producing first and second beat signals Fb 1 and Fb 2 having frequencies fb 1 and fb 2 , respectively; e. during a first interval following the transmission of a frequency F 1 at a time t 1 , measuring the sign and magnitude of the phase shift φ 0 between the signals Fb 1 and Fb 2 ; f. during a second interval following the transmission of a frequency F 2 at a time t 2 , measuring the sign and magnitude of the phase shift φ' 0 between the signals Fb 1 and Fb 2 , the timing of said first and second intervals being chosen such that the integral number of cycles of Fb 1 and Fb 2 between t 1 and t 2 are substantially equal; g. determining an overall phase variation Δφ by performing the calculation: Δφ=φ' 0 -φ 0 ; h. determining an approximate value φ.sub.Δφ for the phase shift between the signals Fb 1 and Fb 2 at the time t 1 by performing the calculation: ##EQU20## i. determining the value of a constant k to the nearest integer by performing the appropriate one of the following calculations:

Claim 3

Dependent Claim 8 words

if the sign of Δφ is positive, ##EQU21##

Claim 4

Dependent Claim 8 words

if the sign of Δφ is positive, ##EQU21##

Claim 5

Dependent Claim 35 words

if the sign of Δφ is negative, ##EQU22## j. determining the accurate value of the phase shift φ between the signals Fb 1 and Fb 2 by performing the appropriate one of the following calculations:

Claim 6

Dependent Claim 35 words

if the sign of Δφ is negative, ##EQU22## j. determining the accurate value of the phase shift φ between the signals Fb 1 and Fb 2 by performing the appropriate one of the following calculations:

Claim 7

Dependent Claim 34 words

if the sign of Δφ is positive, φ=φ 0 +2kπ 2. if the sign of Δφ is negative, φ=φ 0 -2kπ k. determining the azimuth α of the transponder by performing the calculation: ##EQU23##

Claim 8

Dependent Claim 34 words

if the sign of Δφ is positive, φ=φ 0 +2kπ 2. if the sign of Δφ is negative, φ=φ 0 -2kπ k. determining the azimuth α of the transponder by performing the calculation: ##EQU23##

Claim 9

Dependent Claim 64 words

A method as in claim 1 where steps e-k are repeated for a plurality of successive time intervals at times t i occurring between t 1 and t 2 at a plurality of respective frequencies F i effecting the calculation of a plurality of azimuth values α i and where the azimuth α is determined by calculating the mean value of α i .

Claim 10

Independent Claim 168 words

An apparatus for measuring the azimuth of a radio wave transponder relative to a radar system, comprising: a. transmitting means for transmitting from the radar system to the transponder a signal having a frequency which varies linearly with time; b. means for returning from the transponder a signal representative of the transmitted signal; c. first and second receiving antennas located at a distance d from each other for receiving the returned signal at times which differ in relation to any differences in the distances between said receiving antennas and the transponder; d. first means for mixing the signal received at the first receiving antenna with the transmitted signal and for producing a first beat signal Fb 1 having a frequency fb 1 ; e. second means for mixing the signal received at the second receiving antenna with the transmitted signal and for producing a second beat signal Fb 2 having a frequency of fb 2 ; f. means for measuring phase shifts φ 0 and φ' 0 including:

Claim 11

Independent Claim 168 words

An apparatus for measuring the azimuth of a radio wave transponder relative to a radar system, comprising: a. transmitting means for transmitting from the radar system to the transponder a signal having a frequency which varies linearly with time; b. means for returning from the transponder a signal representative of the transmitted signal; c. first and second receiving antennas located at a distance d from each other for receiving the returned signal at times which differ in relation to any differences in the distances between said receiving antennas and the transponder; d. first means for mixing the signal received at the first receiving antenna with the transmitted signal and for producing a first beat signal Fb 1 having a frequency fb 1 ; e. second means for mixing the signal received at the second receiving antenna with the transmitted signal and for producing a second beat signal Fb 2 having a frequency of fb 2 ; f. means for measuring phase shifts φ 0 and φ' 0 including:

Claim 12

Dependent Claim 227 words

a first circuit coupled to the means for producing the first beat signal Fb 1 , said first circuit effecting production of a signal B 1 beginning with the first beat of Fb 1 following the transmission of a frequency F 1 at a time t 1 and ending upon completion of a predetermined number of beats of Fb 1 ; 2. a second circuit coupled to the means for producing the second beat signal Fb 2 , said second circuit effecting production of a signal B 2 beginning with the first beat of Fb 2 following the transmission of the frequency F 1 at time t 1 and ending upon completion of a predetermined number of beats of Fb 2 ; 3. means coupled to the first and second circuits for detecting the phase shift φ 0 between the beginnings of the signals B 1 , B 2 and for determining the phase shift φ' 0 between the endings of the signals B 1 , B 2 ; and g. computing means coupled to the phase shift measuring means and adapted for: 3. determining an overall phase variation Δφ by performing the calculation Δφ=φ' 0 -φ 0 ; 2. determining an approximate value φ.sub.Δφ for the phase shift between the signals Fb 1 and Fb 2 at the time t 1 by performing the calculation ##EQU24##

Claim 13

Dependent Claim 227 words

a first circuit coupled to the means for producing the first beat signal Fb 1 , said first circuit effecting production of a signal B 1 beginning with the first beat of Fb 1 following the transmission of a frequency F 1 at a time t 1 and ending upon completion of a predetermined number of beats of Fb 1 ; 2. a second circuit coupled to the means for producing the second beat signal Fb 2 , said second circuit effecting production of a signal B 2 beginning with the first beat of Fb 2 following the transmission of the frequency F 1 at time t 1 and ending upon completion of a predetermined number of beats of Fb 2 ; 3. means coupled to the first and second circuits for detecting the phase shift φ 0 between the beginnings of the signals B 1 , B 2 and for determining the phase shift φ' 0 between the endings of the signals B 1 , B 2 ; and g. computing means coupled to the phase shift measuring means and adapted for: 3. determining an overall phase variation Δφ by performing the calculation Δφ=φ' 0 -φ 0 ; 2. determining an approximate value φ.sub.Δφ for the phase shift between the signals Fb 1 and Fb 2 at the time t 1 by performing the calculation ##EQU24##

Claim 14

Dependent Claim 36 words

determining the value of a constant k to the nearest integer by performing the appropriate one of the following calculations: if the sign of Δφ is positive, ##EQU25## if the sign of Δφ is negative, ##EQU26##

Claim 15

Dependent Claim 36 words

determining the value of a constant k to the nearest integer by performing the appropriate one of the following calculations: if the sign of Δφ is positive, ##EQU25## if the sign of Δφ is negative, ##EQU26##

Claim 16

Dependent Claim 59 words

determining the accurate value of the phase shift φ between the signals Fb 1 and Fb 2 by performing the appropriate one of the following calculations: if the sign of Δφ is positive, φ=φ 0 +2kπ if the sign of Δφ is negative, φ=φ 0 -2kπ 5. determining the azimuth α of the transponder by performing the calculation ##EQU27##

Claim 17

Dependent Claim 59 words

determining the accurate value of the phase shift φ between the signals Fb 1 and Fb 2 by performing the appropriate one of the following calculations: if the sign of Δφ is positive, φ=φ 0 +2kπ if the sign of Δφ is negative, φ=φ 0 -2kπ 5. determining the azimuth α of the transponder by performing the calculation ##EQU27##

Claim 18

Dependent Claim 27 words

An apparatus as in claim 3 where the transmitting means comprises means for varying the frequency of the transmitted signal in response to a repetitive sawtooth waveform.

Claim 19

Dependent Claim 50 words

An apparatus as in claim 4 where said transmitting means includes a control loop for varying the period T of the sawtooth as a function of the distance between the radar system and the transponder, said variation being effected to maintain a predetermined one of the beat frequencies substantially constant.

Claim 20

Dependent Claim 26 words

An apparatus as in claim 4 or 5 where the transmitting means comprises means for producing the frequency F 1 at the beginning of each sawtooth.

Claim 21

Dependent Claim 281 words

An apparatus as in claim 3, 4 or 5 where said first and second circuits of the means for measuring the phase shifts φ 0 and φ 0 ' comprise: a. first and second shaping circuits for converting the beat signals Fb 1 and Fb 2 to representative square wave signals A 1 and A 2 , respectively; b. first and second synchronizing circuits having inputs coupled to the respective shaping circuits for receiving the signals A 1 and A 2 , each synchronizing circuit further having a start input, a stop input and an output, and producing a respective output signal B 1 , B 2 beginning with the first respective square wave signal A 1 , A 2 following receipt at its start input of a signal at time t 1 ; c. means for applying respective stop signals to the stop inputs of the synchronizing circuits after time t 2 to effect termination of the signals B 1 , B 2 when equal numbers of square wave pulses have been produced by the first and second shaping circuits; and further where said means coupled to said first and second circuits comprises: d. an exclusive-OR-gate having first and second inputs coupled to the outputs of the first and second synchronizing circuits for receiving the signals B 1 and B 2 and for successively producing at its output pulses of duration φ 0 and φ 0 '; e. counting means coupled to the output of the exclusive-OR-gate for measuring the durations φ 0 and φ 0 '; and f. a memory coupled to the output of the counting means for storing the values of φ 0 and φ 0 '.

Claim 22

Dependent Claim 180 words

An apparatus as in claim 7 where said means for producing the first and second stop signals comprise: a. first and second AND-gates having respective inputs for receiving the signals A 1 , B 1 and A 2 , B 2 ; b. first and second counters coupled to the outputs of the first and second AND-gates, respectively, for counting the numbers of pulses N 1 , N 2 produced thereby; c. a comparator coupled to the outputs of the first and second counters for producing a first signal when N 1 is greater than or equal to N 2 and for producing a second signal when N 2 is greater than or equal to N 1 ; and d. first and second AND-gates, each having a first input coupled to the comparator for receiving a respective one of the two signals produced thereby and having a second input for receiving a signal at time t 2 , and having respective outputs coupled to the stop inputs of the first and second sychronizing circuits for applying the respective stop signals.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1987-08-07	1988-02-06	1988-08-07	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1991-08-07	1992-02-06	1992-08-07	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1995-08-07	1996-02-06	1996-08-07	$7700.00	Window Closed / Lapsed

Determining azimuth of a transponder by measuring a plurality of phase shifts

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