US 4,539,565 A · FM/CW radar linearization network and method therefor

Abstract

An FM/CW radar linearization network provides target identification data discriminating a target from background reflections and/or false targets by compensating for random variations in the linearity of the frequency sweep of the radar transmitter in the processing of the radar receiver signal, the latter being characteristic of the range and physical size of the target. Linearization is achieved by sampling the transmitter signal, generating an error signal proportional to and indicative of any deviations in the frequency sweep of the transmitter from that for linear operation, and applying that error signal to correct the target data signal, thereby frequency normalizing the same for processing and utilization. A number of alternatives in respect of the development of an appropriate error signal and further alternatives in its use as the basis for data correction are disclosed, including sampling of the transmitter in respect of the phase angle over a predetermined period or the time for a predetermined number of cycles, in order to develop an error signal proportional to and indicative of any deviations in the frequency sweep of the transmitter from that were its operation linear; while data correction may be made in one of a number of alternative ways, including phase rotation of the raw target data input signal, time-shifting of the sampling rate of such data, or frequency mixing the raw target data with an error control signal. Representative networks and suitable methodologies to achieve linearization are disclosed herein.

Claims50

Dependent claims

An FM/CW radar linearization network compensating for random variations in the linearity of the frequency sweep of the radar transmitter in the processing of the radar receiver signal characteristic of the range and physical size of a target to provide target identification data discriminating said target from background reflections, said network comprising:

a. raw target data generating means for developing a target data signal containing frequency un-normalized target identification information, wherein the instantaneous frequency of said target data signal is characteristic of the range of a target and the amplitude of said target data signal is characteristic of the size of said target at that range;
b. transmitter characteristic data generating means for developing a sampling signal containing transmitter frequency sweep information;
c. error data generating means receiving said sampling signal for developing an error signal characteristic of any nonlinearity in the sweep of the transmitter frequency;
and,
d. linearization means receiving said raw target data signal and said error signal for frequency normalizing target identification information by compensation for any random variation in the linearity of the sweep of transmitter frequency.

2 more elements

a. first transmitter/receiver frequency comparator means for developing a first target data signal I(t), the instantaneous frequency of which is characteristic of the range of said target and the amplitude of which is characteristic of the size of said target at that range;
b. second transmitter/receiver frequency comparator means for developing a second target data signal Q(t) identical to said first target data signal rotated through a 90.degree. angle;
c. transmitter characteristic data generating means for developing a sampling signal characteristic of the transmitter sweep frequency;
d. phase counter means receiving said sampling signal for developing a measured phase signal representative of the phase of said transmitter frequency at preselected sampling times;
e. signal generating means for developing a comparison signal characteristic of the phase of a transmitter operating under linear frequency sweep conditions at said preselected times;
f. phase error comparator means receiving said measured phase signal and said comparison signal for developing a phase error signal characteristic of any phase error in said transmitter frequency sweep resulting from nonlinear operation thereof;
and,
g. phase angle rotation means receiving said first and second target data signals and said phase error signal for rotating said first and second target data signals, I(t) and Q(t), respectively, by an error angle represented by said phase error signal to yield frequency normalized target data signals I'(t) and Q'(t), respectively, in accordance with the relationships:
I'(t)=cos .phi.I(t)+sin .phi.Q(t),
Q'(t)=sin .phi.I(t)-cos .phi.Q(t).

7 more elements

In an FM/CW radar system, wherein a transmitter signal and a receiver signal are mixed to yield a target data signal having a frequency spectrum the instantaneous frequency of which is representative of the range of a target and the amplitude of which at said instantaneous frequency is representative of the size of said target at said range, wherein said system is subject to operation over a random nonlinear sweep of transmitter frequency, the improvement comprising a linearization network compensating for nonlinearity, said network comprising:

a. transmitter/receiver mixer means for developing a complex, two channel target data signal represented vectorially as (I(t).sub.n, Q(t).sub.n) for times t.sub.n, wherein the vector rotates at times t.sub.1, t.sub.2, t.sub.3 . . . at a constant angular rate under linear transmitter sweep frequency conditions;
b. phase error means receiving a sampling signal characteristic of the linearity of said transmitter sweep for developing a phase error signal proportional to any nonlinearity in sweep frequency at times t.sub.n ;
and,
c. phase rotation means receiving said target data signal and said phase error signal for rotating said vector by an amount proportional to any phase error to maintain said angular rate constant.

1 more element

a. transmitter/receiver mixer means for developing a raw target data signal;
b. transmitter characteristic data mixer means receiving said transmitter signal and a standard frequency signal for developing a transmitter characteristic signal representative of the transmitter sweep;
c. counter means receiving said transmitter characteristic signal for counting a predetermined number of cycles thereof and developing a measured time signal proportional to the time period of said predetermined number of cycles;
d. comparison signal means for developing a time comparison signal proportional to the time expected for said predetermined number of cycles were the transmitter frequency sweep linear;
e. comparator means receiving the measured and expected time signals and developing a time error signal proportional to the difference thereof;
f. phase converter means receiving said time error signal and a signal proportional to the instantaneous frequency expected for linear operation, for developing a phase error signal representative of any nonlinearity in the sweep of transmitter frequency;
g. converter means for converting said phase error signal to a sample interval control signal;
h. linearizing means receiving said raw target data signal and said sample interval control signal, wherein the latter adjusts the sampling time of said raw data signal by a time proportional to any error due to nonlinearity in said sweep, thereby normalizing said target data signal;
and,
i. processing means receiving the normalized target data signal for discriminating said normalized signal into a plurality of frequency bands, wherein the instantaneous frequency of each band is characteristic of the range of said target and the amplitude at said instantaneous frequency is characteristic of the size of said target at said range.

7 more elements

A method for compensating for random variations in the linearity of the sweep of transmitter frequency of an FM/CW radar system in the processing of the receiver signal characteristic of the range and physical size of a target and thereby linearizing said signal to provide target identification data discriminating said target from background reflections, said method comprising the steps of:

a. developing a raw target data signal containing frequency un-normalized target identification information, wherein the instantaneous frequency of said raw target data signal is characteristic of the range of a target and the amplitude of said raw target data signal is characteristic of the physical size of said target at that range;
b. sampling the transmitter signal and developing a sampling signal containing transmitter frequency sweep information;
c. generating an error signal in response to said sampling signal characteristic of any nonlinearity in the sweep of said transmitter frequency;
and,
d. linearizing said raw target data signal in response to said error signal to frequency normalize said target data signal by proportionate compensation for any random variation in the linearity of the frequency sweep of said transmitter.

2 more elements

A method for compensating for random variations in the linearity of the sweep of transmitter frequency of an FM/CW radar system in the processing of the receiver signal characteristic of range and physical size of a target and thereby linearizing said signal to provide target identification data discriminating said target from background reflections, said method comprising the steps of:

a. mixing the transmitter and receiver signals in a first mixer means to develop a first raw target data signal I(t);
b. mixing said transmitter and receiver signals in a second mixer means to develop a second raw target data signal Q(t) rotated from said first signal by 90.degree., and wherein the phase angle .phi. between vectors (I(t).sub.n, Q(t).sub.n) rotates in vector space I(t), Q(t);
c. applying said raw target data signals to a phase rotator;
d. mixing said transmitter signal with a standard reference frequency signal to develop a transmitter characteristic signal;
e. applying said transmitter characteristic signal to a phase detector means to develop a measured phase signal representative of the phase of said transmitter frequency over a predetermined time period;
f. comparing said measured phase signal with a generated phase signal characteristic of the phase of a transmitter operating under linear frequency sweep conditions over said predetermined period, to develop a phase error signal indicative of and proportional to any nonlinear operation of said transmitter;
g. applying said phase error signal to said phase rotator to rotate said data signals I(t), Q(t) to yield frequency-normalized data signals I'(t), Q'(t) in accordance with the relationships:
I'(t)=cos .phi.I(t)+sin .phi.Q(t),
Q'(t)=sin .phi.I(t)-cos .phi.Q(t);
and,
h. processing said frequency-normalized signals in a filter network for discriminating said signals into a plurality of frequency bands, wherein the frequency of each band is characteristic of the range of said target and the signal amplitude within each band is characteristic of the size of said target.

8 more elements

A method for compensation for random variations in the linearity of the sweep of transmitter frequency of an FM/CW radar system in the processing of the receiver signal characteristic of the range and physical size of a target and thereby linearizing said signal to provide target identification data discriminating said target from background reflections, said method comprising the steps of:

a. mixing transmitter and receiver signals in a mixer means to develop a raw target data signal;
b. applying said raw target data signal to a time-sampling converter means;
c. mixing said transmitter signal with a standard frequency signal to develop a transmitter characteristic signal;
d. counting a preselected number of cycles of said transmitter characteristic signal and measuring the time period therefor to develop a measured time signal;
e. comparing said measured time signal with a generated time signal characteristic of the time for the identical number of cycles for a transmitter operating under linear frequency sweep conditions, to develop a time error signal;
f. applying said error signal and said generated time signal as inputs to a phase converter means to generate a phase error signal;
g. converting said phase signal into a time-sampling signal;
h. applying said time-sampling signal to said time-sampling converter to alter the sampling time of said raw data signal to conform to that were the transmitter frequency swept linearly to yield a frequency-normalized target data signal;
and,
i. processing said frequency-normalized signal in a filter network for discriminating said signal into a plurality of frequency bands, wherein the frequency of each band is characteristic of the range of said target and the signal amplitude within each band is characteristic of the size of said target.

7 more elements

Dependencies are inferred from the claim text.

FM/CW radar linearization network and method therefor

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FM/CW radar linearization network and method therefor

Life of this patent

Abstract

Claims50