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phased.RangeResponse

Range response

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Description

Thephased.RangeResponseSystem object™ performs range filtering on fast-time (range) data, using either a matched filter or an FFT-based algorithm. The output is typically used as input to a detector. Matched filtering improves the SNR of pulsed waveforms. For continuous FM signals, FFT processing extracts the beat frequency of FMCW waveforms. Beat frequency is directly related to range.

The input to the range response object is a radar data cube. The organization of the data cube follows the Phased Array System Toolbox™ convention.

  • The first dimension of the cube represents the fast-time samples or ranges of the received signals.

  • The second dimension represents multiple spatial channels, such as different sensors or beams.

  • 第三个维度,repr标准时间ent pulses.

Range filtering operates along the fast-time dimension of the cube. Processing along the other dimensions is not performed. If the data contains only one channel or pulse, the data cube can contain fewer than three dimensions. Because this object performs no Doppler processing, you can use the object to process noncoherent radar pulses.

The output of the range response object is also a data cube with the same number of dimensions as the input. Its first dimension contains range-processed data but its length can differ from the first dimension of the input data cube.

To compute the range response:

  1. Define and set up yourphased.RangeResponseSystem object. SeeConstruction.

  2. Call thestepmethod to compute the range response using the properties you specify for thephased.RangeResponseSystem object.

Note

Instead of using thestepmethod to perform the operation defined by the System object, you can call the object with arguments, as if it were a function. For example,y = step(obj,x)andy = obj(x)perform equivalent operations.

Construction

response = phased.RangeResponsecreates a range response System object,response.

response = phased.RangeResponse(Name,Value)creates a System object,response, with each specified propertyNameset to the specifiedValue. You can specify additional name and value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

Properties

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Range processing method, specified as'Matched filter'or'FFT'.

  • 'Matched filter'— The object match-filters the incoming signal. This approach is commonly used for pulsed signals, where the matched filter is the time reverse of the transmitted signal.

  • 'FFT'— The object applies an FFT to the input signal. This approach is commonly used for chirped signals such as FMCW and linear FM pulsed signals.

Example:'Matched filter'

Data Types:char

Signal propagation speed, specified as a real-valued positive scalar. Units are in meters per second. The default propagation speed is the value returned byphysconst('LightSpeed').

Example:3e8

Data Types:single|double

Signal sample rate, specified as a positive real-valued scalar. Units are in hertz.

Example:1e6

Data Types:single|double

Linear FM sweep slope, specified as a scalar. The fast-time dimension of thesignalinput argument tostepmust correspond to sweeps having this slope.

Example:1.5e9

Dependencies

To enable this property, set theRangeMethodproperty to'FFT'.

Data Types:single|double

Option to enable dechirping of input signals, specified asfalseortrue. Set this property tofalseto indicate that the input signal is already dechirped and no dechirp operation is necessary. Set this property totruewhen the input signal requires dechirping.

Dependencies

To enable this property, set theRangeMethodproperty to'FFT'.

Data Types:logical

Decimation factor for dechirped signals, specified as a positive integer. The decimation algorithm uses a 30th-order FIR filter generated byfir1(30,1/D), whereDis the decimation factor. The default value of1implies no decimation.

When processing FMCW signals, decimating the dechirped signal is useful for reducing the load on A/D converters.

Dependencies

To enable this property, set theRangeMethodproperty to'FFT'and theDechirpInputproperty totrue.

Data Types:single|double

Source of the FFT length used for the range processing of dechirped signals, specified as'Auto'or'Property'.

  • 'Auto'— The FFT length equals the length of the fast-time dimension of the input data cube.

  • 'Property'— Specify the FFT length by using theRangeFFTLengthproperty.

Dependencies

To enable this property, set theRangeMethodproperty to'FFT'.

Data Types:char

FFT length used for range processing, specified as a positive integer.

Dependencies

To enable this property, set theRangeMethodproperty to'FFT'and theRangeFFTLengthSourceproperty to'Property'

Data Types:single|double

FFT weighting window for range processing, specified as'None','Hamming','Chebyshev','Hann','Kaiser','Taylor', or'Custom'.

If you set this property to'Taylor', the generated Taylor window has four nearly constant sidelobes next to the mainlobe.

Dependencies

To enable this property, set theRangeMethodproperty to'FFT'.

Data Types:char

Sidelobe attenuation for range processing, specified as a positive scalar. Attenuation applies to Kaiser, Chebyshev, or Taylor windows. Units are in dB.

Dependencies

To enable this property, set theRangeMethodproperty to'FFT'and theRangeWindowproperty to'Kaiser','Chebyshev', or'Taylor'.

Data Types:single|double

自定义窗口范围内处理,作为一个指定function handle or a cell array containing a function handle as its first entry. If you do not specify a window length, the object computes the window length and passes that into the function. If you specify a cell array, the remaining cells of the array can contain arguments to the function. If you use only the function handle without passing in arguments, all arguments take their default values.

If you write your own window function, the first argument must be the length of the window.

Note

Instead of using a cell array, you can pass in all arguments by constructing a handle to an anonymous function. For example, you can set the value ofCustomRangeWindowto@(n)taylorwin(n,nbar,sll), where you have previously set the values ofnbarandsll.

Example:{@taylor,5,-35}

Dependencies

To enable this property, set theRangeMethodproperty to'FFT'and theRangeWindowproperty to'Custom'.

Data Types:function_handle|cell

Set reference range at center of range grid, specified astrueorfalse. Setting this property totrueenables you to set the reference range at the center of the range grid. Setting this property tofalsesets the reference range to the beginning of the range grid.

Dependencies

To enable this property, set theRangeMethodto'FFT'.

Data Types:logical

Reference range of the range grid, specified as a nonnegative scalar.

  • If you set theRangeMethodproperty to'Matched filter', the reference range is set to the start of the range grid.

  • If you set theRangeMethodproperty to'FFT', the reference range is determined by theReferenceRangeCenteredproperty.

    • When you set theReferenceRangeCenteredproperty totrue, the reference range is set to the center of the range grid.

    • When you set theReferenceRangeCenteredproperty tofalse, the reference range is set to the start of the range grid.

    Units are in meters.

This property is tunable.

Example:1000.0

Data Types:single|double

The source of the maximum number of samples the input signal, specified as'Auto'or'Property'. When you set this property to'Auto', the object automatically allocates enough memory to buffer the first input signal. When you set this property to'Property', you specify the maximum number of samples in the input signal using theMaximumNumInputSamplesproperty. Any input signal longer than that value is truncated.

To use this object with variable-size input signals in a MATLAB®Function Block in Simulink®, set theMaximumNumInputSamplesSourceproperty to'Property'and set a value for theMaximumNumInputSamplesproperty.

Example:'Property'

Maximum number of samples in the input signal, specified as a positive integer. Any input signal longer than this value is truncated. The input signal is the first argument to thestepmethod. The number of samples is the number of rows in the input.

Example:2048

Dependencies

To enable this property, set theRangeMethodproperty to'Matched filter'and set theMaximumNumInputSamplesSourceproperty to'Property'.

Data Types:single|double

Methods

plotResponse Plot range response
step Range response
Common to All System Objects
release

Allow System object property value changes

Examples

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Open Live Script

Compute the radar range response of three targets by using thephased.RangeResponseSystem object™. The transmitter and receiver are collocated isotropic antenna elements forming a monostatic radar system. The transmitted signal is a linear FM waveform with a pulse repetition interval of 7.0 μs and a duty cycle of 2%. The operating frequency is 77 GHz and the sample rate is 150 MHz.

fs = 150e6; c = physconst('LightSpeed'); fc = 77e9; pri = 7e-6; prf = 1/pri;

Set up the scenario parameters. The radar transmitter and receiver are stationary and located at the origin. The targets are 500, 530, and 750 meters from the radars on thex-axis. The targets move along thex-axis at speeds of −60, 20, and 40 m/s. All three targets have a nonfluctuating radar cross-section (RCS) of 10 dB.

Create the target and radar platforms.

Numtgts = 3; tgtpos = zeros(Numtgts); tgtpos(1,:) = [500 530 750]; tgtvel = zeros(3,Numtgts); tgtvel(1,:) = [-60 20 40]; tgtrcs = db2pow(10)*[1 1 1]; tgtmotion = phased.Platform(tgtpos,tgtvel); target = phased.RadarTarget('PropagationSpeed',c,'OperatingFrequency',fc,...'MeanRCS',tgtrcs); radarpos = [0;0;0]; radarvel = [0;0;0]; radarmotion = phased.Platform(radarpos,radarvel);

Create the transmitter and receiver antennas.

txantenna = phased.IsotropicAntennaElement; rxantenna = clone(txantenna);

Set up the transmitter-end signal processing. Create an upsweep linear FM signal with a bandwidth of half the sample rate. Find the length of the pri in samples and then estimate the rms bandwidth and range resolution.

bw = fs/2; waveform = phased.LinearFMWaveform('SampleRate',fs,...'PRF',prf,'OutputFormat','Pulses','NumPulses',1,'SweepBandwidth',fs/2,...'DurationSpecification','Duty cycle','DutyCycle',0.02); sig = waveform(); Nr = length(sig); bwrms = bandwidth(waveform)/sqrt(12); rngrms = c/bwrms;

Set up the transmitter and radiator System object properties. The peak output power is 10 W and the transmitter gain is 36 dB.

peakpower = 10; txgain = 36.0; transmitter = phased.Transmitter(...'PeakPower',peakpower,...'Gain',txgain,...'InUseOutputPort',true); radiator = phased.Radiator(...'Sensor',txantenna,...'PropagationSpeed',c,...'OperatingFrequency',fc);

Create a free-space propagation channel in two-way propagation mode.

channel = phased.FreeSpace(...'SampleRate',fs,...'PropagationSpeed',c,...'OperatingFrequency',fc,...'TwoWayPropagation',true);

Set up the receiver-end processing. The receiver gain is 42 dB and noise figure is 10.

collector = phased.Collector(...'Sensor',rxantenna,...'PropagationSpeed',c,...'OperatingFrequency',fc); rxgain = 42.0; noisefig = 10; receiver = phased.ReceiverPreamp(...'SampleRate',fs,...'Gain',rxgain,...'NoiseFigure',noisefig);

循环128次脉冲建立数据立方体。对each step of the loop, move the target and propagate the signal. Then put the received signal into the data cube. The data cube contains the received signal per pulse. Ordinarily, a data cube has three dimensions, where last dimension corresponds to antennas or beams. Because only one sensor is used in this example, the cube has only two dimensions.

The processing steps are:

  1. Move the radar and targets.

  2. Transmit a waveform.

  3. Propagate the waveform signal to the target.

  4. Reflect the signal from the target.

  5. Propagate the waveform back to the radar. Two-way propagation mode enables you to combine the returned propagation with the outbound propagation.

  6. Receive the signal at the radar.

  7. Load the signal into the data cube.

Np = 128; cube = zeros(Nr,Np);forn = 1:Np [sensorpos,sensorvel] = radarmotion(pri); [tgtpos,tgtvel] = tgtmotion(pri); [tgtrng,tgtang] = rangeangle(tgtpos,sensorpos); sig = waveform(); [txsig,txstatus] = transmitter(sig); txsig = radiator(txsig,tgtang); txsig = channel(txsig,sensorpos,tgtpos,sensorvel,tgtvel); tgtsig = target(txsig); rxcol = collector(tgtsig,tgtang); rxsig = receiver(rxcol); cube(:,n) = rxsig;end

Display the image of the data cube containing signals per pulse.

imagesc([0:(Np-1)]*pri*1e6,[0:(Nr-1)]/fs*1e6,abs(cube)) xlabel('Slow Time {\mu}s') ylabel(“快{\μ}年代”)

Figure contains an axes. The axes contains an object of type image.

Create aphased.RangeResponseSystem object in matched filter mode. Then, display the range response image for the 128 pulses. The image shows range vertically and pulse number horizontally.

matchingcoeff = getMatchedFilter(waveform); ndop = 128; rangeresp = phased.RangeResponse('SampleRate',fs,'PropagationSpeed',c); [resp,rnggrid] = rangeresp(cube,matchingcoeff); imagesc([1:Np],rnggrid,abs(resp)) xlabel('Pulse') ylabel('Range (m)')

Figure contains an axes. The axes contains an object of type image.

Integrate 20 pulses noncoherently.

intpulse = pulsint(resp(:,1:20),'noncoherent'); plot(rnggrid,abs(intpulse)) xlabel('Range (m)') title('Noncoherent Integration of 20 Pulses')

Figure contains an axes. The axes with title Noncoherent Integration of 20 Pulses contains an object of type line.

Algorithms

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References

[1] Richards, M.Fundamentals of Radar Signal Processing, 2nd ed. McGraw-Hill Professional Engineering, 2014.

[2] Richards, M., J. Scheer, and W. Holm,Principles of Modern Radar: Basic Principles. SciTech Publishing, 2010.

Extended Capabilities

See Also

Functions

Objects

Topics

Introduced in R2017a

Phased Array System Toolbox Documentation

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