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phased.StretchProcessor

Stretch processor for linear FM waveform

Description

The StretchProcessor object performs stretch processing on data from a linear FM waveform.

To perform stretch processing:

  1. Define and set up your stretch processor. See Construction.

  2. Call step to perform stretch processing on input data according to the properties of phased.StretchProcessor. The behavior of step is specific to each object in the toolbox.

Note

Starting in R2016b, instead of using the step method 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) and y = obj(x) perform equivalent operations.

Construction

H = phased.StretchProcessor creates a stretch processor System object, H. The object performs stretch processing on data from a linear FM waveform.

H = phased.StretchProcessor(Name,Value) creates a stretch processor object, H, with additional options specified by one or more Name,Value pair arguments. Name is a property name, and Value is the corresponding value. Name must appear inside single quotes (''). You can specify several name-value pair arguments in any order as Name1,Value1,…,NameN,ValueN.

Properties

SampleRate

Sample rate

Signal sample rate, specified as a positive scalar. Units are Hertz. The ratio of sample rate to pulse repetition frequency (PRF) must be a positive integer — each pulse must contain an integer number of samples. This property can be specified as single or double precision.

Default: 1e6

PulseWidth

Pulse width

Specify the length of each pulse (in seconds) as a positive scalar. The value must satisfy PulseWidth <= 1./PRF. This property can be specified as single or double precision.

Default: 50e-6

PRFSource

Source of pulse repetition values

Source of the PRF values for the stretch processor, specified as 'Property', 'Auto', or 'Input port'. When you set this property to 'Property', the PRF is determined by the value of the PRF property. When you set this property to 'Input port', the PRF is determined by an input argument to the step method at execution time. When you set this property to 'Auto', the PRF is computed from the number of rows in the input signal.

Default: 'Property'

PRF

Pulse repetition frequency

Pulse repetition frequency (PRF) of the received signal, specified as a positive scalar. Units are in Hertz. This property can be specified as single or double precision.

Dependencies

To enable this property, set the PRFSource property to 'Property'.

Default: 1

SweepSlope

FM sweep slope

Specify the slope of the linear FM sweeping, in hertz per second, as a scalar.

Default: 2e9

SweepInterval

Location of FM sweep interval

Specify the linear FM sweeping interval using the value 'Positive' or 'Symmetric'. If SweepInterval is 'Positive', the waveform sweeps in the interval between 0 and B, where B is the sweep bandwidth. If SweepInterval is 'Symmetric', the waveform sweeps in the interval between –B/2 and B/2. This property can be specified as single or double precision.

Default: 'Positive'

PropagationSpeed

Signal propagation speed

Specify the propagation speed of the signal, in meters per second, as a positive scalar. You can specify this property as single or double precision.

Default: Speed of light

ReferenceRange

Reference range of stretch processing

Specify the center of ranges of interest, in meters, as a positive scalar. The reference range must be within the unambiguous range of one pulse. This property can be specified as single or double precision. This property is tunable.

Default: 5000

RangeSpan

Span of ranges of interest

Specify the length of the interval for ranges of interest, in meters, as a positive scalar. The range span is centered at the range value specified in the ReferenceRange property. This property can be specified as single or double precision.

Default: 500

Methods

stepPerform stretch processing for linear FM waveform
Common to All System Objects
release

Allow System object property value changes

Examples

expand all

Use stretch processing to locate a target at a range of 4950 m.

Note: This example runs only in R2016b or later. If you are using an earlier release, replace each call to the function with the equivalent step syntax. For example, replace myObject(x) with step(myObject,x).

Simulate the signal.

waveform = phased.LinearFMWaveform;
x = waveform();
c = physconst('LightSpeed');
rng = 4950.0;
num_samples = round(rng/(c/(2*waveform.SampleRate)));
x = circshift(x,num_samples);

Perform stretch processing.

stretchproc = getStretchProcessor(waveform,5000,200,c);
y = stretchproc(x);

Plot the spectrum of the resulting signal.

[Pxx,F] = periodogram(y,[],2048,stretchproc.SampleRate,'centered');
plot(F/1000,10*log10(Pxx))
grid
xlabel('Frequency (kHz)')
ylabel('Power/Frequency (dB/Hz)')
title('Periodogram Power Spectrum Density Estimate')

Detect the range.

[~,rngidx] = findpeaks(pow2db(Pxx/max(Pxx)),'MinPeakHeight',-5);
rngfreq = F(rngidx);
rng = stretchfreq2rng(rngfreq,stretchproc.SweepSlope,stretchproc.ReferenceRange,c)
rng = 4.9634e+03

Algorithms

expand all

References

[1] Richards, M. A. Fundamentals of Radar Signal Processing. New York: McGraw-Hill, 2005.

Extended Capabilities

Introduced in R2012a