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

step	Perform stretch processing for linear FM waveform

Common to All System Objects
release	Allow System object property value changes

Examples

Detect a Target Using Stretch Processing

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

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

Data Precision

This System object supports single and double precision for input data, properties, and arguments. If the input data X is single precision, the output data is single precision. If the input data X is double precision, the output data is double precision. The precision of the output is independent of the precision of the properties and other arguments.

References

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

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• See System Objects in MATLAB Code Generation (MATLAB Coder).

• This System object supports single and double precision for input data, properties, and arguments. If the input data X is single precision, the output data is single precision. If the input data X is double precision, the output data is double precision. The precision of the output is independent of the precision of the properties and other arguments.

Version History

Introduced in R2012a