# Documentation

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Package: phased

## Description

The RadarTarget System object™ models how a signal is reflected from a radar target. The quantity that determines the response of a target to an incoming signals is called the radar target cross-section (RCS). While all electromagnetic radar signals are polarized, you can sometimes ignore polarization and process them as if they were scalar signals. To ignore polarization, you should specify the EnablePolarization property as false. To utilize polarization, you must specify the EnablePolarization property as true. For non-polarized processing, the radar cross section is encapsulated in a single scalar quantity called the MeanRCS. For polarized processing, the radar cross-section is more generally expressed by a 2-by-2 scattering matrix in the ScatteringMatrix property. For both polarization processing types, there are several Swerling models available to be used to generate random fluctuations in the RCS. These models are chosen using the Model property. The random fluctuations are controlled by the SeedSource and Seed properties.

The properties that you can use to model the radar cross-section or scattering matrix depend upon the polarization type.

EnablePolarizationUse these properties
false
• MeanRCSSource

• MeanRCS

true
• ScatteringMatrixSource

• ScatteringMatrix

• Mode

To compute the signal reflected from a radar target:

2. Call step to compute the reflected signal according to the properties of phased.RadarTarget. 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.RadarTarget creates a radar target System object, H, that computes the reflected signal from a target.

H = phased.RadarTarget(Name,Value) creates a radar target object, H, with each specified property set to the specified value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

## Properties

EnablePolarization

Allow polarized signals

Set this property to true to allow the target to simulate the reflection of polarized radiation. Set this property to false to ignore polarization.

Default: false

Mode

Target scattering mode

Target scattering mode specified as one of 'Monostatic' or 'Bistatic'. If you set this property to 'Monostatic', the signal's reflection direction is the opposite to its incoming direction. If you set this property to 'Bistatic', the signal's reflection direction differs from its incoming direction. This property applies when you set the EnablePolarization property to true.

Default: 'Monostatic'

ScatteringMatrixSource

Source of target mean scattering matrix

Source of target mean scattering matrix specified as one of 'Property' or 'Input port'. If you set the ScatteringMatrixSource property to 'Property', the target's mean scattering matrix is determined by the value of the ScatteringMatrix property. If you set this property to 'Input port', the mean scattering matrix is determined by an input argument of the step method. This property applies only when you set the EnablePolarization property to true. When the EnablePolarization property is set to false, use the MeanRCSSource property instead, together with the MeanRCS property, if needed.

Default: 'Property'

ScatteringMatrix

Mean radar scattering matrix specified as a complex–valued 2-by-2 matrix. This matrix represents the mean value of the target's radar cross-section (in square meters). The matrix has the form [s_hh s_hv;s_vh s_vv]. In this matrix, the component s_hv specifies the complex scattering response when the input signal is vertically polarized and the reflected signal is horizontally polarized. The other components are defined similarly. This property applies when you set the ScatteringMatrixSource property to 'Property' and the EnablePolarization property to true. When the EnablePolarization property is set to false, use the MeanRCS property instead, together with the MeanRCSSource property. This property is tunable.

Default: [1 0;0 1]

MeanRCSSource

Source of mean radar cross section

Specify whether the target's mean RCS value(s) comes from the MeanRCS property of this object or from an input argument in step. Values of this property are:

 'Property' The MeanRCS property of this object specifies the mean RCS value(s). 'Input port' An input argument in each invocation of step specifies the mean RCS value.

When EnablePolarization property is set to true, use the ScatteringMatrixSource property together with ScatteringMatrix.

Default: 'Property'

MeanRCS

Specify the mean value of the target's radar cross section (in square meters) as a nonnegative scalar or as a 1-by-M nonnegative row vector. Using a vector allows you to process multiple targets simultaneous. The quantity Mis the number of targets. This property is used when MeanRCSSource is set to 'Property'. This property is tunable.

When EnablePolarization property is set to true, use the ScatteringMatrix property together with the ScatteringMatrixSource.

Default: 1

Model

Target statistical model

Specify the statistical model of the target as one of 'Nonfluctuating', 'Swerling1', 'Swerling2', 'Swerling3', or 'Swerling4'. If you set this property to a value other than 'Nonfluctuating', you must use the UPDATERCS input argument when invoking step. You can set the mean value of the radar cross-section model by specifying MeanRCS or use its default va;ue.

Default: 'Nonfluctuating'

PropagationSpeed

Signal propagation speed

Specify the propagation speed of the signal, in meters per second, as a positive scalar.

Default: Speed of light

OperatingFrequency

Signal carrier frequency

Specify the carrier frequency of the signal you are reflecting from the target, as a scalar in hertz.

Default: 3e8

SeedSource

Source of seed for random number generator

Specify how the object generates random numbers. Values of this property are:

 'Auto' The default MATLAB® random number generator produces the random numbers. Use 'Auto' if you are using this object with Parallel Computing Toolbox™ software. 'Property' The object uses its own private random number generator to produce random numbers. The Seed property of this object specifies the seed of the random number generator. Use 'Property' if you want repeatable results and are not using this object with Parallel Computing Toolbox software.

The random numbers are used to model random RCS values. This property applies when the Model property is 'Swerling1', 'Swerling2','Swerling3', or 'Swerling4'.

Default: 'Auto'

Seed

Seed for random number generator

Specify the seed for the random number generator as a scalar integer between 0 and 232–1. This property applies when you set the SeedSource property to 'Property'.

Default: 0

## Methods

 reset Reset states of radar target object step Reflect incoming signal
Common to All System Objects
clone

Create System object with same property values

getNumInputs

Expected number of inputs to a System object

getNumOutputs

Expected number of outputs of a System object

isLocked

Check locked states of a System object (logical)

release

Allow System object property value changes

## Examples

expand all

Create a simple signal and compute the value of the reflected signal from a target having a radar cross section of . Set the radar cross section using the MeanRCS property. Set the radar operating frequency to 600 MHz.

x = ones(10,1); sRadarTarget = phased.RadarTarget('Model','Nonfluctuating',... 'MeanRCS',10,... 'OperatingFrequency',600e6); y = step(sRadarTarget,x); disp(y(1:3)) 
 22.4355 22.4355 22.4355 

This value agrees with the formula where

 

## Algorithms

For a narrowband nonpolarized signal, the reflected signal, Y, is

$Y=\sqrt{G}\cdot X,$

where:

• X is the incoming signal.

• G is the target gain factor, a dimensionless quantity given by

$G=\frac{4\pi \sigma }{{\lambda }^{2}}.$
• σ is the mean radar cross-section (RCS) of the target.

• λ is the wavelength of the incoming signal.

The incident signal on the target is scaled by the square root of the gain factor.

For narrowband polarized waves, the single scalar signal, X, is replaced by a vector signal, (EH, EV), with horizontal and vertical components. The scattering matrix, S, replaces the scalar cross-section, σ. Through the scattering matrix, the incident horizontal and vertical polarized signals are converted into the reflected horizontal and vertical polarized signals.

$\left[\begin{array}{c}{E}_{H}^{\left(scat\right)}\\ {E}_{V}^{\left(scat\right)}\end{array}\right]=\sqrt{\frac{4\pi }{{\lambda }^{2}}}\left[\begin{array}{cc}{S}_{HH}& {S}_{VH}\\ {S}_{HV}& {S}_{VV}\end{array}\right]\left[\begin{array}{c}{E}_{H}^{\left(inc\right)}\\ {E}_{V}^{\left(inc\right)}\end{array}\right]=\sqrt{\frac{4\pi }{{\lambda }^{2}}}\left[S\right]\left[\begin{array}{c}{E}_{H}^{\left(inc\right)}\\ {E}_{V}^{\left(inc\right)}\end{array}\right]$

For further details, see Mott, [1] or Richards, [2] .

## References

[1] Mott, H., Antennas for Radar and Communications, John Wiley & Sons, 1992.

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

[3] Skolnik, M. Introduction to Radar Systems, 3rd Ed. New York: McGraw-Hill, 2001.