# phased.ULA

Uniform linear array

## Description

`phased.ULA`

creates a uniform linear array (ULA)
System object™ and computes its response.

To compute the response for each element in the array for specified directions:

Create the

`phased.ULA`

object and set its properties.Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

## Creation

### Description

creates a uniform linear
`array`

= phased.ULA`array`

(ULA) System object. In this syntax, the object models a ULA formed with identical isotropic
phased array sensor elements. The origin of the local coordinate system is the phase
center of the array. The positive *x*-axis is the direction normal to the
array, and the elements of the array are located along the
*y*-axis.

creates the object `array`

= phased.ULA(`Name`

=`Value`

)`array`

with each specified property
`Name`

set to the specified `Value`

. You can
specify additional name-value pair arguments in any order as (`Name1`

=
`Value1`

, … ,`NameN`

=
`ValueN`

).

creates a ULA `array`

= phased.ULA(`N`

,`D`

,`Name`

=`Value`

)`array`

object with the `NumElements`

property set to `N`

, the `ElementSpacing`

property
set to `D`

, and other specified property Names set to the specified
Values. `N`

and `D`

are value-only arguments. When
specifying a value-only argument, specify all preceding value-only arguments. You can
specify name-value pair arguments in any order.

## Properties

Unless otherwise indicated, properties are *nontunable*, which means you cannot change their
values after calling the object. Objects lock when you call them, and the
`release`

function unlocks them.

If a property is *tunable*, you can change its value at
any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

`Element`

— phased array element

isotropic antenna element System object with default properties (default) | Phased Array System Toolbox™ antenna, microphone, or transducer element System object | Antenna Toolbox™ antenna System object

Phased array element, specified as a Phased Array System Toolbox antenna, microphone, or transducer element or Antenna Toolbox antenna.

**Example: **`phased.CosineAntennaElement`

`NumElements`

— Number of array elements

`2`

(default) | positive integer

Number of array elements, specified as a positive integer.

**Data Types: **`double`

`ElementSpacing`

— Array element spacing

`0.5`

(default) | positive scalar

Spacing between two adjacent elements in the array, specified as a positive scalar. Units are in meters.

**Data Types: **`double`

`ArrayAxis`

— Axis of linear array

`'y'`

(default) | `'x'`

`'z'`

Axis of linear array, specified as `'y'`

, `'x'`

, or
`'z'`

. Linear array elements are located along the selected
coordinate system axis. The array axis determines the direction along which the element
normal vectors point.

ArrayAxis Property Value | Element Normal Direction |
---|---|

`'x'` | azimuth = 90°, elevation = 0° (y-axis) |

`'y'` (default) | azimuth = 0°, elevation = 0° (x-axis) |

`'z'` | azimuth = 0°, elevation = 0° (x-axis) |

**Example: **`'z'`

**Data Types: **`char`

| `string`

`Taper`

— Array element tapers

`1`

(default) | complex-valued scalar | 1-by-*N* complex-valued row vector | *N*-by-1 complex-valued column vector

Array element tapering, specified as a complex-valued scalar,
1-by-*N* complex-valued row vector, or *N*-by-1
complex-valued column vector. *N* represents the number of elements of
the array. Tapers, also known as weights, are applied to each sensor element in the
sensor array and modify both the amplitude and phase of the received data. If
`'Taper'`

is a scalar, the same taper value is applied to all
elements. If `'Taper'`

is a vector, each taper value is applied to the
corresponding sensor element.

**Data Types: **`double`

## Usage

### Syntax

### Description

### Input Arguments

`freq`

— Array operating frequencies

length-*L* row vector of positive values

Array operating frequencies, specified as a length-*L* row
vector. Typical values are within the range specified by a frequency range property of
the array element. That property is called `FrequencyRange`

or
`FrequencyVector`

, depending on the type of array element. The
element has zero response at frequencies outside that range. Units are in Hz.

**Data Types: **`double`

`ang`

— Array response directions

length-*M* row vector with real values | 2-by-*M* matrix with real values

Array response directions, specified as a 2-by-*M* matrix or
length-*M* row vector.

If `ANG`

is a 2-by-*M* matrix, each column of
the matrix specifies the direction in the form ```
[azimuth;
elevation]
```

. The azimuth angle must lie between –180° and 180°, inclusive.
The elevation angle must lie between –90° and 90°, inclusive.

If `ang`

is a row vector of length *M*, each
element specifies the azimuth angle of the direction. In this case, the corresponding
elevation angle is assumed to be 0°.

Units are in degrees.

### Output Arguments

`resp`

— Voltage responses of phased array

*N*-by-*M*-by-*L*
complex-valued MATLAB^{®} array | MATLAB struct

Voltage responses of the phased array. The output depends on whether the array supports polarization or not.

If the array is not capable of supporting polarization, the voltage response,

`resp`

, has the dimensions*N*-by-*M*-by-*L*.*N*is the number of elements in the array. The dimension*M*is the number of angles specified in`ang`

.*L*is the number of frequencies specified in`freq`

. For any element, the columns of`resp`

contain the responses of the array elements for the corresponding direction specified in`ang`

. Each of the*L*pages of`resp`

contains the responses of the array elements for the corresponding frequency specified in`freq`

.If the array is capable of supporting polarization, the voltage response,

`resp`

, is a MATLAB`struct`

containing two fields,`resp.H`

and`resp.V`

. The field,`resp.H`

, represents the array’s horizontal polarization response, while`resp.V`

represents the array’s vertical polarization response. Each field has the dimensions*N*-by-*M*-by-*L*.*N*is the number of elements in the array, and*M*is the number of angles specified in`ang`

.*L*is the number of frequencies specified in`freq`

. Each column of`resp`

contains the responses of the array elements for the corresponding direction specified in`ang`

. Each of the*L*pages of`ang`

contains the responses of the array elements for the corresponding frequency specified in`freq`

.

## Object Functions

To use an object function, specify the
System object as the first input argument. For
example, to release system resources of a System object named `obj`

, use
this syntax:

release(obj)

### Specific to `phased.ULA`

and other array System objects

`beamwidth` | Compute and display beamwidth of an array |

`collectPlaneWave` | Simulate received plane waves at array |

`directivity` | Compute array directivity |

`getElementNormal` | Normal vectors for array elements |

`getElementPosition` | Positions of array elements |

`getNumElements` | Number of elements in an array |

`getTaper` | Array element tapers |

`isPolarizationCapable` | Array polarization capability |

`pattern` | Plot array directivity and patterns |

`patternAzimuth` | Plot array directivity or pattern versus azimuth |

`patternElevation` | Plot array directivity or pattern versus elevation |

`perturbations` | Perturbations defined on array |

`perturbedArray` | Apply perturbations to phased array |

`perturbedPattern` | Display pattern of perturbed array |

`plotGratingLobeDiagram` | Plot grating lobe diagram of array |

`thinnedArray` | Create thinned array from full array |

`viewArray` | View array geometry |

## Examples

### Directivity of Uniform Linear Array

Compute the directivities of two different uniform linear arrays (ULA). One array consists of isotropic antenna elements and the second array consists of cosine antenna elements. In addition, compute the directivity when the first array is steered in a specified direction. For each case, calculate the directivities for a set of seven different azimuth directions all at zero degrees elevation. Set the frequency to 300 MHz.

**Array of isotropic antenna elements**

First, create a 10-element ULA of isotropic antenna elements spaced 1/2-wavelength apart.

c = physconst('LightSpeed'); fc = 300e6; lambda = c/fc; ang = [-30,-20,-10,0,10,20,30; 0,0,0,0,0,0,0]; myAnt1 = phased.IsotropicAntennaElement; myArray1 = phased.ULA(10,lambda/2,'Element',myAnt1);

Compute the directivity.

`d = directivity(myArray1,fc,ang,'PropagationSpeed',c)`

`d = `*7×1*
-6.9886
-6.2283
-6.5176
10.0011
-6.5176
-6.2283
-6.9886

**Array of cosine antenna elements**

Next, create a 10-element ULA of cosine antenna elements spaced 1/2-wavelength apart.

myAnt2 = phased.CosineAntennaElement('CosinePower',[1.8,1.8]); myArray2 = phased.ULA(10,lambda/2,'Element',myAnt2);

Compute the directivity.

`d = directivity(myArray2,fc,ang,'PropagationSpeed',c)`

`d = `*7×1*
-1.9838
0.0529
0.4968
17.2548
0.4968
0.0529
-1.9838

The directivity of the cosine ULA is greater than the directivity of the isotropic ULA because of the larger directivity of the cosine antenna element.

**Steered array of isotropic antenna elements**

Finally, steer the isotropic antenna array to 30 degrees in azimuth and compute the directivity.

w = steervec(getElementPosition(myArray1)/lambda,[30;0]); d = directivity(myArray1,fc,ang,'PropagationSpeed',c,... 'Weights',w)

`d = `*7×1*
-297.2705
-13.9783
-9.5713
-6.9897
-4.5787
-2.0536
10.0000

The directivity is greatest in the steered direction.

### ULA Element Normals

Construct three ULAs with elements along the *x*-, *y*-, and *z*-axes. Obtain the element normals.

First, choose the array axis along the *x*-axis.

sULA1 = phased.ULA('NumElements',5,'ArrayAxis','x'); norm = getElementNormal(sULA1)

`norm = `*2×5*
90 90 90 90 90
0 0 0 0 0

The element normal vectors point along the *y*-axis.

Next, choose the array axis along the *y*-axis.

sULA2 = phased.ULA('NumElements',5,'ArrayAxis','y'); norm = getElementNormal(sULA2)

`norm = `*2×5*
0 0 0 0 0
0 0 0 0 0

The element normal vectors point along the *x*-axis.

Finally, set the array axis along the *z*-axis. Obtain the normal vectors of the odd-numbered elements.

sULA3 = phased.ULA('NumElements',5,'ArrayAxis','z'); norm = getElementNormal(sULA3,[1,3,5])

`norm = `*2×3*
0 0 0
0 0 0

The element normal vectors also point along the *x*-axis.

### ULA Element Positions

Construct a ULA with 5 elements along the z-axis. Obtain the element positions.

sULA = phased.ULA('NumElements',5,'ArrayAxis','z'); pos = getElementPosition(sULA)

`pos = `*3×5*
0 0 0 0 0
0 0 0 0 0
-1.0000 -0.5000 0 0.5000 1.0000

### Get Number of ULA Elements

Construct a default ULA and obtain the number of elements in that array.

array = phased.ULA; N = getNumElements(array)

N = 2

### Geometry and Indices of ULA Elements

Draw a 6-element ULA and use the `'ShowIndex'`

parameter to show the indices of the first and third elements.

array = phased.ULA(6); viewArray(array,'ShowIndex',[1 3],'ShowNormals',true, ... 'ShowLocalCoordinates',true,'Orientation',[60;100;45], ... 'ShowAnnotation',true)

### Construct ULA with Taylor Window

Construct a 5-element ULA with a Taylor window taper. Then, obtain the element taper values.

```
taper = taylorwin(5)';
array = phased.ULA(5,'Taper',taper);
w = getTaper(array)
```

`w = `*5×1*
0.5181
1.2029
1.5581
1.2029
0.5181

### Short-Dipole Antenna ULA Supports Polarization

Show that an array of `phased.ShortDipoleAntennaElement`

antenna elements supports polarization.

antenna = phased.ShortDipoleAntennaElement(... 'FrequencyRange',[1e9 10e9]); array = phased.ULA('NumElements',3,'Element',antenna); isPolarizationCapable(array)

`ans = `*logical*
1

The returned value of `1`

shows that this array supports polarization.

### Plot Pattern of 4-Element Antenna Array

Create a 4-element undersampled ULA and find the response of each element at boresight. Plot the array pattern at 1 GHz for azimuth angles between -180 and 180 degrees. The default element spacing is 0.5 meters.

```
array = phased.ULA('NumElements',4);
fc = 1e9;
ang = [0;0];
resp = array(fc,ang)
```

`resp = `*4×1*
1
1
1
1

c = physconst('LightSpeed'); pattern(array,fc,-180:180,0,'PropagationSpeed',c,... 'CoordinateSystem','rectangular',... 'Type','powerdb','Normalize',true)

### Plot Pattern of 10-Element Microphone ULA

Construct a 10-element uniform linear array of omnidirectional microphones spaced 3 cm apart. Then, plot the array pattern at 100 Hz.

mic = phased.OmnidirectionalMicrophoneElement(... 'FrequencyRange',[20 20e3]); Nele = 10; array = phased.ULA('NumElements',Nele,... 'ElementSpacing',3e-2,... 'Element',mic); fc = 100; ang = [0; 0]; resp = array(fc,ang); c = 340; pattern(array,fc,[-180:180],0,'PropagationSpeed',c,... 'CoordinateSystem','polar',... 'Type','powerdb',... 'Normalize',true);

### Plot Pattern of Array of Polarized Short-Dipole Antennas

Build a tapered uniform line array of 5 short-dipole sensor elements. Because short dipoles support polarization, the array should as well. Verify that it supports polarization by looking at the output of the `isPolarizationCapable`

method.

antenna = phased.ShortDipoleAntennaElement(... 'FrequencyRange',[100e6 1e9],'AxisDirection','Z'); array = phased.ULA('NumElements',5,'Element',antenna,... 'Taper',[.5,.7,1,.7,.5]); isPolarizationCapable(array)

`ans = `*logical*
1

Then, draw the array using the `viewArray`

method.

viewArray(array,'ShowTaper',true,'ShowIndex','All')

Compute the horizontal and vertical responses.

fc = 150e6; ang = [10]; resp = array(fc,ang);

Display the horizontal polarization response.

resp.H

`ans = `*5×1*
0
0
0
0
0

Display the vertical polarization response.

resp.V

`ans = `*5×1*
-0.6124
-0.8573
-1.2247
-0.8573
-0.6124

Plot an azimuth cut of the vertical polarization response.

c = physconst('LightSpeed'); pattern(array,fc,[-180:180],0,... 'PropagationSpeed',c,... 'CoordinateSystem','polar',... 'Polarization','V',... 'Type','powerdb',... 'Normalize',true)

### Plot Pattern of 9-Element ULA Antenna Array of Short Dipoles

Create an 9-element ULA of short dipole antenna elements spaced 1.5 meters apart. Display the azimuth and elevation directivities. The operating frequency is 500 MHz. Plot the directivities in polar coordinates.

Evaluate the fields at 45 degrees azimuth and 0 degrees elevation.

element = phased.ShortDipoleAntennaElement(... 'FrequencyRange',[50e6,1000e6],... 'AxisDirection','Z'); array = phased.ULA('NumElements',9,'ElementSpacing',1.5,'Element',element); fc = 500e6; ang = [45;0]; resp = array(fc,ang); disp(resp.V)

-1.2247 -1.2247 -1.2247 -1.2247 -1.2247 -1.2247 -1.2247 -1.2247 -1.2247

Display the azimuth directivity pattern at 500 MHz for azimuth angles between -180 and 180 degrees.

c = physconst('LightSpeed'); pattern(array,fc,[-180:180],0,... 'Type','directivity',... 'PropagationSpeed',c)

Display the elevation directivity pattern at 500 MHz for elevation angles between -90 and 90 degrees.

pattern(array,fc,[0],[-90:90],... 'Type','directivity',... 'PropagationSpeed',c)

### Plot Pattern of 10-Element ULA Antenna Array in UV Space

Create a 10-element ULA antenna array consisting of cosine antenna elements spaced 10 cm apart. Display the 3-D power pattern in UV space. The operating frequency is 500 MHz.

sCos = phased.CosineAntennaElement('FrequencyRange',[100e6 1e9],... 'CosinePower',[2.5,2.5]); sULA = phased.ULA('NumElements',10,... 'ElementSpacing',.1,... 'Element',sCos); c = physconst('LightSpeed'); fc = 500e6; pattern(sULA,fc,[-1:.01:1],[-1:.01:1],... 'CoordinateSystem','uv',... 'Type','powerdb',... 'PropagationSpeed',c)

### Plot Azimuth Pattern of ULA

Create a 7-element ULA of short-dipole antenna elements spaced 10 cm apart. Plot an azimuth cut of directivity at 0 and 10 degrees elevation. Assume the operating frequency is 500 MHz.

fc = 500e6; sCDant = phased.ShortDipoleAntennaElement('FrequencyRange',[100,900]*1e6); sULA = phased.ULA('NumElements',7,'ElementSpacing',0.1,'Element',sCDant); patternAzimuth(sULA,fc,[0 30])

You can plot a smaller range of azimuth angles by setting the `Azimuth`

property.

`patternAzimuth(sULA,fc,[0 30],'Azimuth',[-90:90])`

### Plot Elevation Pattern of ULA

Create a 6-element ULA of short-dipole antenna elements with element spacing of 10 cm. Plot an elevation cut of directivity at 0 and 90 degrees azimuth. Assume the operating frequency is 500 MHz.

fc = 500e6; c = physconst('LightSpeed'); elem = phased.ShortDipoleAntennaElement('FrequencyRange',[100,900]*1e6); array= phased.ULA('NumElements',6,'ElementSpacing',0.1,'Element',elem); patternElevation(array,fc,[0 90],'PropagationSpeed',c) legend('Location','southwest')

You can plot a smaller range of elevation angles by setting the `Elevation`

property to [0:90] degrees but now with cuts at 0 and 45 degrees azimuth.

patternElevation(array,fc,[0 45],'Elevation',[0:90],'PropagationSpeed',c) legend('Location','southwest')

### Plot Beamwidth of Sonar Array

Plot the beamwidth of a sonar array operating at a frequency of 2 kHz when the propagation speed of sound in water is 1500 m/s.

The sonar array consists of a 20-element uniform linear array (ULA). Consider the element of the ULA to be a backbaffled `phased.IsotropicProjector`

with a `VoltageResponse`

of 100 Volts and with a `FrequencyRange`

from 10 Hz to 300 kHz. Create a `phased.ULA`

object to model the uniform linear array.

projector = phased.IsotropicProjector('BackBaffled',true,... 'VoltageResponse',100,'FrequencyRange',[10 300000])

projector = phased.IsotropicProjector with properties: VoltageResponse: 100 FrequencyRange: [10 300000] BackBaffled: true

myArray = phased.ULA('Element',projector,'NumElements',20,... 'ElementSpacing',1500/200e3/2)

myArray = phased.ULA with properties: Element: [1x1 phased.IsotropicProjector] NumElements: 20 ElementSpacing: 0.0037 ArrayAxis: 'y' Taper: 1

Using the `beamwidth`

function, calculate and plot the 6 dB beamwidth of the sonar array.

beamwidth(myArray,200e3,'dBDown',6,'PropagationSpeed',1500)

ans = 6.9200

### Calculate Beamwidth and Angles of Uniform Linear Array (ULA)

Calculate the half-power beamwidth and angles of a 20-element uniform linear array (ULA) of cosine antenna elements.

Create a `phased.CosineAntennaElement`

object with the `'CosinePower'`

exponents set to 1.5.

myAnt = phased.CosineAntennaElement

myAnt = phased.CosineAntennaElement with properties: FrequencyRange: [0 1.0000e+20] CosinePower: [1.5000 1.5000]

Create a `phased.ULA`

object to model a 20-element ULA of cosine antenna elements. These elements are spaced at 0.5 meters on the azimuth plane.

array = phased.ULA('Element',myAnt,'NumElements',20)

array = phased.ULA with properties: Element: [1x1 phased.CosineAntennaElement] NumElements: 20 ElementSpacing: 0.5000 ArrayAxis: 'y' Taper: 1

Compute the beamwidth and angles of the array when it is operating at 3e8 Hz. Specify the beamwidth to be computed along the elevation plane.

[BW,Ang] = beamwidth(array,3e8,'Cut','Elevation')

BW = 74.8200

`Ang = `*1×2*
-37.4100 37.4100

### Response of Antenna ULA

Create a 4-element ULA of isotropic antenna elements and find the response of each element at boresight. Plot the array response at 1 GHz for azimuth angles between -180 and 180 degrees.

ha = phased.ULA('NumElements',4); fc = 1e9; ang = [0;0]; resp = step(ha,fc,ang); c = physconst('LightSpeed'); pattern(ha,fc,[-180:180],0,... 'PropagationSpeed',c,... 'CoordinateSystem','rectangular')

### Response of Microphone ULA Array

Find the response of a ULA array of 10 omnidirectional microphones spaced 1.5 meters apart. Set the frequency response of the microphone to the range 20 Hz to 20 kHz and choose the signal frequency to be 100 Hz. Using the `step`

method, determine the response of each element at boresight: 0 degrees azimuth and 0 degrees elevation.

mic = phased.OmnidirectionalMicrophoneElement( ... 'FrequencyRange',[20 20e3]); Nelem = 10; array = phased.ULA('NumElements',Nelem, ... 'ElementSpacing',1.5,'Element',mic); fc = 100; ang = [0;0]; resp = array(fc,ang)

`resp = `*10×1*
1
1
1
1
1
1
1
1
1
1

Plot the array directivity. Assume the speed of sound in air to be 340 m/s.

c = 340; pattern(array,fc,[-180:180],0,'PropagationSpeed',c,'CoordinateSystem','polar')

### Simulate Received Signals at ULA

Simulate two received plane-wave random signals at a 4-element ULA. The signals arrive from 10° and 30° azimuth. Both signals have an elevation angle of 0°. Assume the propagation speed is the speed of light and the carrier frequency of the signal is 100 MHz.

```
array = phased.ULA(4);
y = collectPlaneWave(array,randn(4,2),[10 30],100e6,physconst('LightSpeed'))
```

`y = `*4×4 complex*
0.7430 - 0.3705i 0.8433 - 0.1314i 0.8433 + 0.1314i 0.7430 + 0.3705i
0.8418 + 0.4308i 0.5632 + 0.1721i 0.5632 - 0.1721i 0.8418 - 0.4308i
-2.4817 + 0.9157i -2.6683 + 0.3175i -2.6683 - 0.3175i -2.4817 - 0.9157i
1.0724 - 0.4748i 1.1895 - 0.1671i 1.1895 + 0.1671i 1.0724 + 0.4748i

### Create Grating Lobe Diagram for ULA

Plot the grating lobe diagram for a 4-element uniform linear array having element spacing less than one-half wavelength. Grating lobes are plotted in u-v coordinates.

Assume the operating frequency of the array is 3 GHz and the spacing between elements is 0.45 of the wavelength. All elements are isotropic antenna elements. Steer the array in the direction 45 degrees in azimuth and 0 degrees in elevation.

c = physconst('LightSpeed'); f = 3e9; lambda = c/f; sIso = phased.IsotropicAntennaElement; sULA = phased.ULA('Element',sIso,'NumElements',4,... 'ElementSpacing',0.45*lambda); plotGratingLobeDiagram(sULA,f,[45;0],c);

The main lobe of the array is indicated by a filled black circle. The grating lobes in the visible and nonvisible regions are indicated by empty black circles. The visible region is defined by the direction cosine limits between [-1,1] and is marked by the two vertical black lines. Because the array spacing is less than one-half wavelength, there are no grating lobes in the visible region of space. There are an infinite number of grating lobes in the nonvisible regions, but only those in the range [-3,3] are shown.

The grating-lobe free region, shown in green, is the range of directions of the main lobe for which there are no grating lobes in the visible region. In this case, it coincides with the visible region.

The white area of the diagram indicates a region where no grating lobes are possible.

### Create Grating Lobe Diagram for Undersampled ULA

Plot the grating lobe diagram for a 4-element uniform linear array having element spacing greater than one-half wavelength. Grating lobes are plotted in u-v coordinates.

Assume the operating frequency of the array is 3 GHz and the spacing between elements is 0.65 of a wavelength. All elements are isotropic antenna elements. Steer the array in the direction 45 degrees in azimuth and 0 degrees in elevation.

c = physconst('LightSpeed'); f = 3e9; lambda = c/f; sIso = phased.IsotropicAntennaElement; sULA = phased.ULA('Element',sIso,'NumElements',4,'ElementSpacing',0.65*lambda); plotGratingLobeDiagram(sULA,f,[45;0],c);

The main lobe of the array is indicated by a filled black circle. The grating lobes in the visible and nonvisible regions are indicated by empty black circles. The visible region, marked by the two black vertical lines, corresponds to arrival angles between -90 and 90 degrees. The visible region is defined by the direction cosine limits $$-1\le u\le 1$$. Because the array spacing is greater than one-half wavelength, there is now a grating lobe in the visible region of space. There are an infinite number of grating lobes in the nonvisible regions, but only those for which $$-3\le u\le 3$$ are shown.

The grating-lobe free region, shown in green, is the range of directions of the main lobe for which there are no grating lobes in the visible region. In this case, it lies inside the visible region.

### Create Grating Lobe Diagram for ULA With Different Phase-Shifter Frequency

Plot the grating lobe diagram for a 4-element uniform linear array having element spacing greater than one-half wavelength. Apply a phase-shifter frequency that differs from the signal frequency. Grating lobes are plotted in u-v coordinates.

Assume the signal frequency is 3 GHz and the spacing between elements is 0.65 $$\lambda $$. All elements are isotropic antenna elements. The phase-shifter frequency is set to 3.5 GHz. Steer the array in the direction $$4{5}^{\circ}$$ azimuth, $${0}^{\circ}$$ elevation.

c = physconst('LightSpeed'); f = 3e9; f0 = 3.5e9; lambda = c/f; sIso = phased.IsotropicAntennaElement; sULA = phased.ULA('Element',sIso,'NumElements',4,... 'ElementSpacing',0.65*lambda ); plotGratingLobeDiagram(sULA,f,[45;0],c,f0);

As a result of adding the shifted frequency, the mainlobe shifts right towards larger $$u$$ values. The beam no longer points toward the actual source arrival angle.

The mainlobe of the array is indicated by a filled black circle. The grating lobes in the visible and nonvisible regions are indicated by empty black circles. The visible region, marked by the two black vertical lines, corresponds to arrival angles between $${\text{-}\text{90}}^{\circ}$$ and $${\text{90}}^{\circ}$$. The visible region is defined by the direction cosine limits $$-1\le u\le 1$$. Because the array spacing is greater than one-half wavelength, there is now a grating lobe in the visible region of space. There are an infinite number of grating lobes in the nonvisible regions, but only those for which $$-3\le u\le 3$$ are shown.

The grating-lobe free region, shown in green, is the range of directions of the main lobe for which there are no grating lobes in the visible region. In this case, it lies inside the visible region.

## References

[1] Brookner, E., ed. *Radar
Technology*. Lexington, MA: LexBook, 1996.

[2] Van Trees, H. *Optimum
Array Processing*. New York: Wiley-Interscience, 2002.

## Extended Capabilities

### C/C++ Code Generation

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

Usage notes and limitations:

`pattern`

,`patternAzimuth`

,`patternElevation`

,`plotResponse`

, and`viewArray`

methods are not supported.See System Objects in MATLAB Code Generation (MATLAB Coder).

## Version History

**Introduced in R2011a**

## See Also

`phased.ReplicatedSubarray`

| `phased.PartitionedArray`

| `phased.ConformalArray`

| `phased.CosineAntennaElement`

| `phased.CustomAntennaElement`

| `phased.CrossedDipoleAntennaElement`

| `phased.IsotropicAntennaElement`

| `phased.ShortDipoleAntennaElement`

| `phased.URA`

| `phased.UCA`

| `phased.HeterogeneousULA`

| `phased.HeterogeneousURA`

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