# Documentation

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# phased.ArrayGain System object

Sensor array gain

## Description

The `ArrayGain` object calculates the array gain for a sensor array. The array gain is defined as the signal to noise ratio (SNR) improvement between the array output and the individual channel input, assuming the noise is spatially white. It is related to the array response but is not the same.

To compute the SNR gain of the antenna for specified directions:

1. Define and set up your array gain calculator. See Construction.

2. Call `step` to estimate the gain according to the properties of `phased.ArrayGain`. 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.ArrayGain` creates an array gain System object, `H`. This object calculates the array gain of a 2-element uniform linear array for specified directions.

`H = phased.ArrayGain(Name,Value)` creates and array-gain object, `H`, with the specified property Name set to the specified Value. You can specify additional name-value pair arguments in any order as (`Name1`,`Value1`,...,`NameN`,`ValueN`).

## Properties

 `SensorArray` Sensor array Sensor array specified as an array System object belonging to the `phased` package. A sensor array can contain subarrays. Default: `phased.ULA` with default property values `PropagationSpeed` Signal propagation speed Specify the propagation speed of the signal, in meters per second, as a positive scalar. Default: Speed of light `WeightsInputPort` Add input to specify weights To specify weights, set this property to `true` and use the corresponding input argument when you invoke `step`. If you do not want to specify weights, set this property to `false`. Default: `false`

## Methods

 step Calculate array gain of sensor array
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

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Calculate the array gain for a 4-element uniform linear array (ULA) in the direction 30° azimuth and 20° elevation. The array operating frequency is 300 MHz.

```fc = 300e6; array = phased.ULA(4); gain = phased.ArrayGain('SensorArray',array); g = gain(fc,[30;20])```
```g = -17.1783 ```

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## References

[1] Guerci, J. R. Space-Time Adaptive Processing for Radar. Boston: Artech House, 2003.

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