# beamwidth2ap

Computes aperture length of unweighted antenna from beamwidth

## Syntax

``d = beamwidth2ap(hpbw,lambda)``
``d = beamwidth2ap(hpbw,lambda,azb)``

## Description

example

````d = beamwidth2ap(hpbw,lambda)` computes the aperture length `d` of an unweighted antenna from its half-power one-way beamwidth `hpbw`. `lambda` specifies the radar wavelength.```

example

````d = beamwidth2ap(hpbw,lambda,azb)` also specifies the azimuth impulse broadening factor `azb`.```

## Examples

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Compute the aperture length of a radar from its half-power beamwidth. The radar is designed to operate at a wavelength of 2 centimeters. The radar has a half-power beamwidth of one degree. Use the default azimuth broadening factor.

```lambda = 2e-2; bw = 1; aplen = beamwidth2ap(bw,lambda)```
```aplen = 1.1459 ```

Estimate the aperture lengths of two side-looking airborne radars operating at wavelengths of 1, 2, and 3 centimeters. The radars have beamwidths of 2 and 3 degrees in the azimuth dimension.

```lambda = [1,2,3]*1e-2; bw = [2,3]; aplen = beamwidth2ap(bw,lambda)```
```aplen = 2×3 0.2865 0.5730 0.8594 0.1910 0.3820 0.5730 ```

Compute the aperture length of a radar operating at a wavelength of 2 centimeters. The radar has a beamwidth of 2 deg in the azimuth direction. Use an azimuth broadening factor of 1.5.

```lambda = 2e-2; bw = 2; azbf = 1.5; ap = beamwidth2ap(bw,lambda,azbf)```
```ap = 0.8594 ```

Estimate the aperture length of each side of a rectangular aperture antenna. The antenna operates at a wavelength of 10 cm. In this case, the input beamwidth array `bw` describes the two beamwidths of the same antenna. The radar has a half-power beamwidth of 1 degree along one dimension and a half-power beamwidth of 2 degrees along the other.

```bw = [1,2]; lambda = 0.01; ap = beamwidth2ap(bw,lambda)```
```ap = 2×1 0.5730 0.2865 ```

## Input Arguments

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Half-power one-way beamwidth, specified as a positive scalar or as a J-by-K real-valued vector of positive values. Matrix rows correspond to the length of `d` and columns correspond to the length of `lambda`. Units are in degrees.

Radar wavelength, specified as a positive real scalar or a length-K vector of real values.

Example: `1.5`

Data Types: `double`

Azimuth impulse broadening factor, specified as a positive real scalar due to data weighting or windowing for side lobe control. The quantity is the actual –3 dB main lobe width with respect to the nominal width. Typical window functions such as `hamming` or `hann` exhibit azimuth impulse broadening factors in the range of 1 to 1.5.

Example: `1.2`

Data Types: `double`

## Output Arguments

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Length of unweighted antenna, returned as a positive scalar or length-J vector of positive values. Units are in meters.

Example: `[3.5,4.2]`

Data Types: `double`

## Algorithms

The half-power beamwidth (in degrees) for a rectangular aperture is 180λ/πd where λ is the radar wavelength and d is the aperture length. The azimuth broadening factor b multiplies the beamwidth to produce a half-power beamwidth of 180bλ/πd.

## Version History

Introduced in R2021b