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# fspl

Free space path loss

## Syntax

```L = fspl(R,lambda) ```

## Description

`L = fspl(R,lambda)` returns the free space path loss in decibels for a waveform with wavelength `lambda` propagated over a distance of `R` meters. The minimum value of `L` is zero, indicating no path loss.

## Input Arguments

 `R` real-valued 1-by-M or M-by-1 vector Propagation distance of signal. Units are in meters. `lambda` real-valued 1-by-N or N-by-1 vector The wavelength is the speed of propagation divided by the signal frequency. Wavelength units are meters.

## Output Arguments

 `L` Path loss in decibels. M-by-N nonnegative matrix. A value of zero signifies no path loss. When `lambda` is a scalar, `L` has the same dimensions as `R`.

## Examples

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Calculate the free-space path loss (in dB) of a 10 GHz radar signal over a distance of 10 km.

```fc = 10.0e9; lambda = physconst('LightSpeed')/fc; R = 10e3; L = fspl(R,lambda)```
```L = 132.4478 ```

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### Free Space Path Loss

The free-space path loss, L, in decibels is:

`$L=20{\mathrm{log}}_{10}\left(\frac{4\pi R}{\lambda }\right)$`

This formula assumes that the target is in the far-field of the transmitting element or array. In the near-field, the free-space path loss formula is not valid and can result in a loss smaller than 0 dB, equivalent to a signal gain. For this reason, the loss is set to 0 dB for range values R ≤ λ/4π.

## References

[1] Proakis, J. Digital Communications. New York: McGraw-Hill, 2001.