This tool provides the RF power at a specified distance from a source transmitter and frequency of operation. It can be used to study the effect of frequency on received RF power.

**Calculator**

Enter

- Transmit Power
**P**(select the appropriate units of Watt or dBm)_{t} - Frequency of operation
**f** - Distance
**d** - Transmit Antenna Gain
**G**_{Tx} - Receive Antenna Gain
**G**_{Rx}

The calculator will provide the free space path loss and the received signal power in Watt or dBm.

**Example Calculation**

For a frequency of 1000 MHz and source power of +30 dBm, the received signal power at a distance of 10 meters is -22.45 dBm.

The table below shows the RF power as a function of frequency for the same ten meter distance.

Frequency (GHz) | RF Power (dBm) |
---|---|

1 | -22.5 |

2 | -28.5 |

3 | -32 |

4 | -34.5 |

5 | -36.4 |

6 | -38 |

7 | -39.3 |

8 | -40.5 |

9 | -41.5 |

10 | -42.5 |

**Background**

As frequency increases, the wavelength decreases. With this, the effective aperture of an antenna used to transmit or receive a signal also decreases.

**A _{eff} = λ^{2}/4π**

The path loss equation is derived from the following equation which shows that the received signal strength at a fixed distance **d** decreases with decreasing wavelength or increasing frequency.

**Pr = (Pt*Gt*Gr*λ ^{2})*(1/(4π*d^{2}))**

Where:

- Pr is the power received,
- Pt is the power transmitted,
- Gt is the gain of the transmitting antenna,
- Gr is the gain of the receiving antenna,
- λ is the wavelength of the RF signal,
- d is the distance between the antennas.

It’s also well known that higher frequency signals (such as mmWave) tend to experience greater atmospheric attenuation and absorption, resulting in higher losses over distance.

**However the path loss equation does not account for these losses. **Only those due to antenna gain, wavelength (frequency) and distance.

**References**

- Antenna Aperture on Wikipedia