Link Budgets and Propagation: Why Higher Frequencies Attenuate Faster

"Higher frequencies don't travel as far" is the standard explanation, but it hides the physics. This article shows where the numbers come from and how to use them when planning access point spacing.

Free-space path loss

The signal power lost between two antennas in free space is:

FSPL (dB) = 20 log10(d) + 20 log10(f) + 32.44

where d is distance in kilometres and f is frequency in MHz. Frequency enters through 20 log10(f), so loss rises with frequency regardless of distance.

Worked example: 10 metres (0.01 km)

The difference between 2.4 and 5 GHz at the same distance is about 6.4 dB, and between 2.4 and 6 GHz about 8 dB. Each 6 dB of extra loss roughly halves the free-space range for the same received signal.

Why frequency matters: antenna aperture

A common misunderstanding is that the atmosphere or space somehow absorbs higher frequencies more. In free space it does not. The real cause is that an antenna's effective area shrinks as wavelength gets shorter. With a fixed-gain antenna, a smaller aperture captures less of the power spreading out from the transmitter. If antenna aperture were held constant, for example with a larger antenna at the receiving end, the frequency penalty would disappear in free space. In Wi-Fi, device antennas are small and have similar gain across bands, so the frequency penalty applies in practice.

Materials add to the loss

Indoors, walls matter more than free-space loss. Typical approximate attenuation per obstruction rises with frequency:

These are indicative figures that vary widely with thickness and construction. Measure on site when it matters.

A simple link budget

A link budget adds gains and subtracts losses to estimate received power:

Received power = Transmit power + Transmit antenna gain + Receive antenna gain - Path loss - Other losses

Example at 5 GHz, 10 metres, one interior wall:

• Transmit power: 20 dBm
• Transmit antenna gain: 3 dBi
• Receive antenna gain: 0 dBi
• Path loss: 67 dB
• Wall: 4 dB
• Received power: 20 + 3 + 0 - 67 - 4 = about -48 dBm

Compare that with the receiver's needs. Higher data rates need stronger signals, and rough sensitivity values for 80 MHz channels in Wi-Fi 6 are around -70 dBm for mid-range rates and about -55 to -50 dBm for the highest. The gap between received power and the sensitivity for a given rate is the fade margin, which covers variations, people, and interference. Designers usually aim for 10 dB or more.

Real indoor environments

Walls, furniture, and reflections change the loss in ways simple formulas miss. Indoor models use a path-loss exponent greater than 2, often 3 to 4 in cluttered spaces, which makes distance matter far more than in free space.

Planning implications

• Spacing: access points on 5 and 6 GHz generally need to be closer together than on 2.4 GHz for the same coverage.
• Power balance: clients transmit at lower power than access points. Design to the weaker client link, not to the access point's strength.
• Walls: place access points so most users have clear or lightly obstructed paths.
• Bands in tandem: 2.4 GHz can provide a wide coverage floor, while 5 and 6 GHz provide capacity where users are.

See also Channel Widths Explained, since wider channels also raise the noise floor and reduce range.

Next Steps

Link budgets turn "the Wi-Fi is weak over there" into numbers you can act on. Our Networks & Infrastructure team plans access point spacing for Ugandan construction — concrete, brick, and metal all accounted for.

Request a Free Site Survey to get your building's propagation mapped properly.