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dBd Vs dbi-Difference between dBd and dBi

This page describes what is dBd and dBi and mentions relation between dBd and dBi units used for directional gain of antenna.

Antenna manufacturers usually use these units dBd and dBi to calculate the directional gain of the antennas. Following sections mention difference between dBd and dBi.

What is dBd

It is used in calculation of directional gain compared to dipole antenna. The last letter 'd' in the word 'dBd' denotes dipole.

What is dBi

It is used in calculation of directional gain compared to isotropic radiator. The last letter 'i' in the word 'dBi' denotes isotropic.

Both dBd and dBi are the values calculated against the input power to determine the directional output power of the antenna.

Relation between dBd and dBi

The dBd value is compared with a dipole antenna, which itself has 2.14 dB gain over isotropic radiator. With this logic, antenna having gain of 7dBd will have gain of 9.14 in units of dBi.

In other words both 7dBd and 9.14dBi with respect to antenna gain are equivalent.

Following formula mentions relation between dBd and dBi.

0 dBd = 2.14 dBi

Hence to convert dBd to dBi, just Add 2.14

To convert from dBi to dBd, just substract 2.14