EIRP vs. ERP: Key Differences Explained

Let’s break down the difference between EIRP (Effective Isotropic Radiated Power) and ERP (Effective Radiated Power), two important concepts when dealing with radio frequency transmissions. Both relate to the power a transmitter radiates, but they use different reference points for antenna gain.

Here’s a summary of the major and minor differences:

• EIRP stands for Effective Isotropic Radiated Power.
• ERP stands for Effective Radiated Power.

The crucial difference lies in how antenna gain is measured:

• In EIRP calculations, antenna gain is expressed in dBi (decibels relative to an isotropic radiator).
• In ERP calculations, antenna gain is expressed in dBd (decibels relative to a half-wave dipole antenna).

This leads to a simple conversion:

• EIRP (in dBm) can be found by adding 2.15 to the ERP value (in dBm). This is because a half-wave dipole has a gain of approximately 2.15 dBi.

EIRP and ERP are not just theoretical concepts. Regulatory bodies use them to set limits for radio frequency transmitting devices across a variety of wireless technologies:

• These limits apply to indoor and outdoor wireless technologies such as GSM, LTE, 4G, 5G, LoRaWAN, and more.

To illustrate, here are the formulas for calculating EIRP and ERP:

Finally, a visual comparison:

In essence, both EIRP and ERP represent the effective power radiated by a transmitter, but they use different reference antennas (isotropic and half-wave dipole, respectively) for their calculations. Understanding this difference is key for complying with regulatory limits and optimizing wireless system performance.