What is the difference between ERP and EIRP

EIRP (Effective Isotropic Radiated Power) and ERP (Effective Radiated Power) are 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. Let us understand ERP and EIRP and derive difference between them.

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.

ERP (Effective Radiated Power)

• ERP is the amount of power radiated by an antenna compared to a half-wave dipole antenna.
• In ERP calculations, antenna gain is expressed in dBd (decibels relative to a half-wave dipole antenna).
• It indicates how effectively an RF system transmits energy in a specific direction.
• Higher ERP generally means larger coverage area and stronger received signal.

• The expression depicts ERP calculation formula, as mentioned ERP equals transmitter output power plus antenna gain relative to a dipole minus transmission line losses.

EIRP (Effective Isotropic Radiated Power)

• EIRP is the effective radiated power referenced to an isotropic antenna (ideal antenna radiating equally in all directions).
• Helps determine signal strength and communication range in RF system design.
• In EIRP calculations, antenna gain is expressed in dBi (decibels relative to an isotropic radiator).

• The expression depicts EIRP calculation formula, as mentioned EIRP equals transmitter power plus antenna gain relative to isotropic radiator minus cable/connector losses.

Relation between ERP and EIRP

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

Summary

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.