EEIRP vs EIRP vs ERP NTN Measurement:Key differences

In the evolution of 5G Advanced and the upcoming 6G standards; particularly with the integration of Non-Terrestrial Networks (NTN) and massive MIMO systems; measuring the radiated power of highly directional antennas is critical. This ensures that signals can close the link budget to a satellite or user equipment without causing unlawful interference to other systems.

To understand the radiated characteristics of these networks, engineers use three key metrics viz. EIRP, ERP and EEIRP. Here is an original explanation of each concept and the major differences between them.

EIRP (Effective Isotropic Radiated Power)

EIRP is the measured radiated power of a transmitter and its antenna in a single, specific direction, compared to a theoretical “isotropic” antenna. An isotropic antenna is an idealized point source that radiates power perfectly uniformly in all directions (a sphere).

When a 5G or 6G system uses beamforming, it concentrates the transmitter’s power into a narrow beam. EIRP tells you how much power a theoretical isotropic antenna would need to radiate to achieve the exact same signal strength in that specific target direction.

Following is the formula for EIRP calculation.

EIRP is the standard metric for Over The Air (OTA) output power testing. In NTN and mmWave (FR2) communications, EIRP is heavily used to calculate link budgets to satellites or distant receivers. It focuses on the peak direction of the beam.

Example (EIRP Calculation):

• TxP (Transmit Power) = +20 dBm
• L (Cable Loss) = -5 dB
• Gt (Antenna Gain) = +10 dBi

=> EIRP in dBm = +20 - 5 + 10 = 25 dBm

ERP (Effective Radiated Power)

ERP is almost identical in concept to EIRP, but instead of using a theoretical isotropic antenna as the baseline, it uses a standard half wave dipole antenna.

A half wave dipole is a real-world antenna that does not radiate equally in all directions; it naturally concentrates power in a donut shape, giving it an inherent gain of 2.15 dB over an isotropic radiator.

Following is the formula for ERP calculation.

While high-frequency 5G (mmWave) and NTN systems overwhelmingly use EIRP, regulatory bodies (like the FCC or ITU) often specify limits in ERP for sub-6 GHz terrestrial bands due to historical legacy. It is primarily used for regulatory compliance rather than advanced beamforming modeling.

Example (ERP Calculation):

Let’s say we have:

• TxP (Transmit Power) = +20 dBm
• L (Cable Loss) = -5 dB
• Gt (Antenna Gain) = +7.85 dBd

=> ERP = 22.85

EEIRP (Expected Equivalent Isotropic Radiated Power)

EEIRP is a newer, highly specialized metric used heavily in advanced 3GPP conformance testing (such as for Network Controlled Repeaters). Unlike EIRP, which measures power in one specific point/direction, EEIRP represents the spatially averaged power over a specific geometric region.

How EEIRP is measured

Advanced 5G and 6G arrays generate multiple dynamically steered beams. EEIRP calculates the expected interference or emission levels not just at the beam’s peak, but averaged over a “spherical strip” or angular sector. It requires a two-step averaging process:

1. Averaging the EIRP over various active test beam directions.
2. Averaging those results over a grid of horizontal (azimuth) and vertical (elevation) angles.

Following is the formula for EEIRP calculation.

$EEIRP = Integral/Average of EIRP(θ, φ) over spatial boundaries$

EEIRP is crucial for spatial emission testing. For example, when terrestrial 5G/6G systems operate near frequencies used by the Fixed Satellite Service (FSS), EEIRP is used to ensure that the aggregate, time averaged beamforming energy leaking into the sky does not blind orbiting satellites. It provides a realistic model of interference from dynamic beamsteering, rather than a worst case static peak.

Summary of key differences