How do I calculate the EIRP of a phased array from the per-element power and number of elements?
Array EIRP
The EIRP is the most important system-level parameter for a transmit phased array because it determines the signal strength at the receiver. The EIRP combines two effects of increasing the array size: (1) more total power (N × Pelement) and (2) higher gain (G ∝ N). Together, EIRP increases as N²: EIRP = N × Pelement × N × Gelement_area = N² × Pelement × Gelement_area. In dB: EIRP = Pelement + 20·log10(N) + Gelement_area. However, this assumes that Gelement already includes the element spacing factor; when Gelement is the standalone element gain: EIRP = Pelement + 10·log10(N) + Garray.
| Parameter | Low Gain | Medium Gain | High Gain |
|---|---|---|---|
| Gain Range | 2-6 dBi | 6-15 dBi | 15-45 dBi |
| Beamwidth | 60-360° | 15-60° | 1-15° |
| Typical Types | Dipole, monopole, patch | Yagi, helical, horn | Parabolic, array, Cassegrain |
| Bandwidth | Narrow to wide | Moderate | Narrow to moderate |
| Complexity | Low | Medium | High |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
How much EIRP do I need for 5G?
5G NR mmWave base station: 55-65 dBm EIRP for outdoor macro coverage (300-500m range). Indoor small cell: 35-45 dBm EIRP. 5G handset: 20-25 dBm EIRP. The EIRP requirement drives the number of elements and the per-element power.
Does EIRP change with scan angle?
Yes. EIRP at scan angle θ = broadside EIRP - scan loss (dB). For cos^1.5(θ) scan loss: at 60° scan, EIRP drops by about 4.5 dB. The system must be designed with sufficient broadside EIRP to maintain the link margin at the maximum scan angle.
What about receive sensitivity?
The receive equivalent of EIRP is G/T (gain-to-temperature ratio). For a phased array receiver: G/T improves by 10·log10(N) compared to a single element if the noise contributions are uncorrelated. Array receive gain: Grx = Gelement + 10·log10(N). Array noise temperature: approximately equal to the element noise temperature (dominant) plus sky noise.