For active array antennas, EIRP and G/T are the two most critical system-level performance metrics. They fully define the core wireless capability of an active array: EIRP quantifies transmit radiation capability, while G/T characterizes receive system sensitivity.
Together, these two parameters determine the practical communication performance of active array systems in satellite communications, wireless links, and radar applications. For satellite communication terminals specifically, EIRP and G/T directly govern:
- System link budget margin
- Maximum achievable data rate
- Signal coverage range and beam coverage capability
- Satellite access stability and anti-interference performance
- Electronic beam-steering performance
- System transmit power design requirements
- Receive signal margin and link robustness
A core engineering principle distinguishes active arrays from traditional antennas: EIRP and G/T are never determined by antenna aperture alone. The final system performance arises from the coupling and coordination of the entire RF chain and system design, including antenna elements, T/R modules, T/R chips, power amplifiers (PA), low-noise amplifiers (LNA), beamforming algorithms, RF transmission loss, channel calibration, thermal design, scan angle characteristics and system noise temperature.
EIRP stands for Equivalent Isotropically Radiated Power. It defines the effective transmit capability of an antenna system by calculating the equivalent radiated power of an ideal isotropic antenna that produces the same peak power density in the target steering direction.
In dB logarithmic units (industry standard for RF system analysis), the basic EIRP formula is:
EIRP=P_tx+G_tx
Where P_tx is transmit power (dBm/dBW) and G_tx is antenna transmit gain (dBi).
Practical Example
If a system features 40 dBm transmit power and 30 dBi antenna gain:
EIRP=40dBm+30dBi=70dBm
Unlike traditional single-feed antennas, active arrays adopt a distributed multi-channel RF architecture. The total EIRP is generated by coherent superposition of hundreds or thousands of independent T/R channels rather than a single power source.
The complete system-level EIRP formula for active arrays accounts for total array power, array gain and system loss:
EIRP=P_array+G_array-L_system
Parameter definitions:
- P_array: Effective total RF power generated by all array channels
- G_array: Synthesized beamforming gain of the entire antenna array
- L_system: Total system RF loss (transmission, matching, component loss)
The precise calculation boundary depends on the system’s reference plane definition, which is uniformly specified in active array engineering design specifications.
Why Active Array EIRP Is Fundamentally Different
Conventional parabolic antennas rely on a single high-power RF chain to feed the entire aperture, with fixed power distribution and limited beam flexibility. Active arrays decentralize power amplification and phase/amplitude control to every independent channel, realizing fully configurable beam synthesis.
Active Array Distributed RF Architecture
Beamforming Controller → Multi-channel Distribution → Independent T/R Modules → Antenna Elements → Coherent Radiated Beam
The final EIRP is entirely dependent on the coherent combination of all independent RF channels, which is the core advantage and key design difficulty of active array systems.
Per-Channel Power Accumulation Principle
Assume an active array consists of N identical transmit channels with consistent single-channel output power P_ch.
In linear power units, the total array conducted power is:
P_total=N×P_ch
Converted to logarithmic dB units (engineering conventional calculation):
P_(total,dBm)=P_(ch,dBm)+10log_10(N)
Typical Engineering Case
For a 1024-channel large-scale active array:
10log_10(1024)≈30.1dB
A single-channel output of 1 W can provide 30.1 dBW of total conducted power for the array (excluding system loss and non-ideal factor attenuation).
The Critical Role of Coherent Combining
Simple power superposition cannot generate high array gain. All channels must achieve strict coherent superposition in the target beam direction through precise phase and amplitude weighting.
The ideal array factor equation defines beam superposition performance:
Beamforming weight parameters An (amplitude) and ϕn (phase) directly determine the beam combining effect, array gain and final EIRP level.
Array Gain, Aperture and Frequency Characteristics
Aperture Gain Fundamental Formula
As an aperture antenna, the active array’s theoretical gain follows the classic aperture radiation principle:
Parameter definitions:
- η: Aperture radiation efficiency
- A: Physical aperture area of the array
- λ: Operating electromagnetic wavelength
This formula reveals the essential relationship between antenna gain, frequency and aperture size, which is the theoretical basis for active array index demonstration.
Frequency Impact on Gain and EIRP
Wavelength is inversely proportional to frequency: λ=c/f. Substitution shows that antenna gain is positively correlated with the square of frequency under the same aperture size and efficiency conditions:
G∝f^2
Higher frequency bands (such as millimeter wave) can obtain higher gain and EIRP with the same array scale, which is one of the core reasons for the widespread application of high-frequency active arrays in 5G/6G and high-speed satellite communication.
Element Quantity and Gain Scaling
Under ideal design conditions, increasing the number of array elements expands the effective aperture area and significantly improves array gain: 64 elements → 256 elements → 1024 elements, with gain increasing sequentially.
In practical engineering scenarios, the actual gain is restricted by multiple factors: element radiation efficiency, element spacing layout, aperture shape, mutual coupling between units, RF loss and beam scan angle.
Scan Loss and Steering-Angle EIRP Degradation
The active array achieves maximum gain and peak EIRP at the boresight direction (0° scan angle). When the beam is electronically steered to off-boresight angles, the array gain decreases, and this attenuation effect is defined as scan loss.
G(θ)<G(0)
For satellite communication terminals working in dynamic tracking scenarios, only focusing on boresight EIRP is insufficient. The full-space performance index EIRP(θ,ϕ) must be evaluated to ensure link stability at different scan angles.
Common active array EIRP evaluation specifications cover multi-angle test points: 0°, 20°, 40°, 60° scan angles, corresponding to different levels of scan loss and effective radiation performance.
Channel Error, Mutual Coupling and EIRP Attenuation
Ideal beamforming requires strict consistency between actual channel phase and theoretical phase: ϕn=ϕ(desired,n).
Actual system phase error: ϕn=ϕ(desired,n)+Δϕ_n.
Phase errors destroy coherent superposition, reduce array synthesis gain, and directly lead to EIRP_actual<EIRP_ideal. This is the core reason why high-precision array calibration is indispensable for active arrays.
Channel amplitude deviation ΔA_n changes the array aperture amplitude distribution, which not only reduces system gain and EIRP, but also deteriorates beam shape and raises sidelobe levels, affecting system anti-interference performance.
There is inevitable electromagnetic mutual coupling between densely arranged array elements, which changes the active impedance of units, PA load characteristics, radiation efficiency and far-field pattern. Finally, EIRP becomes a coupled function of PA performance, antenna characteristics, coupling state and beamforming algorithm.
Mutual coupling correction is particularly critical for compact small-spacing high-density active arrays.
T/R Hardware Chain: Core Source of EIRP Performance
Active array EIRP is essentially determined by the full-chain performance of T/R hardware. Every link from chip, module to antenna unit restricts the final radiation capability.
The T/R module is the basic unit of distributed RF power. It integrates power amplifier (PA), phase shifter, amplitude attenuator, RF switch and control circuit. Its saturated output power, linearity and efficiency directly determine the single-channel radiation power ceiling.
Integrated T/R chips control multi-channel RF functions, and their core indicators include output power, gain range, phase adjustment range/resolution, attenuation range/resolution, power efficiency and signal linearity, which jointly determine the accuracy and power capacity of beamforming synthesis.
PA Device and SSPA Performance
Power amplifier (PA) is the core power source of each channel. Solid-state Power Amplifiers (SSPA) are widely used in active arrays, built into T/R modules or deployed in the rear beamforming network. Higher single-channel PA output power improves total array EIRP, but brings higher power consumption and thermal pressure.
EIRP, Power Efficiency and Thermal Engineering Constraints
DC Power and Thermal Dissipation Principle
High EIRP output relies on high RF power, which requires large DC power supply support. The conversion relationship is:
P_DC≈P_RF/η_PA
The DC power consumed except RF effective power is converted into heat:
P_heat≈P_DC-P_RF
Engineering logic: Higher EIRP → Higher RF power → Higher DC power consumption → Higher heat generation → Strict thermal management design requirements
PAE (Power Added Efficiency) Core Index
PAE is a key metric to evaluate power amplifier energy efficiency, defined as:
PAE=(P_out-P_in)/P_DC
Higher PAE means lower DC power consumption and less heat dissipation under the same RF output power. It is a crucial design indicator for portable satellite terminals, airborne arrays, vehicle-mounted terminals and space-constrained active array systems, directly restricting the lightweight and high-efficiency implementation of high-EIRP arrays.
Active array EIRP is not a simple antenna aperture index, but a comprehensive system performance parameter determined by distributed multi-channel power synthesis, beamforming accuracy, hardware device performance, scan characteristics and thermal design. Different from traditional passive antennas, the distributed architecture of active arrays makes channel consistency, coherent combining efficiency and multi-physical field coupling design the core of EIRP optimization.
In satellite communication and high-performance wireless link scenarios, accurate EIRP modeling and optimization at different scan angles is the key to ensuring stable link budget, high data rate and reliable satellite access.
