Array Element Loss

Description

Array Element Loss (LE) is a parameter defined within 3GPP specifications to characterize the non-ideal, real-world performance of antenna arrays used in advanced radio systems, particularly for Multiple-Input Multiple-Output (MIMO) and beamforming. In an ideal theoretical array, each radiating element is assumed to be identical and lossless. However, in practice, manufacturing tolerances, material imperfections, mutual coupling between elements, and feed network losses introduce variations. LE models the aggregate power loss at each element, which degrades the effective isotropic radiated power (EIRP) and reduces the array gain. This loss is distinct from the overall system loss and is specifically attributed to the antenna element and its immediate feed structure.

From an architectural and operational perspective, LE is integrated into the link budget calculations and performance requirements defined in specifications like 38.820 (for NR) and 43.050 (for RF system scenarios). When a base station (gNB in 5G NR or eNB in LTE) forms a beam, the signal is weighted and fed to each antenna element. The LE value for each element attenuates the signal before it is radiated. System designers and network planners must account for this loss to ensure that the transmitted power meets regulatory limits and provides the intended coverage. It also influences the calibration procedures for the antenna array, as mismatches in LE between elements can lead to beam pattern distortions and increased sidelobe levels.

The role of LE in the network is fundamentally tied to ensuring accurate performance prediction and standardization. By defining typical or maximum permissible LE values, 3GPP enables consistent equipment testing and benchmarking across different vendors. This ensures that real-world base station deployments deliver the promised gains in spectral efficiency and coverage that MIMO and beamforming technologies offer. In massive MIMO systems with dozens or hundreds of elements, the cumulative impact of LE can be significant, making its accurate characterization essential for predicting cell-edge throughput and overall network capacity.

Purpose & Motivation

The concept of Array Element Loss was introduced to bridge the gap between ideal antenna array theory and practical implementation within 3GPP standards. Early MIMO and smart antenna systems were often modeled with perfect elements, leading to optimistic performance predictions that did not match field deployment results. The purpose of defining LE is to inject realism into system specifications, ensuring that performance requirements and conformance tests reflect attainable hardware performance. This allows for fair comparison between different vendor equipment and sets realistic expectations for network operators.

Historically, as cellular systems evolved from single-antenna transceivers to complex multi-antenna systems in LTE (Rel-8 onwards) and particularly with the advent of large-scale beamforming in 5G NR, the need for detailed RF parameter modeling became critical. Without accounting for per-element losses, the calculated beamforming gain and signal-to-interference-plus-noise ratio (SINR) would be overstated. This could lead to under-dimensioned networks, coverage holes, and failure to meet quality of service targets. By standardizing LE, 3GPP addresses the limitations of previous simplistic models and provides a common framework for specifying and testing the radio frequency performance of antenna arrays.

Furthermore, LE is crucial for defining the conducted requirements for base station transceivers. Specifications separate the performance of the active radio unit from the passive antenna array. Defining LE allows for clear interface points (like the antenna connector) and ensures that the combined system—active and passive parts—meets the overall radiated performance standards. This modular approach facilitates a multi-vendor ecosystem where radio units and antennas can be sourced independently, provided they meet the individual LE and other parametric requirements.

Key Features

• Models per-antenna-element power loss in an array
• Critical for accurate MIMO and beamforming system performance prediction
• Integrated into 3GPP link budget and RF conformance testing specifications
• Distinct from overall system path loss or cable loss
• Impacts effective isotropic radiated power (EIRP) and array gain
• Essential for realistic simulation and network planning tools

Evolution Across Releases

Defining Specifications