Description
BHHL is a precisely defined physical and computational model, or 'phantom', that simulates the electromagnetic interaction between a wireless device and a human user. It is part of a suite of standardized phantoms specified by 3GPP for conformance testing. The BHHL model specifically represents a scenario where a user holds a mobile device (like a smartphone) against their head with their left hand. The phantom consists of detailed geometric models of a human head (including features like the ear and cheek) and a simplified hand model, all filled with a tissue-equivalent liquid that mimics the dielectric properties (permittivity and conductivity) of human tissues at specific frequency bands. This allows for highly controlled laboratory measurements that correlate to real-world user exposure.
In testing procedures, the device under test (DUT) is positioned in a precise, repeatable orientation relative to the BHHL phantom within an anechoic chamber or similar controlled environment. For SAR testing, a robotic probe system scans the phantom's surface or interior to measure the electric field strength, which is then used to calculate the rate of RF energy absorption (SAR) in watts per kilogram. This ensures the device complies with international safety limits for human exposure to electromagnetic fields. For OTA performance testing, such as Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS), the BHHL phantom's presence significantly affects the device's antenna radiation pattern and efficiency. Measurements are taken with the device in this 'loaded' condition to evaluate its real-world radio performance, as the human body absorbs and scatters RF energy, degrading antenna performance compared to free-space conditions.
The technical specifications for the BHHL phantom, including its exact dimensions, shape, and the dielectric properties of the tissue-simulating liquid, are detailed in 3GPP specifications like TS 38.161 (for NR) and the 38.8xx series. These specifications ensure global harmonization in testing methodologies, allowing for consistent and comparable results across different test laboratories and device manufacturers. The use of BHHL and its counterpart models (like BHHR for the right side) is critical for certifying that devices meet both regulatory safety requirements and minimum performance standards before they are released to the market, ensuring user safety and reliable network connectivity.
Purpose & Motivation
The BHHL phantom was introduced to address the critical need for standardized, realistic, and repeatable testing of mobile devices for RF exposure safety and radiated performance. Prior to such standardization, testing methodologies could vary, leading to inconsistencies in SAR and OTA results between different labs and regions. This made global device certification complex and could potentially allow devices with suboptimal real-world performance or borderline compliance to reach the market. The human body is a significant factor in a device's RF characteristics; a phone's antenna performance is drastically different when held in the hand and against the head compared to when it is in free space. Therefore, testing in isolation does not reflect actual user experience.
The creation of BHHL and related phantoms within 3GPP Rel-17 was motivated by the evolution of mobile technology, particularly the deployment of 5G New Radio (NR) in new frequency bands (including FR1 and FR2/millimeter wave). These new technologies required updated testing methodologies to account for different propagation characteristics and beamforming behaviors. Standardizing a phantom like BHHL ensures that all stakeholders—manufacturers, test houses, and regulators—have a common reference for evaluating devices. It solves the problem of test result variability and provides a scientifically robust model that represents a common, conservative usage scenario (left-handed call position), which is essential for ensuring consumer protection regarding RF exposure and for guaranteeing that network performance metrics like data throughput and call reliability are evaluated under realistic conditions.
Key Features
- Standardized geometric model of a human head and left hand for consistent device positioning
- Defined tissue-equivalent dielectric properties for accurate simulation of RF absorption and scattering
- Enables Specific Absorption Rate (SAR) compliance testing for regulatory safety certification
- Facilitates Over-The-Air (OTA) performance testing (e.g., TRP, TIS) under realistic user conditions
- Critical for evaluating antenna performance degradation due to user proximity (body loss)
- Supports testing across multiple frequency bands, including those used for 5G NR
Evolution Across Releases
Introduced the BHHL phantom as a new standardized test model within the 3GPP specifications for NR device conformance testing. It defined the complete geometric and dielectric parameters for the 'Beside Head and Hand Left Side' scenario, establishing the baseline methodology for integrated SAR and OTA performance testing of 5G devices in a common user position. This provided the foundational framework for consistent safety and performance evaluation.
Enhanced the applicability and references for the BHHL model within the broader test specification framework. Updates likely included refinements to alignment with other standards bodies (like IEC/IEEE), clarifications on testing procedures for new use cases, and potentially extended support for more complex multi-antenna and beamforming evaluation scenarios introduced in later 5G-Advanced studies.
Further evolution involved maintaining and updating the BHHL specifications to keep pace with the expanding 5G ecosystem. This includes potential updates to address testing for new frequency range combinations, support for integrated sensing and communications (ISAC) device evaluation, and harmonization with global regulatory requirements that may have evolved since the model's initial introduction.
Defining Specifications
| Specification | Title |
|---|---|
| TS 38.161 | 3GPP TR 38.161 |
| TS 38.561 | 3GPP TR 38.561 |
| TS 38.870 | 3GPP TR 38.870 |