EMF Exposure in MIMO Antenna Systems
Holistic Evaluation, Mitigation Strategies, and FR2/FR3 Advancements
Time: Fri 2026-09-18 15.00
Location: F3, Lindstedtvägen 26
Video link: https://kth-se.zoom.us/j/69650632339
Language: English
Subject area: Electrical Engineering
Doctoral student: Wenfu Fu , Elektromagnetism och plasmafysik
Opponent: Professor Anja Skrivervik, EPFL, Lausanne, Switzerland
Supervisor: Professor Sailing He, Elektromagnetism och plasmafysik
QC 20260831
Abstract
With the rapid development of wireless communication systems driven by the demand for higher data rates and sufficient coverage, a factor that may limit communication performance is the compliance requirements for radio frequency (RF) electromagnetic field (EMF) exposure. This thesis presents a holistic study on the EMF exposure in modern antenna systems, facilitating improvements in RF device communication performance while fulfilling EMF exposure compliance. The thesis provides comprehensive studies from an evaluation process to the EMF solutions for sub-6 GHz indoor base stations, and early research for Frequency Range 2 (FR2) and FR3 RF equipment.
For sub-6 GHz indoor base stations (BSs), two main contributions are made. First, a holistic evaluation framework is established to assess power-related multiplexing efficiency, considering antenna radiation characteristics, indoor propagation scenarios, and the power reduction resulting from ensuring EMF compliance at any distance from the device (i.e. touch compliance). The proposed evaluation framework gives antenna designers a valuable basis for comparing and optimizing MIMO antenna systems while considering specific absorption rate (SAR) touch compliance and various deployment scenarios for indoor BSs. Second, passive and active EMF solutions are developed to achieve improved communication performance while ensuring EMF touch compliance. Regarding passive designs, two antenna are proposed, including a dedicated monopole antenna and a patch antenna. These designs spread the SAR distributions and thus lower the peak SAR levels, achieving touch compliance for indoor BSs without power reduction. In addition, a novel active EMF solution is proposed by reusing the communication antenna as a proximity sensor. By detecting human proximity through variations in the antenna's reflection coefficient, the BS can maintain high transmission power during normal operation and only trigger power back-off mechanisms when a human body enters the EMF exclusion zone.
As 6G systems can shift toward FR2 and FR3 bands, where the exposure metrics are absorbed power density (APD) and incident power density (IPD), three further contributions are made. First, a comprehensive review of state-of-the-art IPD and APD assessment methodologies is conducted. It aims to identify open challenges and potential future directions for accurate assessment of EMF exposure. Second, a novel metasurface-based conformal human phantom is proposed, with the potential to serve as a new test equipment for EMF assessment. Finally, an analysis of the implications of APD limits on 6G user equipment (UE) is conducted, establishing system design benchmarks, such as maximum allowed transmitted power and equivalent isotropically radiated power (EIRP) levels, for both single- and dual-antenna systems within the 6-15 GHz spectrum.
In conclusion, the contributions of this thesis provide a set of tools related to EMF exposure research. The work also helps the future FR2/3 device development and EMF assessment equipment.