Design of Low-SAR Terminal Antenna Using Characteristic Mode Manipulation

A novel specific absorption rate (SAR) reduction method based on the characteristic mode theory (CMT) is proposed for mobile terminal. The CMT is introduced to establish the relationship between the characteristic electric field and the induced electric field in human tissues. The design process and mechanism of a low-SAR antenna are demonstrated. To verify the effectiveness of the proposed SAR reduction method, a low-SAR loop antenna is designed. The measurement results show that the 10 g average SAR peak value of the proposed antenna is reduced by 26.1%. The measured −10 dB bandwidth of the low-SAR antenna is 320 MHz, which is increased by 60% compared with the reference antenna (200 MHz). The measured efficiency of the reference antenna and low-SAR antenna are better than 64% and 73% in the entire operating frequency band. With the advantages of bandwidth enhancement, significant SAR reduction and high antenna efficiency, the proposed SAR reduction method is a good choice for the low-SAR terminal antenna design.

I. Introduction

With the development of communication technology, various terminal devices have seen an explosive growth and have become part of human life. However, terminal devices typically operate near human tissues, which will lead to potential electromagnetic safety issues. To avoid excessive electromagnetic exposure, the industry proposes the specific absorption rate (SAR) to evaluate the magnitude of electromagnetic radiation received by human tissues, and stipulates the SAR safety limit of the antenna [1], [2].