Low-SAR Back Cover Mobile Antenna

Abstract

A novel antenna design with a low specific absorption rate (SAR) is introduced. The antenna has a very low profile and it is designed to be placed on the back cover of a mobile device at around 2 GHz. The solution is based on nested loops which distribute the field over a large volume so that the maximum SAR value remains relatively low in the user's tissue. The proposed design also provides relatively good efficiency, considering the extremely low profile, and the close proximity of lossy human tissue and the phone's main body. The manufactured prototype exhibits almost 50 % lower maximum SAR than a patch antenna used as a reference.

Cell Phone Radiation Exposure Limits and Engineering Solutions

“…Most notably, SAR decreases by at least 12.5%/mm for very short distances as a cell phone is moved away [ 104 , 105 , 106 , 107 ]. Antenna designs and placements within the phone influence SAR, as antennas that radiate power over larger areas [ 108 ] or are remotely positioned [ 109 ] produce lower SARs.…”

SAR measurements for back cover mobile antennas

“…Therefore, we have studied different figure-of-merits in order to include exposure consideration to an optimization process of the antenna [12]. This approach is also tested for a practical implementation with measurements [13].…”

“…In addition to that, it would be favorable to implement a high-order multiple-input multiple-output (MIMO) system. In [13], we presented a sophisticated back cover antenna design that has both a smaller footprint and lower SAR than a rectangle patch antenna.…”

“…A simple structure of a radiating element would be beneficial, but it should not be obtained at the expense of a larger size. In addition, strong resonances of patch antennas cause high SAR peak value [13]. Therefore, in this paper, we study the use of non-resonant antennas, which are typical in modern mobile devices in the low band.…”

“…The effect and potential of the matching circuit to decrease the SAR value is analyzed. The prototype is manufactured and measurement results are analyzed and compared with the prototypes from [13].…”