Efficiency Improvement Using Antenna Mode Cooperation for Foldable Smartphones

This paper presents a comprehensive study on the design and performance analysis of Inverted-F Antennas (IFAs) for foldable smartphones, with a particular focus on the impact of mode cooperation on antenna radiation efficiency. The basic structure consists of a driven IFA on the frame of the main screen, and a parasitic IFA on the frame of the auxiliary screen. The relationship between the two resonances provided by the two IFAs is analyzed. It is found that by setting the resonant frequency of driven IFA lower than that of the parasitic IFA, not only the impedance bandwidth is broadened, but also the radiation efficiency is greatly enhanced. The simulated −6 dB bandwidth is sufficient to cover the B5 (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$824-894 \text{MHz}$</tex>) band. Besides, the simulated average radiation efficiency in B 5 band is about −5 dB, which is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${2. 4\ \text{dB}}$</tex> higher than that of a single IFA.