Research Of Multi-bands Antenna For Terminals

Antenna, as the device that couples energy between waveguide and free space, has been recognized as a critical element that can either enhance or constrain system performance in mobile communications. With the rapid development of personal wireless communication and internet access, multimedia services such as video and image are introduced into handheld terminals. Meanwhile, with the popularization of the third generation mobile communication technology in the global, more and more communication frequency bands are used. This imposes a technical problem on electromagnetics and antenna design: how to make the antenna not only small, conformal, but also multi-band, wide- band and versatile.In this thesis, a compact, low profile antenna used in handheld wireless communication terminal is proposed, which can receive communication signals from 3 bands including GSM, GPS and UMTS simultaneously.Based on the application background of the antenna, we designed several feasible system configurations: including a monopole antenna with meandered branch structure and another monopole antenna with long, straight and folded branch structure. They are in the size of 41mm×9.5mm×6.5mm, and both can cover the GSM, GPS and UMTS bands with their own advantages and disadvantages. According to the request of the design, the size of the antenna is reduced further and further. We make use of the different advantages of the two models above, and finally an antenna in the size of 40mm×6.5mm×3mm which can receive communication signals from 3 bands including GSM, GPS and UMTS at the same time is designed with some modification structures including adding a load, or adding a grounding line to change the antenna to a double PIFA structure. The bandwidth of the antenna is successfully broadened by adding an impedance matching network to the antenna. Especially in the GSM band, the absolute bandwidth can achieve about 100MHz which means the relative bandwidth is as wide as 11%. On the other hand, a plastic antenna base is added to make the antenna structure much firmer. And with the base, the performance of the antenna is largely improved by changing the position of the feeding point. Measured results show the radiation efficiency of the antenna can achieve -4dB level at all the GSM, GPS and UMTS bands. According to the problem we meet when the antenna is placed in the commercial phone model, the effect of the ground on the performance of the antenna is analyzed. Also, a kind of triple-band antenna with a slot in the ground is designed, which can solve the problem above successfully.