| Summary: | 碩士 === 逢甲大學 === 通訊工程學系 === 104 === This study focuses on compact multiband antennas, which can be used in smart phones and tablet computers. There are three different types presented in this research. Basically, the main structures of these antennas are an inverted-L monopole, a multi-branch monopole, and using a matching circuit with SMD inductor and capacitor.
The first antenna can be applied in smart phones. It consists of an inverted-L feeding strip which is coupled to two folded shorting strips, one of them utilizing a three-dimensional bending structure. With this combination the design can not only reduce the antenna’s size but also reach the design requirements in lower band as well. As a result, this antenna only occupies 50×12×3 〖mm〗^3 and is fabricated on a 0.8 mm thick FR4 substrate, with a relative permittivity of 4.4 and a loss tangent 0.02. Its operating frequencies can cover LTE700/2300/2500 (704~787, 2300~2400, 2500~2690 MHz), GSM850/900 (824~894, 890~960 MHz), DCS (1710~1880 MHz), and WLAN2400 (2400~2488 MHz) bands.
The second one is a multiband antenna also for smart phone. It can provide multiband operations in LTE700/2300/2500 (704~787, 2300~2400, 2500~2690 MHz), DCS (1710~1880 MHz), PCS (1850~1990 MHz), UMTS2100 (1920~2170 MHz) and WLAN2400 (2400~2488 MHz) bands. The antenna is formed by a multi-branch monopole coupled to a folded shorting strip, which is designed into a stereoscopic structure. This arrangement can not only reduce its size but also enhance the bandwidth of lower bands. It has a size of 55×11×3 〖mm〗^3, and is fabricated on a FR4 substrate, with a thickness of 0.8 mm, a relative permittivity of 4.4 and a 0.02 loss tangent. Similarly, both the first and the second designs can be applied in the 3G and 4G smart phones to provide the voice and internet/Wi-Fi services.
The third one is a dual-wideband monopole antenna used in tablet computers for LTE operation. It is designed to cover operating frequencies of LTE700/900/2300/2500 (704 ~ 787, 885 ~ 960, 2300 ~ 2400, 2500 ~ 2690 MHz) and WLAN (2400 ~ 2488 MHz). By connecting a 9.1nH SMD chip inductor, it can decrease its required length. In addition, this antenna’s operating bands can be modified by adjusting the matching circuit’s SMD components to achieve the design requirement of lower band. Consequently, its advantages are simple structure, easy fabrication, small size, as well as easily integrated with the other elements in a thin tablet. The overall volume of this antenna is only 30×11×4 〖mm〗^3 with a ground copper plate of 0.2mm thickness, and an area of 150×200 〖mm〗^2.
All three designs can not only supply the service to cover the current popular LTE bands but also acquire the advantages of low costs and thin shapes. They are suitable in modern devices for wireless mobile communications.
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