Researches On Broadband And Multi-band Planar Antennas

As key components in wireless communication systems, antennas have the effect of transmitting and receiving electromagnetic waves. With the rapid development of wireless communication technology and the improving quality requirement of wireless communication device, the demand for the performance and function of the antennas is increasing. Researchers often intend to improve the impedance bandwidth or decrease the dimension in the traditional broadband and multi-band antenna design, and pay fewer attentions to the realization of other functions of antennas. The multi-function antennas with polarization diversity, good mechanical performance and/or smart operation ability will be more suitable for practical wireless applications and will ultimately improve the performance of the entire wireless communication system. This dissertation aims at the realization of the broadband and multi-band planar antennas and attempts to resolve the disadvantages in the former antenna designs. A series of methods have been explored and summarized, which can be used in the design of multi-function broadband and multi-band planar antennas. Compact broadband and multi-band planar antennas are studied and designed. The research contents can be divided into three parts:1) ultra-wideband(UWB) planar antennas; 2) broadband circularly-polarized skin-antenna and array; and 3) multi-band planar antennas.For the UWB planar antenna design, at first a UWB planar monopole antenna with“L” shaped extended ground plane stubs is proposed, which can make the antenna produce a resonance at low frequency and improve impedance match performance at middle and high frequencies. The proposed antenna has a-10 dB impedance bandwidth that can fully cover UWB 3.1-10.6GHz band, and also realized miniaturization. Then, a miniaturized UWB dual-polarized planar slot antenna is proposed. Using two quarter-wavelength stepped-slots as its main radiators, making two radiators be orthogonally distributed, making two microstrip lines also be orthogonally distributed,the antenna can realize dual-polarized operation in a very broad operation band(97%relative bandwidth) and has a good isolation between the two ports.For broadband circularly-polarized skin antenna and array design, at first the basic concept of smart-skin antenna is introduced, especially the structure of skin-antenna in detail. Then, a broadband circularly-polarized skin-antenna is designed, which has notonly broad-10 dB impedance bandwidth and 3dB axial-ratio(AR) bandwidth, but also a good mechanical performance. And then, a thirty-two-way power divider is designed,which has low return loss and low insert loss in a broad bandwidth. Finally, using the antenna element and power divider designed before, a 4×8 skin-antenna array is designed, which has a broad-10 dB impedance bandwidth, a 3dB AR bandwidth around20 GHz, and a gain greater than 20 dBi, also has a good mechanical performance and can sustain strong strength from outside.For multi-band planar antenna design, at first a compact dual-band dual-polarized loop-slot planar antenna is presented. The dual-band characteristic is realized using a loop basic mode and a slot basic mode. Orthogonally located coplanar waveguide(CPW)feedline and microstrip feedline, and a rectangular slot radiator make the antenna can realize dual-polarized performance. Then, a dual-band circularly polarized planar monopole antenna for WLAN/Wi-Fi applications is presented. The radiator of the antenna is composed of a “C”-shaped metal strip and an “L”-shaped metal strip. Both its-10 dB impedance bandwidths and 3-dB AR bandwidths fully cover all the2.4/5.2/5.8-GHz WLAN bands and all the 2.4/5.5-GHz Wi-Fi bands. And then, we design a compact tri-band dual-polarized planar monopole antenna with asymmetrical ground plane and loaded stub. The asymmetrical ground plane and loaded stub make the antenna obtain circularly polarized performance in the higher band, linearly polarized in the lower and middle bands. Finally, a compact tri-band planar monopole antenna for GPS/WLAN applications is designed.