| With the rapid development of wireless communication and increasing requirement of wireless devices, the antenna is becoming increasingly important as the basic key element of mobile terminal products. Recently the design of miniaturized antenna for wireless local area network(WLAN) applications has become urgent. The existing communication protocols for WLAN contain IEEE 802.11 a, IEEE 802.11 b, IEEE802.11 g, IEEE 802.11 n, IEEE 802.15(Bluetooth), Home RF and so on.In this thesis dual-band linearly polarized printed slot antennas and dual-band circularly polarized printed slot antennas are studied based on the related achievements at home and abroad. The principles of dual-band and circular polarization are generalized. In order to satisfy the requirement of WLAN at 2.4GHz-2.484GHz/5.15GHz-5.35GHz/5.725 GHz-5.825 GHz, two dual-band linearly polarized printed slot antennas and a dual-band circularly polarized printed slot antenna are designed in this thesis. The main contents and contributions of the thesis are as follows:(1) Based on the theory of the slot antenna, a dual-band linearly polarized printed slot antenna fed by CPW is designed. A wheel-shaped slot is applied to this antenna.The dimension of the design is decided by the lowest working frequency required by WLAN. Parameters of the slots in the center of the patch are adjusted to realize resonance at higher band. Finally a dual-band antenna is achieved. The measured result shows bandwidths of this antenna reach 330MHz(2.39GHz-2.72GHz) and1180MHz(4.85GHz-6.03GHz) which satisfy the requirements of WLAN.(2) An antenna using ring and cross slots is designed on the basis of the wheel slot antenna. In order to realize better omni-directionality and low cross-polarization, the patch of the antenna is circular. Finally the measured result shows that the lower band of the antenna ranges from 2.3GHz to 2.53 GHz, and the higher band divides to two bands which ranges from 4.88 GHz to 5.47 GHz and 5.68 GHz to 5.94 GHz.(3) A rectangular dual-band circularly polarized printed slot antenna fed by CPW for WLAN applications is designed. This antenna achieves circular polarization by grooves and an L-shaped branch. Finally at lower band the antenna can realize LHCP in direction of +Z and RHCP in direction of-Z. At higher band the antennacan realize LHCP in direction of-Z and RHCP in direction of +Z. The fabricated antenna has been made and measured. The result shows the antenna works at2.04GHz-3.12 GHz and 4.96GHz-5.44 GHz, and the band of 3d B axial ratio are2.38GHz-2.5GHz and 5.15GHz-5.35 GHz. |
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