The Omnidirectional/Directional Switchable Antenna Based on the Curved Microstrip Antenna with Defected Ground Structure

With the quickly developing of wireless transmission, the miniaturized terminal with multi-function working in multi-frequency bands has attracted more and more users. However, with the digital circuit being packaged into chip, the terminal miniaturization has gone to bottleneck period. The microwave transmission line and antenna is difficult to reduce size, but the RF module and antenna cover more than 80% surface of the terminal and more than 60% size of the terminal. Miniaturize the dimension of the microwave circuit and antenna has been critical problem. Usually, people hope to integrate the antenna inside the terminal, and it can work in several available frequency bands with being easy conformal, high gain and expected far field. Such as the external whip antenna, it is very convenient for WLAN terminal over 2.4 GHz, 5.25 GHz or 5.8 GHz, but it is not pretty and easily to be damaged. On the contrary, microstrip antenna, slot antenna and their array are easily manufactured with low cost and can be used in WLAN system [1, 2, 3, 4, 5, 6] for good performances with low profile, lightweight. Especially, they are easy to integrated with devices.