| Summary: | 碩士 === 國立交通大學 === 電信工程研究所 === 98 === In this thesis, a new microwave component named current driver is proposed, which is capable of inducing ground edge current for radiation. Since the current driver serves as a small feeding structure with little contribution to radiation, it can be designed very small while good radiation properties are maintained. Compared to the miniaturized antennas, the approach that utilizes ground plane as the main radiation has smaller size and better antenna performance. Furthermore, a circuit model of the miniaturized balun (balanced to unbalanced transformer) is introduced to explain the current inducing mechanism and to provide some valuable physical insights into the properties of the current driver. The effect of a shielding metal box for the proximity circuitry near the current driver is also investigated. It is shown that the nearby shielding box has minor effect on the performance of the driver, which demonstrates the feasibility of the current driver for antenna applications in a compact wireless terminal.
Given the benefits shown above, two antenna applications based on the current driver are presented. Both of them are fabricated on the low cost FR4 substrate of 0.4 mm. First, the current driver for WLAN 2.4 GHz designed with a lumped capacitor or printed capacitor has a small size of about 4 mm × 4 mm. The good radiation properties are obtained at 2.45 GHz with the measured radiation efficiency over 60 % and the nearly omni-directional radiation pattern with the average gain of about 0 dBi. Secondly, the dual-band current driver for WLAN 2.4/5/2 GHz applications is achieved by combining two single-band current drivers with the overall size of about 8.5 mm × 4 mm. The measured radiation performances at 2.4 GHz are similar to the ones for the previous single 2.4 GHz current driver, which has the measured antenna radiation efficiency higher than 60 % and nearly omin-directional patterns. At 5.2 GHz, the measured radiation efficiency is reduced to about 50 % due to the high dielectric loss caused by the FR4 substrate in the high frequency. The nearly omni-directional patterns are still maintained. The simulation and measurement results come to a great agreement. Based on the compactness and design flexibilities, the current driver is feasible for wireless applications
|
|---|
