A study on Miniaturization of UWB Monopole Antenna using U-shaped Ground Plane

Abstract

The design of miniaturization and multi-band for terminal antennas is a research hot in recent years. The development of wireless communication technology sets higher requirement for antenna design. The main problem for terminal antenna is to cover a wide band or multiple bands in a limited volume. It is also an important research direction in the future. Many traditional methods cannot be applied any more, that is because of the complicated electromagnetic environment caused by the highly integrated and miniaturized wireless communication devices. As a result, new breakthroughs are required. In this dissertation, the problems of miniaturization and multi-band operation are studied. From the point of basic working principles of antenna, some new methods are introduced and feasible specific designs are also presented. Besides, the applications in terminal antennas validate the effectiveness of the proposed methods in obtaining the desired radiation characteristics. This thesis can be divided into the following parts. Firstly, miniaturized techniques for terminal antennas are studied. After combining these theories, we designed a miniaturized UWB antenna. The proposed antenna consists of a rectangular radiating patch with two cuts at the two lower corners of the radiating patch and U-shaped ground. Due to the U-shaped ground and the cuts of the radiating patch, the proposed antenna achieves a wide bandwidth of 2.9GHz~15.3GHz. Compare to other UWB antennas, the proposed antenna has a smaller size and a simple structure. In addition, thedesigned antenna can be easily fabricated on FR4 substrate. Secondly, multiband techniques for terminal antennas are studied. After combining these theories, we designed a small printed monopole antenna for ultra UWB (3.1~10.6GHz) and Bluetooth (2.4~2.48GHz). The proposed antenna consists of a small U-shape UWB radiating patch and a lollipop-shape Bluetooth radiating patch. This antenna is fed by a microstrip line and built by RF-4 dielectric substrate having a thickness of 1.6mm. The size of the designed antenna is "15mm×26mm" , which is significantly smaller than the previous similar antenna. The simulated and measured results show that the proposed antenna achieves a broad operating bandwidth of 2.95~11.5GHz for UWB application, and 2.38~2.52GHz for Bluetooth application. And the designed antenna has an omnidirectional radiation patterns and stable gain. At last, a RFID (Radio Frequency Identification Technology) tag by using the designed monopole UWB antenna has been designed. Using the coupling theory, a high-Q L-shaped microstrip band-rejection resonator used as the RFID tag resonating unit. The RFID tag has four resonating units, they are respectively coupled with the main transmission microstrip line to form 16 kinds of the retransmission tags.