Research Of Differential UWB Antennas And MIMO Antennas

Nowadays, the communication systems have increasingly high demand for RF antennas. The differential antennas and the UWB system as well as the MIMO technology are three important research directions in the field of antenna and microwave due to their attractive advantages. The differential antennas can be directly integrated with differential circuits and decrease the energy loss of systems and thus contributes to highly integration and miniaturization of the systems. Since the permit of civilian application in 2002, the UWB system has attracted increasing attention because of its wide bandwidth, high data-rate wireless transmission, and low power dissipation. The MIMO technology can reduce multipath fading effectively and increase transmission capacity and data rate without using additional frequency sources. Therefore MIMO technology is considered as the key technology in the 4G(LTE). The present study is a combined research of differential antennas, UWB system and MIMO technology. Several antennas with good performance is presented in this dissertation and summarized as follow.1. A single-layer differential CPW-Fed notch-band tapered-slot UWB antenna is proposed. In order to achieve the sharp and controllable notch-band characteristic, one pair of halfwavelength stubs and slits are introduced inside the tapered slot and in the circular patches, respectively. Compared with a single-ended CPW-fed UWB antenna, the proposed antenna has lower cross polarization. Since all of the structures are printed on the same layer of the substrate, it can be fabricated easily and very suitable to be integrated with the RF front-end circuits.2. Two differential UWB antennas with common-mode suppression are proposed. The two antennas have special slot structures etched in the ground and fed by the microstrip in the front side. By proper layout, high common-mode suppression characteristic can be achieved and not be affected by frequencies. In addition, four types of resonators are introduced in the first antenna and two sharp-selectivity notched bands are obtained. And two types of resonators are introduced in the second antenna to achieve single sharp-selectivity notched bands.3. A Planar Wideband MIMO Antenna is designed. The simulated results show that the MIMO antenna achieves a wide bandwidth of 105.7% from 0.87 GHz to 2.82 GHz, fully covering the 2G bands of GSM900/GSM1800/GSM1900, 3G bands of TDSCDMA/WCDMA/CDMA2000 and most of the 4G(LTE) bands. The isolation is better than 12.5 dB in the lower band and 15 dB in the higher band. The planar structure and good diversity performance make the MIMO antenna very suitable for mobile terminals like smart phones.4. Two differential MIMO antennas are proposed. They are UWB-MIMO antenna and WiMAX-MIMO antenna. The two antennas both have two pairs of differential ports and the differential ports of each antenna share its radiator, thus the overall size of the MIMO antenna can keep compact as the antenna element. Additionally, by arranging two pairs of differential ports orthogonally in the virtual ac ground of each other, dual-polarization with high isolation are obtained.