| Ultra-wideband(UWB)technology has been rapidly developed due to its high transmission rate,low energy,low cost and high security,and has been applied to communications and medical fields.In particular,the Federal Communications Commission(FCC)released 3.1GHz-10.6GHz for commercial applications in 2002.The UWB technology has been widely studied both in industrial and academic fields.UWB antenna is one of the key components in the UWB communication systems.The performance of the antenna may affect the communication quality of the entire system.First,the UWB system has wide impedance bandwidth,which overlaps with many used narrow band systems.In order to void or reduce the potential interference between the UWB systems and these utilized narrowband systems,design band-notched UWB antenna with small size is significant.Next,it need design a new antenna when the antenna works in different modes,especially for the UWB antenna covering the entire operating band,which will increase the cost the antenna design.A reconfigurable antenna can not only cover the entire band UWB band but also provide a filtering characteristic for UWB communications.Once again,with the development of the wireless communication,the spectrum is limited,which can be solved by using cognitive radio techniques.A cognitive radio UWB antenna aims to alleviate the shortage of spectrum resources by means of the reconfigurable characteristics.Finally,multiple-input multiple-output(MIMO)communication systems have high capacity,high efficiency and resist to multipath interference,and have been used to improve the quality of wireless communications.Thus,research on the design of MIMO-UWB antenna is attractive based on the MIMO techniques.This thesis was mainly study on the UWB antenna and application with high performance.The filter techniques,switch and MIMO technologies were studied via theory analysis,electromagnetic simulation and experimental measurement to exploit high performance UWB antennas.The band-notched characteristic and the reconfigurable functions were widely investigated,which included the filter design,cognitive radio and MIMO techniques.Theory analysis,modeling,simulation and experiment methods were employed to develop high performance UWB antennas.The research contents and the findings are summaried as follows.First,a T-shaped stub and an impedance stepped resonator were used to design a band-notched and dual band-notched UWB antenna to reduce the potential interference between the UWB systems and the WLAN and X-band.The proposed band-notched antennas avoided the electromagnetic leak and effectively suppressed the potential interference from WLAN-and X-band.The proposed band-notched UWB antennas were simulated and verified by the measurements.The results showed that the proposed band-notched UWB antennas can cover the entire UWB band and provided filtering functions in the WLAN and X-bands.The proposed band-notched UWB antenna were realized by the integration of the stub and stepped impedance resonator,which provided desired band-notched functions and can provide attractive anti-interference characteristics.Next,a four-mode reconfigurable UWB antenna was proposed by controlling the filtering functions to aovid the duplication of the UWB antennas.By controlling the states of the switches,the proposed four-mode reconfigurable UWB antenna can act as a UWB antenna,or a band-notched UWB antenna,or a dual-band antenna and even or a tri-band antenna.The proposed reconfigurable UWB antenna was compatible with UWB antenna and band-notched UWB antenna,which is easy to realize multi-antenna integration.The design method was analyzed,while the band-notched functions and the reconfigurity were studied.The simulation and experiment results demonstrated that the resonance characteristic of the stepped impedance resonator can be switch ON/OFF by using these switches,which was viable,effective and correct.Once again,one-and two-port UWB antennas for cognitive radio applications were proposed by controlling the states of the band-notched UWB antennas based on the defected microstrip line and switches techniques to overcome the shortage of spectrum resources.These proposed cognitive radio UWB antennas with one feed port can work in underlay andoverlay modes,which effectively solved the spectrum shortage caused by the spectral overlap.For the one-port cognitive radio UWB antenna,it operated in overlay mode on the basis of the band-notched UWB techniques,which can reject the interference from detected narrowband signals.A wide slot UWB antenna and a narrowband antenna were designed independently and combined together to form a two-port cognitive radio UWB antenna,which made the UWB system and the narrowband system work at the same time.Also,the proposed antennas improved the spectrum efficiency.Finally,a coupling reduction technology using radial line loaded stub is proposed to solve the large coupling between MIMO-UWB antenna elements in portable terminals.A two-element MIMO-UWB antenna with a radial line loaded structure was investigated in detail.By inserting a radial line loaded structure into the ground plane between the two antennas,the current go along the radial line loaded structure,which reduced the array element coupling and improved the isolation.Simulation and measurement results verified the viable and correctness.The isolation of the MIMO-UWB antenna is better than 15dB. |
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