Research On Dual-Band Antenna Over EBG Structure And Band-Notched Uwb Antenna

With the popularity of wireless terminals in recent yeas, wireless communication technology has developed rapidly due to its convenience and easy access. As a core component of communication systems, the antenna is faced with the challenge of high gain, low profile and miniaturization. EBG (Electromagnetic Band Gap) structure has two important characteristics, surface wave band gap and in-phase reflection band gap, which can be used in combination with antennas to improve antenna performance. On the other hand, over the designated ultra-wideband (UWB) operating band, there are some existing narrowband wireless systems, such as Worldwide Interoperability for Microwave Access (WiMAX) system and Wireless Local Area Network (WLAN) system. To mitigate the potential interferences between UWB system and narrowband systems, it is desirable to design the UWB antennas with multiple band-notched characteristic.Based on the above background, the work in this thesis mainly includes the following few aspects.Firstly, the corresponding equivalent circuit models of the two band gaps are presented. According to the models, theoretical analysis is made to study the mechanism of the two gaps. Then analysis of how to improve antenna performace with the corresponding band gap is made to design antennas combined with EBG strutures. At last a brief simulation procedure in HFSS software is introduced.Secondly, an artificial magnetic conductor (AMC) unit with dual in-phase reflection frequency bands is presented. And a unidirectional dual-band monopole antenna with low profile and high gain is obtained after combining the antena with the AMC reflector and careful adjustment. More specifically, the AMC reflector is placed right under the G-shaped dual-band antenna with a total height of only6.8mm. The combined antenna obtains a peak gain of7.2dBi and an overall gain enhancement of3.1dB in2.4-2.48GHz frequency band. Simultaneously, a peak gain of7.2dBi and an overall gain enhancement of3.4dB is obatined in5.15-5.35GHz frequency band. To further confirm the function of improving antenna performance, the performance of an double T-shaped monopole antenna after loading the AMC reflector is also researched.Finally, a dual and a triple band-notched UWB antenna are presented by combining the radiating patch oriented method with the feed line oriented method. The band-notched UWB can filter the interferences from existing wireless systems working over3.3-3.6GHz,5.15-5.35GHz and5.725-5.825GHz. This simple approach has the advantage of independent control of both the bandwidth and center frequency. Due to weak coupling between band-rejected elements, we can finely modulate any notch band by altering the relevant element without influence on others. Analysis of the approach is illustrated to verify its advantage of notch-frequency independent tunability from the aspects of S-parameters and impedance properties.