| In wireless communication system,as two important components of RF-front,antennas and filters are designed and optimized according to the impedance standards,respectively,and then connect them with transmission line.However,it will cause waste of system size and deteriorate system performance.Hence,considering the whole performance of filter and antenna and integrating the antenna and filter into a single module which is called filtering antenna can not only save the size and weight of system,but also improve the performance of RF-front.Meanwhile,the demands in high speed and large system capacity communication promote the development of broadband filters and antennas.On the other hand,in order to adapt to the complex communication environment,further increase the data transmission rate and improve the spectrum utilization,reconfigurable antenna and MIMO antenna have been widely explored and researched by many scholars.In addition,due to the advantages of high linearity,high common-mode(CM)suppression and low noise etc.,differential circuits are widely used in the radio frequency systems.Differential antenna which is excited by differential signal can be directly connected with differential circuit without using balun,which will enhance the integration and performance of the system.The main work and innovations in this paper are summarized as follows:1.In second chapter,paper mainly introduces the basic theory of classical monopole antennas and multi-mode resonators.Based on that,the filtering antenna is designed by using filtering design method which replaces the last resonator and load of filter to antenna.The resonant frequency of antenna is located between first two resonant frequencies of multi-mode resonator,and finally forms a three-step filtering antenna with controllable bandwidth.Compared with the conventional antenna,the designed filtering antenna has good in-band matching performance,good selectivity at the passband edge,and flat gain frequency response.2.In third chapter,based on the broadband filtering antenna,a pattern reconfigurable broadband filtering antenna is proposed by introducing quasi-Yagi structure.Two metal strips are added on back metallization and connected to ground plane through PIN diodes,respectively.When the PIN diode is in ON condition,the strip will work and act as a reflector,and thus,the pattern is toward to another direction.Because the four resonant modes are well distributed as the original design and the resonant frequency of antenna is located between first two resonant frequencies of multi-mode resonator,the bandwidth and in-band characteristic of filtering antenna remains unchanged under different operation states.Finally,the pattern reconfigurable filtering antenna with a fractional bandwidth(FBW)of 25% at 5.2 GHz is designed and manufactured.The measured results are well followed designed ones.3.In fourth chapter,under the research on slotline resonant antenna and differential feeding network,a differential filtering antenna is presented with high CM suppression.Under CM operation,the differential antenna does not work because the vertical electrical field is hardly introduced on the slotline radiator.Furthermore,four filtering antenna elements are distributed centrosymmetrically along the center of the substrate.The adjacent two filtering antenna elements are placed perpendicularly with a spacing of 0.05λA.Compared with the single filtering antenna,filtering performance of the MIMO antenna has no significant change.For demonstration,differential filtering antenna and MIMO differential filtering antenna which have a fractional bandwidth(FBW)of 25% at 5.2 GHz are simulated and measured.The measured results are well followed designed ones. |
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