| The rapid development of wireless communication will inevitably lead to the search for new technologies that can provide large amounts and high data transmission.Ultra-wideband（UWB）systems have attracted a lot of attention because of their wide bandwidth,abundant spectrum resources,strong anti-interference ability and high data transmission rate.Nowadays,mobile terminal equipment is moving towards portability,so it is necessary to design miniaturized antennas,especially in compact devices with limited space.There are other narrowband signals in the UWB band that cause interference to the communication system and need to be filtered,and it is important to design UWB antennas that trap baud.UWB system is limited to the application in the field of short-range communication,multiple-input multiple-output（MIMO）technology has the characteristics of spatial multipath and multi-channel signal parallel transmission,combining UWB technology and MIMO technology to improve the ability to resist multipath fading,enhance the channel capacity of the wireless communication system,and realize long-distance stable transmission of signals.In order to adapt to the requirements of microwave equipment for different frequency bands and avoid repetitive antenna manufacturing caused by the change of single antenna performance,the design of reconfigurable antennas has become a new direction of research.This thesis mainly focuses on the miniaturization,wide bandwidth,multi-notch,reconfigurable and high isolation characteristics of UWB-MIMO antennas.The main work of this article is as follows:Firstly,two small-size multi-notch UWB antennas are designed.The first antenna is a three-notch UWB slot antenna,the front side adopts a circular radiation patch,the back adopts a mushroom-shaped gap etched with a floor,the radiation patch is etched with an inverted U-shaped groove,a pair of C-shaped parasitic branches are coupled next to the microstrip feeder,and a pair of Z-shaped branches are parasitic on the ground plate to achieve the three-notch characteristics of WIMAX,WLAN and ITU 8G bands,the size of the antenna is 30mm×24mm×1mm,The working bandwidth is 2.82～12GHz,and the gain is maintained at 2～4.6d Bi outside the notch band,which has stable radiation performance.The second antenna is a five-notch UWB antenna,which uses slotting and parasitic branches to effectively filter out the WIMAX,5G,WLAN,X-band downlink and ITU 8G bands.The size of the antenna is only 25mm×16mm×0.8mm,the working bandwidth is 3.1～12GHz,the gain is kept in the range of 2～3.6d Bi outside the notch band,and the radiation performance is generally good.Secondly,two UWB-MIMO antennas are designed.The first antenna is a two-unit UWB-MIMO antenna,with a radiation patch etched on the front side of the complementary square resonance ring（CSRR）and two pairs of C-shaped resonant branches parasitizing on both sides of the gradient microstrip feeder,effectively suppressing the four narrowband bands of WIMAX,WLAN,C-band and X-band downlink.The parasitic step-shaped decoupling branch in the center of the floor on the back achieves high isolation.The results show that the antenna is in the range of 2.89～12GHz with|11|<-10d B,|21|<-20d B,the gain is maintained at 2～4d Bi outside the notch band,and the radiation characteristics are stable.The second antenna is a four-unit UWB-MIMO antenna,which has a compact size of 42mm×42mm×1mm,achieving an impedance bandwidth of 3.09～12GHz and an isolation of less than-16.4d B.The diversity characteristics of the antenna with ECC<0.02,DG>9.991d B,TARC<-20d B,total group delay value less than 1.4 ns,peak gain of 2～5.1d Bi,and good radiation characteristics.Thirdly,a reconfigurable UWB antenna based on complementary notch and narrowband band based on open-loop resonator is designed.At first,the relevant transmission characteristics of a pair of single-ring S-shaped SRR loaded on the coplanar waveguide is studied,and the analysis shows that the SRR coupled to the coplanar waveguide（CPW）feeder has a band-reject function,and the twisted layout can switch between the two states of fundamental resonance to second resonance.The same effect can be achieved by replacing the S-SRR diagonal transmission line with a pin diode.In order to obtain multiple resonances in the frequency band,varactor diodes are introduced that can be continuously adjustable from the primary resonance to the second resonance.Further research shows that by loading a pair of pin diodes between the CPW and the coplanar ground gap,the structure allows the SRR transmission characteristics to switch between band stop and bandpass by controlling the opening and turning of the pin diode.This structure is easy to apply to printed monopole antennas,and finally a planar UWB antenna using S-SRR structure is proposed.The antenna realizes the reconfigurable characteristics of complementary notch and narrowband band,and is verified by simulation experiments.The frequency band range of the UWB antenna is 2.82～12GHz,and when the pin diode is disconnected,it presents notch characteristics,realizing continuous adjustment in the range of WIMAX to WLAN notch band;when the pin diode is on,it presents narrowband characteristics,realizing continuous adjustment from WIMAX to WLAN narrowband band.The antenna gain is maintained at 2.5～4.6d Bi in the notch UWB antenna except for the notch frequency band;the gain is about 1.2d Bi in the narrowband state,and the radiation characteristics in the two modes are stable. |
