Pattern Reconfigurable And Broadband Microstrip Antenna Design Based On Characteristic Mode Analysis

With the development and progress of information technology,communication systems have higher and higher requirements for antenna performance.Among them,reconfigurable antennas belonging to "smart antennas" and broadband antennas with high bandwidth have received great attention,and these two antennas have also been widely used in base station communications and other fields.Characteristic mode analysis(CMA)is a physical reflection of the radiation mechanism of the antenna,which has important guiding significance for antenna design.In this thesis,two microstrip patch antennas with reconfigurable characteristics and broadband characteristics are designed using the theory of characteristic analysis and the idea of multi-mode fusion.The specific research contents are divided into the following two points:(1)Based on characteristic analysis,a reconfigurable antenna using diode switches to achieve beam switching and broadband end-fire beams is designed.The antenna uses a three-unit patch array as the radiation unit,and the metal short-circuit column is the key component to adjust the surface current of the antenna.Using the characteristic mode theory,the distance of the short-circuit column is adjusted in a targeted manner to realize the individual regulation of the resonance mode.The design of the designed feed system can make the antenna meet the mode fusion condition.Finally,diodes can be used to control the number of feeds to achieve reconfigurable characteristics.The antenna can achieve beam switching between 4GHz and 4.3GHz under the condition of single feeder.Under the condition of double feeder,the antenna can achieve the4.08～4.46 GHz frequency band.54° single beam endfire,and the maximum gain is7.34 d Bi,and the side lobe is lower than-7d B.(2)A broadband antenna is designed based on characteristic analysis.The broadband antenna continues the radiation principle of the reconfigurable antenna with dual feed points.Specifically,the characteristic mode and surface characteristic current distribution are obtained by using FEKO,and the resonance range of each mode is adjusted by adding a short-circuit pin on the antenna,so that five modes with similar resonance frequencies meet the mode fusion conditions.Similar to the feeding method used by the reconfigurable antenna,the feeding network design adopts a cross-feeding method,so that the phases of each feeding point are shifted by 180° in turn,and the excited mode resonance forms a continuous impedance matching passband.In-band antenna radiation is stable.The simulation results show that the-10 d B impedance bandwidth of the antenna is 3.7～4.53 GHz,its absolute bandwidth is 830 MHz,its relative bandwidth is about 20%,the maximum tilt angle is 72°,and the maximum gain is also 8.46 d Bi.The side lobes on the operating band are below-7d B.In this thesis,the reconfigurable antenna designed using the principle of mode fusion has the functions of dual-frequency beam switching and single-beam end-fire radiation,which has the advantages of smart antennas.In the 4GHz frequency band,the design greatly increases the bandwidth of the patch antenna,making it more potential for applications.