Research On Miniaturized And High-performance Filtering Antenna Based On Fusion Design Method

The rapid development of wireless communication system has put forward the requirements of integration,miniaturization,and low-loss for Radio Frequency（RF）devices.As two important devices of RF front-end,the integrated design of antennas and filters helps to improve the integration of RF system and reduce system loss.Meanwhile,the high out-of-band suppression performance of filtering antenna can effectively reduce the mutual coupling between antenna elements of different frequency bands and help to reduce the spacing of them,thus realizing the miniaturization of multi-band shared-aperture antenna system.Therefore,the design of filtering antenna has become a research hotspot of antenna fields in recent years.Among the various design methods of filtering antenna,the fusion design method has been widely studied due to its significant advantages in size and performance.This method makes use of radiation nulls to realize stopbands for high frequency selectivity and out-of-band radiation suppression.Based on the fusion design method,this dissertation aims at the requirements of high-performance filtering antennas arising from the miniaturization of RF front-end and cross-band interference in multi-band communication system,and focuses on the technology of achieving radiation nulls under the conditions of ensuring low in-band loss and antenna miniaturization,and then provides methods of generating radiation nulls in antennas for various applications cases.The main research contents and innovations of this dissertation are as follows:1.A method of changing the current distributions on the corresponding resonant structures of the lower and higher frequencies of the antenna is proposed for achieving radiation nulls.With this method,on the designed miniaturized ultra-wideband（UWB）antenna with a tilt-folded patch feed,by loading different types of slots according to the current distributions,the radiation nulls at the lower and upper band-edges are realized,and the frequency selectivity is improved without increasing the size of the UWB antenna and without decreasing the in-band radiation performance.This method improves the problems of large size and high-loss caused by conventional cascading UWB bandpass filter and UWB antenna,and provides a way to improve frequency selectivity under conditions of miniaturization and low-loss.2.To further enhance the out-of-band suppression level of filtering antenna in a miniaturized structure,a method of constructing multi-path coupling structure in antenna is proposed to achieve radiation nulls.By introducing the U-shaped radiation patches and dual coupling slots in a microstrip antenna,not only the impedance bandwidth is expanded,but also multiple electromagnetic（EM）waves coupling paths are constructed in antenna.The phase difference of EM waves between different paths is utilized to generate three controllable radiation nulls and improve the frequency selectivity.Moreover,an improved Composite Right/Left Hand（CRLH）transmission line with EM band-gaps in specific frequency bands is proposed to further improve the out-of-band suppression level without decreasing the in-band radiation performance of the antenna.The filtering antenna designed with this method achieves wideband,high frequency selectivity and high out-of-band suppression simultaneously in a miniaturized structure of 0.4λ₀×0.4λ₀（λ₀ is the free-space wavelength at the center frequency）.3.To further expand the harmonic suppression bandwidth,a method of generating frequency-controllable radiation nulls with various slots in a low-profile structure is proposed,and then combining them to extend the harmonic suppression range.By adding shorting pins,radiating-edge slots,I-shaped slots,and complementary open loop slots to microstrip antenna,surface current distribution on the radiating patch is changed,thus expanding the impedance bandwidth and realizing four independently controllable radiation nulls in a low-profile of 0.0375λ₀.The frequency selectivity of the antenna is enhanced with the radiation nulls at the band-edge.Also,by combining two radiation nulls at the higher frequencies,the harmonic suppression range is extended to 3f₀,and the gain of harmonics is reduced to less than-10 d Bi.This method provides an effective solution for extending the harmonic suppression range of filtering antenna with low profile.4.To realize a miniaturized dual-polarized filtering antenna,based on the unique electromagnetic properties of metasurface,a method by employing the change of reflection phase and surface wave propagation constant of a double-layer metasurface to generate radiation nulls is proposed.By adjusting the space between each layer of the metasurface,not only the miniaturization is realized,but also a radiation null in the upper stopband is obtained with its 180°reflection phase;Another radiation null in the lower stopband is obtained with the change of the propagation constant of Transverse Magnetic（TM）surface wave by metallized vias.Furthermore,Center-Shorted Square Split-Ring（CS-SSR）resonant structure with two transmission zeros is designed,and combined with the double-layer metasurface and vias for designing a dual-polarized filtering antenna,finally the antenna obtains four independently controllable radiation nulls.With these four nulls,the lower and upper roll-off rates and out-of-band suppression level of the antenna are substantially improved in a small size of 0.56λ₀×0.56λ₀.The proposed method of radiation null generation can realize the design of miniaturized and high-performance dual-polarized filtering antenna.This dissertation based on the fusion design method of filtering antenna,focuses on the realization of the radiation nulls,and carries out the relevant theoretical research,software simulation,fabrication,and measurement verification.For different application and demands,the method of realizing frequency controllable radiation nulls is gradually improved,which provides systematic design guidance for the design of miniaturization and high-performance filtering antenna,thus helps to promote the application of filtering antenna in wireless communication systems.