Design Of Wideband Array Antenna Based On Tightly Coupled Structure

The traditional phased array antenna has a relatively larger size due to the space between units.It is also not conducive for further expansion of antenna bandwidth.The main trends of array antenna are compact structure,broad bandwidth and planarization nowadays.The tightly coupled array antenna,which expands the antenna bandwidth by utilizing the coupling effect between elements,has become a hot issue in the field of phased array antenna.Since Professor Wheeler proposed the infinite current sheet model,the research on tightly coupled array antenna has undergone deep developments,but there are still some problems such as low low-frequency gain and single function.The tightly coupled concept is firstly applied to the design of near-field and far-field shared-aperture antenna for radio frequency identification(RFID)application.Tightly coupled structures are loaded to enhance the magnetic field intensity in near-field mode and gain in far-field mode.Then the artificial magnetic conductor(AMC)is combined with planar tightly coupled array antenna to improve low-frequency gain.Finally,the shared-aperture concept is used to design two structures,including ultra-wideband tightly coupled array antenna with integrates low-frequency dipole with high-frequency dipole and tightly coupled structure with absorption and radiation properties,which further improves the efficiency of aperture,expands the bandwidth of tightly coupled antenna and possible application scenarios.Detailed work is described as following:Firstly,to design high-performance near-/far-field shared-aperture antenna for RFID application,this paper applies the tight coupling idea to the design process.The coupling effect between antenna and surrounding structure is utilized to enhance the near-field magnetic field intensity and far-field gain.The simulated and measured results show that this design is feasible.The principle of dipole antenna,reconfigurable antenna and tight coupling involved in the design also provide reference for the following work.Secondly,to solve the problem of low gain in low-frequency band of tightly coupled array antenna,a planar tightly coupled array antenna loaded with AMC structure is proposed.After simulation of AMC unit,the tightly coupled antenna and AMC structure are combined.The simulated and test results show that the AMC structure proposed in this paper can effectively improve the low-frequency gain of tightly coupled array antenna.Thirdly,aiming at solving the problem of insufficient bandwidth of planar tightly coupled array antenna,a shared-aperture planar tightly coupled array antenna is proposed,which integrates high-and low-frequency tightly coupled dipole antenna into the same aperture.The simulated and measured results show that this method can effectively solve the problem of insufficient bandwidth of planar tightly coupled antenna.Fourthly,to expand function of the tightly coupled array antenna,this paper combines the resistor-loaded absorber with the planar tightly coupled array antenna.It can realize a tightly coupled structure with radiation and absorption functions through PIN diode switching.Relevant simulated results show that the proposed structure with dual functions has excellent performance in both states,which lays a foundation for expanding the application of tightly coupled array antenna.