Key Techniques For Metamaterial Loaded Low-profile Ultra-wideband Tightly Coupled Phased Arrays

Phased array antenna is a type of array antennas that can adjust the amplitude and phase of the array element rapidly and accurately through electronic control technology,which can be used to realize the flexibly control of beam directions,the reduction of sidelobes,the regulation of pattern nulls and so on.It has long been a research focus in the field of antennas.With the rapid development of wireless electronic technology,a new generation of radar systems is developing towards a multi-functional integrated radio frequency system,which will be used to realize the coordinated combat capability integrated with detection,intervention,detection and communication.The design indicators of the new generation of carrier platforms are becoming increasingly strict,and their on-board antennas have to take all the radiation performances,conformalbility to the platforms and the stealth characteristics into consideration.Moreover,the new generation of wireless mobile communication system needs to deal with the increasing number of equipments,more complicated communication environment and limited channel capacity.Traditional phased array antennas are obviously difficult to meet the urgent application requirements,whereas the type of tightly coupled phased arrays with ultra-wideband,wide angle scanning performance and low profile characteristic becomes a very attractive solution.The tightly coupled phased arrays are derived from a reverse thinking of the array forming method.The coupling between array elements,which the traditional array tries to eliminate,is effectively used as a new degree of freedom,thus reducing the antenna profile and greatly broaden the operation bandwidth.In recent years,many studies on ultra-wideband tightly coupled arrays have been reported.However,some practical problems such as insufficient bandwidth expansion,high overall profile and limited scanning angle still exist.Moreover,the realization of multiple excellent performance in a single aperture is a great technical challenge.The ultra-wideband tightly coupled dipole array loaded with metamaterials is deeply studied in this dissertation,and technical breakthroughs are made in the aspects of bandwidth enhancement and profile reduction.The combination of multiple excellent performance such as ultra-wide bandwidth,low profile and wide angle scanning in a single antenna aperture is also achieved.The main work and innovation are summarized as follows:1.A low cross-polarization ultra-wideband tightly coupled balanced antipodal dipole phased array is proposed.Although the traditional ultra-wideband antennas,such as Vivaldi antennas,have the relatively wide operating frequency band,there still exist some disadvantages such as limited scanning angle,poor cross-polarization performance or high profile,which can not meet the performance required by modern radar and communication systems.In this dissertation,a low cross-polarization ultra-wideband tightly coupled balanced antipodal dipole array is proposed by combining the idea of tightly coupled antenna,balanced antipodal dipole structure and metamaterial loading.The proposed array adopts a threelayered balanced antipodal dipole structure,which effectively reduces the transverse electric field generated by the dipole radiation and thus improves the cross-polarization performance.The triangular patch at the end of the dipole is used to introduce the coupling between the elements and expand the operation bandwidth.A type of full split ring metamaterial wide-angle impedance matching layer is loaded so that the antenna is able to achieve wide angle scanning performance.A 16 × 16 array prototype has been fabricated and measured.The results show that the array can achieve E-plane ±60° and H-plane ±45° scanning at 2.05～10.3GHz.The measured cross-polarization level is better than-28 d B at broadside,and the overall profile is only 14.9mm.2.A ferrite-loaded ultra-low profile ultra-wideband tightly coupled dipole array is proposed.For low-frequency systems,the antenna profile determined by the operating frequency is increasingly difficult to meet the limited installation space on the new generation carrier platform.Therefore,the phased array antennas with ultra-low profile have considerable research value.In this dissertation,an ultra-low profile ultra-wideband tightly coupled dipole array is proposed,where the high permeability and dielectric constant characteristics of ferrite materials is utilized to reduce the phase velocity of electromagnetic waves.By this method,the equivalent height between the antenna and the groundplane is increased,which means the reduction of the actual profile.In addition,this design also uses a vertically placed double-Y balun to achieve balanced feeding.The cross type frequency selective surface is used to improve the dielectric loss caused by ferrite.Wide-angle scanning performance is achieved by loading a fully split ring metamaterial structure on the top.A 6 × 8 array prototype has been fabricated and measured.The results show that the proposed array is able to operate at 0.2～2GHz with± 60° wide angle scanning in the E-plane and H-plane.The overall profile is only 62.5mm,which means 0.042 times the wavelength at the lowest operating frequency.Among the known tightly coupled arrays with ten-octave operation bandwidth,it has the lowest overall profile.3.Study on the resistive material loaded ultra-wideband tightly coupled dipole array and the edge effect suppressionEdge effect refers to the sharp deterioration of the array performance caused by the truncation of the array edge.In order to suppress the edge effect,traditional method is to load a certain number of dummy elements on the edge of array.However,this method reduces the effective area of antenna aperture.Although the tightly coupled arrays have been rapidly developed in recent years,there is little research on the mechanism and new suppression methods of edge effect.In this dissertation,a 10-octave ultra-wideband tightly coupled dipole array loaded with resistive material is designed firstly.Through the loading of interdigital resistive material and double-layer wide-angle impedance matching layer,the bandwidth,scanning performance and radiation performance are guaranteed.Then,from the physical level,RLC circuits are loaded on the edge of the array to eliminate abnormal resonance.From the algorithm level,the feeding amplitude and phase are optimized as degrees of freedom to further improve the active voltage standing wave ratio performance.Through the above design,a 6 × 8 scale array prototype is fabricated and measured.The operation bandwidth is 0.2～2GHz,with dual polarization characteristics and ±60° scanning in E-plane and H-plane.The measured results verified the effectiveness of the proposed approach by the combination of algorithm and hardware loadings,which makes a valuable contribution to the practical application of tightly coupled phased arrays.