Studies On Ultrawideband Wide-angle Scanning Arrays Based On Tightly Coupling Technique

Modern wireless system needs to achieve various functions,such as communication,navigation,detection and sensing.In general,these functions operate at different frequency bands.The system used many antennas to cover these frequency bands in the previous applications,leading to large-size and high-cost.In recent years,the multifunction system,which used single ultrawideband(UWB)aperture to cover all operating bands,was used to replace the previous system;thus,the cost of the system was greatly reduced.With the development of the electronic technology,this advanced concept has been widely promoted,and the abundant application scenarios also put forward higher requirements for antenna array.To satisfy the requirement of the multi-function system,many ultrawideband antenna arrays have been proposed.Among them,the tightly coupled array has received immense attention recently due to its excellent performance.Although ultrawideband tightly coupled array has been widely studied,there are still some problems to be solved,such as complex structure and limited scanning angle.To solve these problems,this dissertation studied the analysis and design method of the ultrawideband wide-scan array based on tightly coupling technique.The works mainly include following two parts.The first one is wide-angle impedance matching technique,and the second one is scanning angle expanding technique.The works of this dissertation are summarized as follows:1.Study on wide-angle impedance matching technique of planar tightly coupled array based on frequency selective surface(FSS)structure loadingFirstly,we study the analysis method based on spectral Green's function for the transversely connected capacitively-coupled dipole array.By modifying the transverse current distribution on the surface of the dipole,the method can be used to accurately calculate the input impedance of the transversely connected capacitively-coupled dipole array.The result shows that the dipole has low input impedance,allowing the array to match with the 50 ? coaxial easily.Then,we proposed a fully planar tightly coupled array,whose element is transversely connected capacitively-coupled dipole.By loading FSS structure,the proposed array can work in 3.7:1 bandwidth for scanning up to 60° in all planes.However,it is hard to further improve the scanning performance of the array,because the trend of the wave impedances for TE and TM modes wave are different with the change of incident angle.To solve this issue,we proposed a polarization-sensitive FSS structure to serve as the wide-angle impedance matching layer.The effective dielectric constant of the FSS structure for the TM mode incidence wave and TE mode incidence wave can be changed respectively by different structural parameters;thus,the impedance of the E-and H-planes scanning performance can be adjusted respectively.Thanks to the feature of the proposed FSS structure,the array with the polarizationsensitive FSS structure loading can scan up to 75° in the E-plane and 60° in the H-plane in 3.7:1 bandwidth.Finally,an 11 × 11 prototype is fabricated and measured to verify the feasibility of the design.2.Study on wide-angle impedance matching technique of vertical tightly coupled array based on multilayer metallic strips loadingWe proposed a vertical tightly coupled dipole array loaded with multilayer metallic strips.A new equivalent circuit model(ECM),which is more accurate than traditional ECM,is proposed to help analyze and design the tightly coupled dipole array.The loaded multilayer metallic strips can help achieve smoother impedance transform from the dipole to the free space,thus,can help improve the performance of the array.With the help of the ECM,the proposed tightly coupled dipole array can achieve 6.2:1 bandwidth while scanning to ±60° in all planes by optimizing the structural parameters of the metallic strips.Meanwhile,thanks to the loaded multilayer metallic strips,the array can avoid complex feeding structure,resulting in a light-weight and low-cost array.3.Study on scanning angle expanding technique of the time-domain array based on pattern reconfigurable antennaWe propose to use pattern reconfigurable technique to expand the scanning angle of the time-domain pulse radiation array.An ultrawideband pattern-reconfigurable antenna is designed,and we studied the energy pattern and the fidelity of the antenna.The element used two p-i-n diodes to control the antenna working at three different modes,and the beamwidth of the energy pattern can jointly cover ±70° under three modes.The linear array,which is composed by eight reconfigurable antenna elements,can scan its main lobe of the energy pattern from-70° to +70°.Meanwhile,the simulated and measured fidelities are larger than 0.75 on the main lobe direction during scanning.4.Study on scanning angle expanding technique of the wideband array based on true-time-delay lensWe propose to use true-time-delay lens to expand the scanning angle of the wideband array.A receive-transmit(R-T)lens unit cell based on tightly coupled dipole is designed.The gradient surface,which is composed by the proposed true-time-delay lens unit cells,can achieve the same refractive index for electromagnetic waves in 7 to 11.5 GHz.Then,a one-dimensional Vivaldi array is simulated and the results verified that the designed gradient true-time-delay lens can expand the scanning angle of the wideband array from40° to 60°.In addition,this technique can be used to expand the scanning angles of the following two types of arrays:(1)the beamwidth of the active element pattern of the array is narrow;(2)the grating lobe will appear while scanning to large angle due to the large unit spacing.