Studies On The Key Problems Of Two-dimensional Wideband Wide-angle Scanning Tightly Coupled Phased Arrays

Two-dimensional wideband wide-angle scanning arrays are widely used in multifunction radio frequency(RF)system,electronic warfare,radio telescope,high speed data communication,and imaging systems.In recent years,tightly coupled dipole array(TCDA)outperforms the other candidates due to its advantages of low profile,low cross-polarization,wideband,and wide scanning angles.Even if some achievements have been made,some problems remain unsolved.This dissertation starts with the principles of the TCDA and focuses on the wideband feeding network,impedance transformer and superstrate to improve the performance of the TCDAs.The works of this dissertation are listed as follows:1.Studies on radiated power improvement under a finite radiation perture based on oversampled TCDATraditionally,the radiated power can be improved by expanding the radiation aperture size of the antenna array or increasing input power of the unit cell.However,the radiation aperture size is always restricted by assembly space.The input power improvement of the unit cell is always limited by the signal source.It is useful to arrange more elements and improve total efficiency of the antenna array to improve radiated power on a finite radiation aperture.A high permittivity substrate and compact wideband balun are used for miniaturization of the antenna array.The period of the unit cell is only0.146?_h×0.146?_h(?_h is the wavelength at the highest operation frequency in free space).Parameters of the balun are optimized to improve impedance matching between the balun and the antenna array.Double-layer bilateral frequency selective surfaces(FSSs)are used to replace traditional dielectric superstrate to improve impedance matching between the antenna array and free space.A low-loss dielectric substrate is used to reduce dielectric loss of the antenna array.In these ways,the total efficiency is greatly improved.The simulated and measured results show that the proposed antenna array shows wideband wide-angle scanning properties and high radiation efficiency from 1.73 to 5.46 GHz.Compared with the designs in literatures,this design can be used to improve radiated power on a finite radiation aperture.2.Studies on ultra-wide angle scanning TCDA based on integrated feeding network and FSS superstratesThe impedance match issue is a major challenge in the design of ultrawide-angle scanning TCDA.To overcome this issue,a multi-stage wideband balun is employed and designed synergistically with the dipole element to improve impedance match performance at wide-angle scanning in the E plane.The working mechanism of the FSS superstrate is studied.The capacitance of the FSS superstrate is used to counteract the inductance at the upper face of the antenna array to improve impedance match at wide scanning angles in the H plane.Consequently,the proposed TCDA has a bandwidth of2.4:1(2.1-5GHz)with Active VSWR<3,while scanning up to 80°in the E plane,70°in the H plane,and 75°in the D plane,respectively.Due to the substrate with a low permittivity and strong coupling of the feeding structure,the proposed antenna array shows characteristics of low cross-polarization.A 16×16 prototype was fabricated and measured,showing good agreement with the simulated results.Compared with the designs in literatures,this design shows wider scan range and a better figure of merit.3.Studies on TCDAs with low cross-polarization based on Vivaldi antenna structureThe commonly used stripline-slot broadband balun and exponential gradient structure,which are widely used in the Vivaldi antenna,are introduced into the design of the TCDA.The design difficulties of broadband feed structure and impedance matching of tightly coupled dipole arrays are solved.A double-sided feeding structure is adopted and the two arms of the dipole are printed on the same plane of the substrate to reduce the electric field component perpendicular to the plane.In this way,the cross-polarization of the TCDA is lowered.The two-layer dielectric superstrate placed above the antenna array is used to improve the scanning performance in the H plane.The proposed TCDA has a bandwidth of 4.1:1(1.35-5.54 GHz)with active VSWR<3,while scanning up to 80°in the E plane,45°in the H plane,and 65°in the D plane,respectively.The profile of the TCDA is only 0.14?_l(?_l is the wavelength at the lowest operation frequency in free space).The cross-polarization ratio is below-72 d B at broadside radiation,below-62 d B at 80°scanning in the E plane,below-28 d B at 45°scanning in the H plane,and below-9.5 d B at 65°scanning in the D plane,respectively.A 16×16 prototype was fabricated and measured,showing good agreement with the simulated results.Compared with the designs in literatures,this design shows a relative low profile and lower cross-polarization.