Research On Array Antenna And Broadband Absorber Based On Tightly Coupled Structure

Tightly coupled array antenna is different from traditional wideband array antenna in the selection of element spacing,which avoids the problem that gave bandwidth and grating lobe to consideration in design.In the traditional array,the grating lobe will be generated during high frequency scanning when the element spacing is too large,and the array bandwidth will be affected by the strong mutual coupling when the element spacing is too small.The element spacing of the tightly coupled array antenna is slightly smaller than the half wavelength of the highest frequency,which avoids the grating lobe in the high frequency scanning.And the lowest operating frequency is expanded to realize ultra-wideband by introducing coupling capacitance to cancel the dipole's inductive reactance to the ground at low frequency.In addition,the tightly coupled array antenna also has the advantages of low profile and easy to be conformal with the platform,which is consistent with the development direction of phased array radar.It has high research value and received high attention.However,the tightly coupled array antenna still faces some challenges in engineering applications.In this dissertation,the tightly coupled array antenna is studied and designed according to the engineering requirements.The main contents of this dissertation are summarized as follows:1.The equivalent circuit of the modular tightly coupled array antenna is analyzed.The periodic short circuit point caused by the grounding plate is suppressed by introducing a resistance film structure between the radiating patch and the ground plane,so as to appropriately improve the antenna height.These measures provide conditions for using broadband exponential gradient coaxial balun to replace the unbalanced feeding structure.Aiming at the problem that the edge truncation effect causes to the deterioration of the performance of the finite period array,the active VSWR in the normal directional and 45 degree directional of the array is compared and analyzed when loading various methods to suppress the truncation effect.A finite array with 10×10 cycles is simulated,and the edge truncation effect is suppressed by loading lumped resistance to the parasitic elements at the array edge.The measured results show that the array achieves 5.6:1 bandwidth with a beam scanning range of ±45° and Active VSWR<3.0.2.Combined with the engineering requirements,a design scheme is proposed to cover2?18GHz applications by using a frequency division tightly coupled array antenna.Based on the design scheme of frequency division,the tightly coupled array antennas in 2 ? 6GHz and 6 ? 18 GHz bands are designed respectively.For the high frequency band array antenna,the vertical dipole,balun and periodic structure superstrates is integrated to one vertical substrate,which not only reduces the weight of the superstrates,but also facilitates the antenna manufacturing.In view of the high profile of low frequency antenna,which may block the wide-angle scanning beam of high frequency array,a planar periodic structure superstrate is proposed.The planar periodic structure is used to replace the vertical periodic structure,the antenna height is reduced to 3/4 of the original within a beam scanning range to ±45°.The feasibility of the design is verified by the simulation results of high and low frequency common array.3.The application of tightly coupled technique in non-phase scanning antenna is studied.(1)A wideband vertical polarization omnidirectional antenna is proposed by combining the tightly coupled structure with the traditional omnidirectional antenna design method.The omni-directional radiation is formed by four subarrays which evenly distributed in the azimuth plane.One-dimensional tightly coupled array with the broadband characteristics is adopted for the subarray of the antenna.The measured results show that the relative bandwidth of 93% and the maximum gain of 8dbi are achieved,and the roundness of the omni-directional radiation pattern is less than 2.5d B.(2)Based on the idea of tightly coupled,a wideband circularly polarized antenna is designed.the tightly coupling between the two offset cross dipole elements is used to enhance the bandwidth of the element.According to the design principle of circularly polarized antenna,the dipole element is excited by a feeding network with broadband equal amplitude and 90° phase difference.Simulated and measured results show that the impedance bandwidth(VSWR < 2)of the proposed wideband circularly polarized antenna is 102.7%,and the axial ratio bandwidth is 94.2%.An overlapping bandwidth between impedance and axial ratio is 94.2%,and the gain is about6 d Bi.4.The broadband absorber is studied based on the application requirements of absorbing surface in tightly coupled array antenna.According to the frequency response characteristics of the split ring,the lumped resistance is loaded on the periodic split ring to form a wave absorbing structure.In view of the narrow working bandwidth of the absorber composed of a single size split ring resonator,a multi ring resonator structure is proposed,in which multiple split ring resonators with different sizes are randomly arranged and combined according to the same period.The structure combines the operating bandwidth of multiple single resonant rings and shows broadband absorbing characteristics.An absorber sample with 10×10 periodic elements and 2.8 mm profile height is simulated and manufactured.The measured results show that the absorptivity of the absorber to normal incident electromagnetic wave is more than 80% from 7.9GHz to 18 GHz.