| Due to advantages of anti-interference,strong penetration,high resolution and high peak power,ultra-wideband time-domain antennas are widely used in both wireless communication and military fields.By adjusting the relative position or excitation of the units,the more complex beamforming and higher gain can be obtained by the antenna array.At present,there are few studies on ultra-wideband time-domain antenna arrays,which mainly focus on Vivaldi antennas.Because of the advantages of low profile and low cross-polarization,tightly coupled dipole array has become a research trend in recent years.Therefore,in this thesis,the time-domain design of tightly coupled dipole array is mainly focused on,and the time-domain performance is analyzed.Firstly,the Gaussian signal and the time-frequency characteristic parameters involved in antenna design are briefly introduced.Besides,the working principle of tightly coupled dipole array to realize the ultra-wideband performance and the beam scanning of time-domain antenna array are elaborated.Secondly,the time-frequency conversion characteristic of antenna is analyzed by Fourier transform.Based on the Fourier transform formula in synthesizing far-field timedomain waveform of antenna,the factors,affecting the peak voltage of that,are divided into parameter term and loss term.Furthermore,the parameter term depends on the pulse width and element spacing,while the loss term is related to the matching performance of the antenna,the radiation efficiency and the nonlinear phase term in the far-field region.Since the phase loss caused by nonlinear phase term cannot be quantified by the group delay,the phase efficiency is proposed in this thesis.When the excitation signal and the element spacing are determined,by ignoring the loss term and limiting the synthesis bandwidth,the idealized far-field time-domain waveform of antenna in the beam scanning direction and the contribution of each frequency to the peak voltage are obtained.Thirdly,a linearly polarized tightly coupled dipole array with ±45° beam scanning ability is proposed,and the element spacing is a wavelength of high frequency.Under the excitation of pulse signal,the far-field time-domain waveform with high peak voltage can be realized.The problems of both resonance and impedance matching under the large element spacing are solved by the horizontal arrangement and wide design of dipoles.Besides,the operating bandwidth is broadened by loading of the resistive card.In the frequency domain,the antenna achieves an UWB bandwidth of 0.6 ～ 6 GHz(VSWR <3.5)with the radiation efficiency better than 70 % in most frequency bands,and the phase efficiency of broadside and H-plane scanning close to 1.In the time domain,the excellent time-domain waveform and high peak voltage characteristic are realized.Fourthly,the dual-polarized form is designed.The dipole layer is designed to be interdigital,and the impedance matching,the radiation efficiency,and the peak voltage are further improved by the matching layer.The short-circuit column is adopted on the coupling patch,moving the E-plane scanning resonance frequency out of the high frequency band.The frequency bandwidth is 0.6 ～ 6 GHz with VSWR < 2.5,the radiation efficiency better than 80%,and the phase efficiency close to 1,in most of the band.Besides,it also has good time domain waveform and high peak voltage characteristics.To validate the simulated performance of the proposed antenna,a 5×6 dual-polarized antenna array is fabricated and measured.The measured S parameters and far-field performance demonstrate the superior properties of the design. |
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