Research On Key Technologies Of Arrayed Impulse Radar

As an emerging ultra-wideband radar technology,impulse radar can be used to detect or identify the target by transmitting the impulse pulse without carrier.Because of the extra-short pulse-width and rich spectral component of impulse pulse,the impulse radar has advantages over the traditional continuous-wave radar in the distance resolution,angular resolution,anti-stealth,penetrating ability,et al.So the impulse radar has great potential applications.In this dissertation,the impulse-pulse signal source is required to output pulse with high power and low trigger-jitter,and can be easily to be synchronized for the arrayed impulse radar.The transmission characteristics of the impulse electromagnetic pulse radiated from the array will be studied to explore the basic law of energy transmission and superposition,and to analyze the reason of high resolution resulted from the radar.The physical images of the target scattering under the impulse pulse will be researched to provide a certain theoretical basis for the radar detection.In this dissertation,a semi-insulating(SI)GaAs photoconductive switch(PCSS)is used as the impulse signal-source to meet the requirement of high peak-power and low trigger-jitter.Moreover,the SI GaAs PCSS is studied by the theory and experiment.Firstly,the optical absorption mechanism of GaAs is analyzed.It is confirmed from calculation that the ionization absorption of EL2 level is the main reason for the 1064 nm absorption of SI GaAs PCSS.Secondly,under the dark-state test of PCSS,it is found that the dark resistance is not monotonically decreasing with the electric field,it even increases in the range of a certain electric field.The fluctuation of the dark resistance with electric field is analyzed with thermal-electron effect of the carrier and collisionionization effect of the impurity.Furthermore,triggered with 1064 nm laser pulse,SI GaAs PCSS was tested with linear and lock-on mode,respectively.The characteristics of the sub-linear current-voltage and the saturate output voltage show that the optimal optical energy for the linear PCSS to work is the energy when the output begins to saturate.Compared with the dark-state resistance,the on-state resistance even increases with the field higher than 3 kV/cm,which is just the reason why the linear mode PCSS has no gain.In addition,for the threshold the PCSS applied to work in the lock-on mode,there's not only the lower limit of the electric field and the optical energy,but also the upper limit of the optical energy.The high-gain dipole-domain model is put forward to make an analysis of the mechanism of high-gain under lock-on mode.Then the upper and lower limit of the electric field and optical energy,which trigger the PCSS into lock-on mode,is calculated based on this model.At last,the laser diode is used to make test on the PCSS,and the influence of the parameters of diode on the output of the PCSS is analyzed to minimize the impulse signal source.For the research on the transmission characteristics of the impulse electromagnetic pulse,the antenna model is abstracted and the Maxwell equations are used to calculate the analytical solution of the impulse electromagnetic pulse radiated from the circular antenna.Then the physical image of the radiation from the unit antenna and its energy transmission characteristics in the axis are shown form the solution.Based on these results,the unit antenna is regarded as a point source,and the point-source approximation model for array calculation is proposed.By using this model,the transmission characteristics of the impulse electromagnetic impulse are analyzed.Consequently,the characteristics of the high-efficiency energy-synthesis and the beam focusing are obtained from the model and verified by the experimental results,which makes the arrayed impulse radar has the high range and angular resolution.In addition,for the experimental phenomenon that the energy of the impulse electromagnetic pulse is rapidly attenuated with the distance,the ground reflection theory is added to the analytical formula to make analysis.The calculated results are in good agreement with the experimental results.In the following research is made on the target scattering.For the vertical incidence of the impulse pulse on the metal target,the physical and analytical solutions of the target scattering are given by using the similar method to the unit antenna radiation.The scattering characteristics of the media target are also analyzed based on the metal target scattering.The experimental results are in agreement with the analytical results.At the end of this dissertation,the integration design of the PCSS?Blumlein line?and Vivaldi ultra-wideband antenna is given,and the experiment of the impulse radar radiation system is carried out.The experimental results verify the synthesis characteristics of the arrayed impulse electromagnetic pulse again.