| Analysis on transient electromagnetic scattering for targets has always been a very active research topic which has extensive researches and uses in multi-disciplinary fields.It has a lot of practical applications in military and civilian.As the transceiver of UWB system,the UWB antenna is indispensable in the experiment of transient electromagnetic scattering.In this dissertation,transient pulse scattered from metal and dielectric objects and the design of UWB antenna are the research topics.The main research contents of this dissertation include the following aspects:1.Transient pulse scattered from metal disk and metal cylinder objects is studied.Metallic reflection of electromagnetic waves is due to the large number of free electrons in metal.Free electrons,driven by the electromagnetic wave,will vibrate in response to the current inside the surface.Induced current radiates electromagnetic wave into space and conduct current penetrates into metal and dissipates energy.Three kinds of mechanisms,including the specular reflection,edge diffraction and creeping wave are considered.Then we give the dynamic equation of the free electrons and calculate the scattered field and RCS through the solutions of electron velocity in time-domain and frequency-domain.At last,we analyze the characteristic of scattered pulse.Simulated,measured and theoretical results have a good agreement with each other,which indicate the proposed method is feasibility on analyzing transient electromagnetic scattering of metal objects.2.Transient pulse scattered from dielectric disk objects are studied.Unlike metal objects,the dielectric target scattering electromagnetic wave is dependent on the internal electric dipoles.Driven by the electromagnetic wave,dipoles are forced to rotate and the oscillating dipoles emit electromagnetic wave outward.We give the rigid body dynamic equations of the dipoles and calculate the scattered field and RCS through the solutions of dipoles'angular velocity in time-domain and frequency-domain.Simulated and theoretical results have a good agreement with each other,which indicate the proposed method is feasibility on analyzing transient electromagnetic scattering of dielectric objects.3.A miniaturized UWB antenna with three notched-bands is researched and designed.The proposed antenna has a compact size of 24×30 mm~2.The concentric split-ring slots structure with a higher VSWR is used on a circular monopole antenna.The structure is very simple and feasible to obtain notched-band at different frequency by adjustment of the length of slots.The proposed antenna has three notched-bands,located at 3.52-3.81 GHz for WiMAX and 5.03-5.42 GHz and 5.73-6.17 GHz for WLAN,respectively.Through software simulation,the surface current distribution of the antenna a obtained and analyzed.The proposed antenna has been fabricated and measured and it is shown that it has a broadband matched impedance(3.05–14 GHz,VSWR<2),stable gain and good omnidirectional radiation patterns.4.A miniaturized UWB-MIMO antenna is researched and designed.The proposed antenna consists of two identical UWB elements.The ground stub structure is introduced between the two elements.It changes the surface current distribution,makes the surface current truncated and drawn,and obviously expands the bandwidth and improves the isolation between the ports.The miniaturized MIMO antenna and measured mutual coupling lower than-15d B,covers the 3.1-10.6 GHz UWB band.Simulated and measured results have a good agreement.The proposed UWB MIMO antenna is suitable for UWB wireless communication systems.Meanwhile,it has a simple structure and a compact size of only 30×40 mm~2,easy to process,has good application prospects. |
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