Transient Antenna And Its Applications In Ultrawideband Radar

In recent years, transient antennas have many applications in transient electromagnetic area, such as Ultra-wide band (UWB) communication, UWB radar, surface-penetrating radar and electromagnetic compatibility. The performances of these antennas are resulted from their capability of radiating or receiving transient signals with rapidly time-varying performances. Signal waveform transformation or distortion take place due to radiation or reception by transient antennas. In most of appointed application areas, the signal waveform is carrier of useful information, so it is very important for special application that the rigorous study of such signal waveform transformation or distortion, which can enrich the theory and technology of transient electromagnetic.Transient antenna and its application in UWB radar are involved in this thesis. Some theoretical and technological issues are discussed to some extent, including transient radiation theory, transient antenna design technique, UWB radar design and transient scattering calculation and measurement. The main contents are outlined as follows:(1) The retarded potential is used to derive the transient radiation characterization of general space-time source distribution both in near and far zone, based on the time domain Maxwell equations. Transient radiation is characterized by its short-time effect and can be described and represented by projection transform and impulse radiation characteristic. The finite during period of radiated electromagnetic field is decided by the projection extent of source distribution and the time width of exciting pulse.(2) Three kind of TEM horn antennas are analyzed and designed by means of numerical calculation, electromagnetic simulation and experiments. Their reflection and radiation characteristics are obtained. The similarities and differences between TEM horns and traditional narrowband antennas are discussed and summarized.(3) A 200~800MHz UWB radar experiment system is fabricated, which can accomplish the acquisition, transformation and restoration of 600MHz bandwidth transient signal. The analog quadrature demodulation is adopted in the sampling receiver of the experiment system, so A/D sampling requirement is reduced and moreover, the received signal can be restored from the in-phase and quadrature channel signatures.(4) A time-domain scattering measurement system is fabricated and valuable transient scattering data of many typical metal targets are obtained. These targets include sphere, plate, cylinder, missile model and some plane models. These data is a good begin to study of target transient scattering characteristics.(5) The commercial general modeling software package such as AutoCAD?and FDTD algorithm are combined to calculate the transient scattering of simple and complex targets. The calculated results are compared with theoretical or measured results and good agreement is obtained.