| Ultra-wide Bandwidth(UWB)has been highly valued since its Birth.Traditional frequency domain measurement schemes usually require expensive anechoic chamber,while time domain ultra-wideband technology can remove background clutter effects by "time domain windowing" and "background cancellation" methods,so the measurement cost is low.The pulse signal timedomain system transmits has a wide spectral range,so broadband characteristics can be obtained in one measurement.At present,time domain measurement technology has been applied to many aspects such as electromagnetic parameter measurement,Antenna radiation characteristic measurement,RCS measurement,ISAR imaging and life feature detection.The work of this paper is based on sub-nanosecond and picosecond pulse sources and related equipment.Main tasks as follows.(1)The structure and working principle of the time domain measurement system are introduced.A reflection coefficient measurement scheme for lossless isotropic dielectric plates based on time domain free space method is designed.A method for measuring the dielectric constant of a lossless isotropic dielectric plate by using the time delay method is presented.In the experiment,the reflection coefficient of the dielectric plate is obtain by compared the propagation signal in free space with the signal reflect from the dielectric plate;When measuring the permittivity,since the velocity of electromagnetic waves in different materials are related to dielectric constant,the signal arrival time in air and in the material can be measured at the same distance and compared,from this the dielectric constant of the medium can be calculated.In this paper,the ideal metal plate,FRP(Fiber Reinforce Plastic)plate,and teflon plate are used to verify the correctness of the above two methods.(2)Using the time domain UWB radar system to locate indoor human target and detect respiratory signal.Since the pulse of the system is a picosecond-level pulse source,the resolution is particularly high,this make the radar can measure the Time Difference of Arrival(TDOA)accurately.The position of the target can be achieved by continuously detecting the TDOA of the target;the respiratory signal can be achieved by detecting the signal fluctuation caused by the slight fluctuation of the chest cavity.In this paper,a human target location scheme based on elliptic crossover algorithm is adopted.By using technologies of time domain windowing and pulse cancellation,not only can we extracting the TDOA from the radar echo of two receiving antennas,but also can eliminate the effects of background clutter and antenna coupled signals on positioning.The test results show that the proposed methods in this paper has good reliability,high positioning accuracy and good anti-interference ability.(3)In order to obtain a larger detection distance,a preliminary exploration of high power pulse source design was carried out.The pulse source is the most important part of the time domain UWB system.Its characteristics determine the basic parameters such as the bandwidth,stability and effective detection distance of the system.Based on the avalanche characteristics of the transistor and the MARX circuit principle,this paper designs two pulse sources: the first pulse source uses a single avalanche transistor circuit,which can generate a negative polarity pulse with a voltage amplitude of 112 V and a half-height width of 7ns on a 50 ohm load resistor.The second pulse source uses a multi-stage series circuit of avalanche transistor,which can generate a negative polarity pulse of 260 V and half width of 2ns on a 50 ohm load.Both pulse sources are capable of outputting stable waveform.Compared with similar products,the pulse sources designed in this paper get a balance on the pulse width and pulse amplitude.The pulse sources designed in this paper have a small volume,a relatively low cost,a stable waveform and a small jitter,those characteristics of the pulse sources are of great significance for miniaturization and practical use of UWB radar system. |
PDF Full Text Request