Abstract: An ultrawideband (UWB) adaptive transmitter capable of transmitting a train of very short pulses has been developed. The objective is to demonstrate the feasibility of an UWB radar design which is capable of transmitting a train of 200 picosecond pulses. The transmitter uses a unique approach to generate the required train of short pulses by simultaneously transmitting all the frequency spectral components of the pulse train. By using a stable source for each spectral component and coherently transmitting these signals through a wideband antenna which has a common phase center for all the spectral components, a train of short pulses is formed in space. This approach differs from the other conventional approaches which generate the short pulses in real time by switching the RF transmit signal on and off in picoseconds. In this transmitting signal, multiple transmitters are used to generate the required power aperture product for detection and the high power problem often encountered in the real time pulse generator is alleviated. In addition, high average power can be radiated by transmitting a long coded train of closely spaced short pulses. A trade-off study has been carried out to determine the design parameters and the required transmitter components. In order to achieve phase coherency in all the transmitter, a common master oscillator is used to feed a set of phase-locked oscillators. These phase-locked oscillators provide the required frequency accuracy, spectral purity, low noise, and frequency stability. These transmitter signals are radiated through a broadband multiplexing feed which illuminates a reflector forming a high gain beam. The broadband multiplexing feed has a common phase center for all the spectral components. Thus, a coherent summation of all the transmitter signals can be accomplished to form the required train of short pulses in space. A complete demonstration model of the ultrawideband transmitter has been developed, fabricated, and tested. The performance of the transmitter has been verified in an outdoor far field range. An analysis has also been made to compute the synthesized waveform. The measured short pulse waveform is shown to be in good agreement with the calculated result. The details of the development will be presented.!0
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