Análise e construção de um circuito gerador de pulsos UWB para aplicações de radar de penetração de solo

Abstract

This work presents the development of a low complexity and low cost UWB pulse generator circuit for GPR applications. The rst objective of the dissertation is to choose an UWB pulse suitable for GPR applications, therefore, dierent types of pulses are analyzed and dierent UWB pulse generator circuits are reviewed from the literature. Hence, two generator circuit topologies are proposed and evaluated through simulations. The topologies used in UWB pulse generators consist of four stages: square wave generator, delay stage, a triangular pulse generator and a pulse modulator lter. The rst topology uses a triangular pulse generator circuit based on the NAND gate and the second topology uses a triangular pulse generator circuit based on the NOR logic gate. As a result, a short gaussian pulse is generated, which is converted into a second order derivation pulse using a pulse modulator lter circuit. The architectures of the circuits proposed in the this work are adapted to design and implement an electronic circuit capable of generating UWB pulses using BJT transistors with high frequency of transition, operating as a switch circuit, achieving rise and fall times in the nanosecond-order. The electronic circuit board was built using FR-4 substrate and discrete components. The design based on the NAND gate presents a pulse measured on 50 load with duration of 79 ns. The second project based on the NOR gate shows a second derivative Gaussian pulse, with width of 1.47 ns and pulse repetition frequency of 2 MHz. Finally, the pulse is evaluated according to the requirements of the GPR multilayer problem.