Research And Design Of Ultra-Wideband Source For Groud Penetrating Radar

Ground penetrating radar (GPR) provides a nondestructive detection method, which use radio waves to determine the distribution of underground media, it emits electromagnetic waves towards underground with the help of a transmitting antenna. The electromagnetic waves reflect between interfaces of different underground media, then the GPR receives the reflected electromagnetic waves through receiving antenna. So that the specific conditions of the underground media can be inferred according to the characteristics such as the waveform of electromagnetic wave as well as the changes of amplitude and time. Nowadays, the application field of ground penetrating radar (GPR) has been widen, and this paper will focus on some of the problems on present GPR such as low and narrow frequency signal source and hope to make a better adaption for a broader market.In this paper, the signal source is accomplished with help of phase-locked loop technique. A phase-locked loop includes three modules, namely, phase discriminator, loop filter and the voltage-controlled oscillator. Among these modules, the voltage-controlled oscillator is key to the whole phase-locked loop and affects the tuning bandwidth, output power, phase noise and many other factors. This paper begins with the basic theories of oscillator, focuses on the technical parameters of ultra-wideband voltage-controlled oscillator, and chooses a reasonable circuit structure of voltage-controlled oscillator to design the two ultra-wideband voltage-controlled oscillators, of which their frequency bands of 1-2 GHz and 2-4 GHz are linked together. In the end, this paper designs other modules of the phase-locked loop and connects them to the voltage-controlled oscillator for phase noise test.The VCO in L-band is designed from series of resonance network according to the theory of Colpitts feedback oscillation circuit. Testing results shows that the oscillator frequency tuning range between 1-2 GHz meets the requirements of design indexes, while the output power range of-6--2dBm still has a certain gap from the design index. The VCO in S-band is designed from parallel resonant network according to the theory of negative resistance feedback model. The testing results show an oscillator frequency tuning range of 2-3.7 GHz, and output power between 2.2 to 3.3 dBm, both meet the requirements of the design indexes. Both phase-locked loops in the VCO are tested at a center frequency of 1.5 GHz and 3.1 GHz after locking, and the phase noise are 89.13 dBc/Hz@100kHz and 85.6 dBc/Hz@100kHz respectively. Both of them meet the design requirements.