Development Of GPR System Basing On VNA

Ground penetrating radar (GPR) is a high resolution geophysical exploration method and is widely applied in engineering task. At the present time, there are two class ingredients which restrict the development of ground penetrating radar. The first one is the improvement of performance and mechanism of GPR instrument, the other one is the improvement on exploration method, data process and interpretation. Every updating and amelioration of Ground penetrating radar instrument always make the GPR technology and application develop greatly according to the GPR phylogeny. Therefore, the system performance of Ground penetrating radar instrument takes the much important effect of GPR development. After 1990s, electronic technology, especially micro-electronics technology and digital processing technology get the great development, and that brings the ground penetrating radar technology around to a new development levels. This thesis's author develops a step frequency ground penetrating radar system (SFGPR) basing on E5071B vector network analyzer (VNA) after analyzing the GPR instrument phylogeny and the system performance of multifarious GPR system, and making some testing experiment to prove that the SFGPR system has the excellent exploration preferment. The result of this research task will provide the foundation of theory and experimentation for the finished product of GPR instrument development, and also set up an experiment platform for electromagnetic wave propagation research and electromagnetic exploration study, which has high precision data gather, much more amount of information, wade application and convenient operation.Time-domain plus GPR has the advantages: high efficiency; rapid and vertical data interpretation, but the disadvantages are: narrow frequency band, small dynamic range, low emission power, few antenna type selections, and it require high level of electro-device performance. All the disadvantages make Time-domain plus GPR difficultly apply to high resolution and deep exploration. Comparatively, frequency-domain GPR directly makes measurement in frequency domain, receives signal in vector mode, obtains the amplitude and phase information of target object electromagnetic response. It makes some necessary time-frequency domain transform and analysis to get the wave number parameter of the target object response around different frequency, as a result to achieve the aim of conductance and dielectric constant imaging. SFGPR system receive the frequency sweep signal by difference mixing technology which consumedly reduce the demand of the system hardware performance level, and improve the measurement precision and stability. Thes technolgy also improves the capability to detect the min power signal in the background of clutter noise. The SFGPR system can transmit high power signal, so the exploration depth and dynamic range of this system is improve. Step-frequency ground penetrating radar has much more advantage then time-domain ground penetrating radar. For example, wide performent frequency band width, conveniently operation, flexible choice of antenna classes, high precision, much deep exploration, high dynamic range and etc, but it also suffers form the capability and price of radio frequency device (especially the frequency synthesizer), and the system's work efficiency comparatively low and it consume lot of energy, it's preferment parameters hardly to be set up, all these make the system develop slowly.The development of SFGPR system basing on VNA utilizes the VNA instrument as a signal source and receiver. The cost of system development is quite low. Besides convenient operating, the synthetical signal form can be programmed, and the system function can be extended. SFGPR system has 300KHz to 8.5GHz wide operation frequency band width. The max average emission power is up to 10 dBm, max frequency sweep point is 1601, and measurement stacking time is arbitrary. In the task, this author had researched and developed a self-control mode data acquisition system of SFGPR and local area network (LAN) connections remote-control mode data acquisition system of SFGPR, designed a preceding small signal radio amplifier and a few sets of ground penetrating radar antenna, finally accomplished the hold hardware and software research of the SFGPR system.The detail content of this research task can classify into four sub-contents:First, particularly analyzes preferment principium of general ground penetrating radar and SFGPR system, and discusses the relationship between system parameter and exploration capability. These researches provide the parameter setting foundation for SFGPR system development.Second, demonstrates the hardware constructed scheme of SFGPR system, and designs some ground penetrating radar antenna: high frequency antenna (900MHz), low frequency line shape antenna(15MHz), constant angle logarithm helix antenna (0.8GHz to 8GHz), Vivaldi antenna (1GHz) and etc. makes a wide band preceding small signal radio amplifier to increase the receive performance. It can enlarge the signal-noise rate and system dynamic range.Third, programs the self-control mode data acquisition SFGPR system with the VBA language embedded in the vector network analyzer, makes convenience to outdoor measurement and other motion testing. After Building the LAN connection, programs LAN remote control mode SFGPR data acquisition system, and then programs the F-K data migration and data display system. As a result constructs a set of high precision, multifunctional SFGPR system.The last one, to analyze the SFGPR system exploration capability, some indoor and outdoor experiment is carried out. Experiment includes bedrock exploration, metal pipe detection in water, single layer and multilayer plastic board detection, complex structure paraffin model structure exploration and etc. the main aim is to analyze the detection resolution and signal character of the SFGPR system. At last, use the F-K migration software and another data pretreatment method to process the testing data to obtain better experiment result then raw detection data.According to the research and experiment result, SFGPR system shows out its excellent exploration capability: high exploration resolution, well adaptability, convenient operation, much amount of measurement information, high signal-noise rate, high dynamic range, and it requires the performance level of hardware much lower then time-domain ground penetrating radar at the same exploration capability. General time-domain ground penetrating radar does not take all these advantages. But SFGPR also has some disadvantages, such as that, its working efficiency is lower than time-domain ground penetrating radar, a lot of system parameters to be set up are quite complex, and data procession also complex. As a whole, development of SFGPR system basing on vector network analyzer is simple and easy. The cost of system construction is low; exploration has high precision and high resolution. This system is quite suit to scientific research organization and manufacturer to construct ground penetrating radar research and development platform and another electromagnetic wave propagation or exploration platform.