| By synthesizing wide bandwidth from narrow instantaneous bandwidth signals, airborne stepped-frequency ground penetrating radar systems meet the requirements of higher resolution and less attenuation. Low altitude airborne platforms with high mobility need high pulse repetition rate and signal-noise ratio, thus request radar transceivers to have lower phase noise and as higher frequency switching speed as possible. In this thesis, aiming at solving the above challenges for using stepped frequency radar systems on low-altitude platforms, the author studies the generating and receiving technology of ultra-wideband stepped-frequency signal, and implements a ultra-wideband stepped-frequency radar transceiver system.Firstly, three types of ultra-wideband signals are discussed, and then inter-pulse stepped-frequency signal is chosen and studied. Taking into account of the radar operation mode, the primary parameters of the transceiver system are analyzed and calculated.Secondly, common approaches to synthesize ultra-wideband signals and reduce frequency switching time of synthesizers are introduced and analyzed. In this thesis, an pipelining structure of synthesizers is designed, and the corresponding system structure is designed.Then, a fixed intermediate-frequency receiver architecture based on constant base band up-conversion circuits which can reduce phase noise is designed. And based on this architecture main modules of the transceiver system are designed, thus a high-speed and low-noise ultra-wideband stepped-frequency transceiver system is implemented.Finally, for testing the transceiver system been designed, a method to evaluate the performance of step frequency switching time is proposed, as there are a number of indicators having fuzziness in definition and measurement. And the transceiver system has a good performance and high reliability. So, it has been applied for testing in someone airborne ground-penetrating radar. |
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