| Ocean environment affects human economic activity and national defense construc-tion, especially in coastal area where happened frequently activities. The real-time and effectively monitoring of inshore ocean dynamics parameters could avoid the losses of coastal economy affected by poor ocean enviroment, and provide scientific basis which could improve the nearshore marine environment. By theory and technology constraints, radio ocean remote sensing technology is difficult to apply in nearshore area. From the current research, UHF radar has the characteristics of high resolution and sensitive to changes in ocean dynamics parameters, which has a good development prospects in do-main of inshore monitoring. This paper aims to design an full-digital multi-channel UHF radar receivers for inshore dynamics parameters mornitoring.The principle of detecting ocean environment parameters with UHF radar is used the Doppler shift formed with radio and wave’s Bragg scattering to obtain the radial ve-locity of currents relative to the radar. The operating frequency of UHF radar is set to340MHz, adopt frequency modulated interrupted continuous wave (FMIC W) mechanism which could make the transceiver work together, the15MHz sweep bandwidth assures high range resolution of radar. The main goals of radar designed in this thesis is detect-ing ocean dynamics parameters and moving targets, implementing multipurpose radar system for ocean monitoring and port management. Radar is composed of synchronous controller, frequency synthesizer, analog front-end, digital modules, antenna system and transmitter.This thesis focuses on radar receiver, including synchronization controller, frequency synthesizer, analog front-end, digital modules and other sub-modules. Different from the classic superheterodyne receiver, this design is realized without analog mixer and local oscillator signal generator, the system structure is simple with less analog circuits, pulse compression process is completed in the digital domain.In order to ensure radar system normal and stable working, synchronization con-troller provides stable synchronization and status signals to submodule, each signal keeps strict timing relationship. This design used field programmable gate array (FPGA) to re-alize synchronization controller of radar system, it is relatively simple and programable real-time. The system designed in thesis is coherent Doppler radar, frequency synthesizer pro-vides the system with the desired reference signals. In order to ensure the coherence of system, all reference signals in system are from TCXO in frequency synthesizer. UHF radar system used Direct Digital Frequency Synthesis (DDS) chip AD9910produced by ADI company to generate chirp signal with carrier frequency of340MHz and bandwidth of15MHz as transmitted signal. The reference signal of DDS is set to983.04MHz and provided by any-rate precision clock chip-Si5324which is produced by Silicon Labs and based on Silicon Laboratories’3rd-generation DSPLL technology. The chips mentioned above could implement parameters configuration through online programming, it is con-venient and flexible.Analog front-end plays the transceiver controlling, filtering and RF echo amplifica-tion roles, the structure is relatively simple. Amplifier module uses three order’s amplifi-cation structure, overall gain of single channel is38dB. An analog front-end circuit board contains four independent channels, two boards can meet the system needs of8channel.Digital module contains analog digital conversion, data processing and transmission sub-module. Echo signal after filtering and amplifying in analog front-end is directly RF sampled by analog digital conversion module. System uses ADI’s AD9265chip to implement analog to digital conversion, sampling rate is81.92MHz, sampled signal is transmitted to data processing module for subsequent processing. CORDIC algorithm is used in system to realize dechirp and digital downconversion processing, after filtering unwanted signals, data is transferred to the host by USB to achieve twice FFT processing for extracting the distance and velocity information of targets. Finally, system uses a FPGA chip to complete eight channels’ real-time and parallel processing of dechirp and downconversion in digital domain, which making the system more compact.The Yagi antenna is used in system with gain of11dB and half-power beamwidth of45degree, which could realize transceiver antennas replacing. In field test, the transmitter with power of10W and100W is used in system, radar system can achieved ocean echo detection of the most range of5Km with100W transmitter.System specifications test and close-loop test are completed in lab, the results meet the requirements of field experiments. August2012, the research group went to Zhoushan City Zhejiang Province for the principle experiments of ocean dynamics parameters de-tecting with a period of20-days, verifying the correctness and practicality of hardware circuit, timing control, signal processing and other aspects of system. Through compar- ative experiments of different locations, obtaining ocean echo spectrum with different forms in the conditions of typhoon weather and different height of antenna. Through summarizing of the first principle field test and system debugging, the second experiment of ocean surface dynamics parameters detecting was conducted during March2013in Li-uao Town Fujian Province, the system can independently and real-time work with eight channels, the farthest distance of detecting achieves5Km. Through data analysis, obtain-ing the expression of windturbine in the form of UHF radar echo spectrum, and receiving ocean echo spectrum under different sea conditions. The new method of wave height extraction with UHF radar is found by observing lots of data and referring to the way of waves extracting with HF radar, and comparing with the result of wave height measured by satellite, the trends of both is analogous. Comparing experiment of different polar-ization of antenna was conducted during field test, obtaining ocean echo spectrum under different polarization, the power of received ocean echo is the strongest when transmit-ting and receiving antennas are worked in vertically polarized way, and the power is the weakest when transmitting and receiving antennas are worked in horizontally polarized way, it is suitable for target detection.The close-loop tests in lab and the experiments provide that the design of UHF radar system is successful, meets the requirements of design. |
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