The Research On Wideband Signal Generating By PLL With Frequency Sweeping Technology

The wide-bandwidth, miniaturization and low power consumption are the key components for signal source of MiniSAR system. The method of wideband chirp(LFM) signal generation with frequency sweeping by PLL is investigated for MiniSAR application. A LFM signal source at Ku-band is designed and relieazed with a scheme where DDS drives PLL to generate wideband signal. It has the characters of wide bandwidth and low distortion of amplitude and phase, while meeting the demand on miniaturization and low power consumption.Firstly, the theories and mathematical models of DDS and PLL, spuriousness of DDS output signal, noise model of PLL and their technical characteristics are introduced. Secondly, the scheme of generating wide bandwidth LFM signal with the DDS driving PLL is introduced, as well as analysis of the feasibility of using this scheme to achieve Ku-band LFM signal output. Then, on the basis of the scheme, PLL frequency-sweeping modes are discussed: frequency-sweeping reference in PLL and frequency-sweeping with frequency-division-ratio in PLL. The technical characteristics of this two kinds of frequency-sweeping modes are analyzed and compared. For MiniSAR application we choose the frequency-sweeping reference in PLL. In view of the demand for the output signal at Ku-band, three kinds of specific PLL phase-locked way are investigated including phase-locked directly at high frequency band, phase-locked at low frequency band then mixing to high frequency band, and mixing to high frequency band in loop phase-locked. The scheme of mixing in loop phase-locked is choosed after comprehensive compared.At last, the wideband signals generating by PLL frequency-sweeping are presented in detail, such as chips selection and related parameters setting method are introduced, system interfaces and key circuit are designed, etc. The signal source has been tested and the results show that the output signal spectrum is flat in band with spurious suppression up to 35dB as well as good pulse compressing performance. Also, the signal source which is small volume, light weight and low power consumption can meet the demand of miniaturization of MiniSAR.