Pll-based Real-time Tracking The Dds Chirp Source Research

At the beginning, the developments and the basic theory of the LFM (linear frequency modulated) sources are introduced briefly. Next, the methods of generating the LFM sources are analyzed.After analyzing the advantages and disadvantages of the traditional LFM schemes, a novel LFM scheme of the real-time tracking the Direct Digital Synthesizer (DDS) by the Phase Locked Loop (PLL) is proposed. Through the merit of the fast frequency-hopping of the DDS and the real-time tracking of the PLL, the LFM source ranges from 5.76GHz to 5.92GHz with high linearity is achieved. The waveform is triangular frequency modulated wave with modulation bandwidth 160MHz, modulation period 400μs, step frequency 16 kHz, and step time 20ns. Compared with the traditional schemes, the new scheme is characterized by the following features: high linearity, high stability, immune to environmental influence, etc. These features are demonstrated in the experiment, providing the theoretical and technical support for the application.In the end, the experiment of the closed-loop distance measurement was conducted, using the length of the coaxial-cable to simulate the distance of the object. The results show that the LFM source can be used to measure the target distance. And the difference frequency reflects the distance information. The results of the distance measurement validate the feasibility of the scheme of the LFM.