Wall Radar Stepping Source Design

The Through-wall radar system applications are increasingly widespreaded. Particularly the Through-wall radar system plays a major role in the earthquake disaster reliefing life-detection as well as working in anti-terrorism, riot, etc. All those applications are pushing the rapid development of Through-wall radar systems. A major development direction of it is portable, hand-held and highly integrated direction. In a Through-wall radar system, one of the core components is the signal source module; its performance is highly related with the performance of the whole system. The combination of Direct Digital Frequency Synthesis and Phase Locked Loop technology provides an excellent solution for radar signal of the Through-wall radar system.First the basic concept of Through-wall radar and its trends are introduced, and then the through-wall radar system based on the ultra-bandwidth is discussed in detail. Second the specialist of the ultra-bandwidth through-wall radar system that in practical application is analyzed, and the various parameters of a Through-wall radar signal was got. Then the Direct Digital Frequency Synthesis and Phase Locked Loop technology was introduced, and the combination of technologies was described. And also the new frequency synthesizer program by combining DDS and PLL is discussed.This final design of the signal source circuit is using PLL which is inspired by DDS. This solution dominates the merits of DDS such as super fine frequency resolution, high frequency accuracy and easy programmed with excellent character of narrow-band tracing filter of PLL to completely achieve the demands of the system. The DDS and PLL chips are controlled by MCU chip-C8051 of the frequency synthesizer. The output signal of the DDS is the excitation signal of the PLL multiplier. And the signal goes through the PLL to get a signal which meets the requirements of Through-wall radar system. This paper presents a detailed program of the frequency synthesizer, DDS module and the main functions of PLL module. The selection and design of DDS external clock source, AD9858 hardware circuit, MCU workflow, PLL, and VCO are introduced specially. According to the system requirement, the appropriate device is selected to build the circuit to carry out a reasonable circuit layout. Finally, phase noise result and picture of spectrum with spur are presented, analysis of the result is given, and the existing problems and methods to resolve those are motioned.