The Research Of Ultra-wideband And High Performance Microwave Frequency Source Based On DDS

With the rapid development of modern radar technology,ultra-wide-band frequency synthesizer,with low phase noise,low spur,fast frequency hopping and high output frequency,has become main trend of frequency signal generator research.In the widely used linear frequency modulation continuous wave(FMCW)radar system,linear chirp signal source is an important prerequisite for achieving excellent system performance.A high performance wideband frequency synthesizer using technology of combining Direct Digital Frequency Synthesis(DDS)with Phase-Loop Locked(PLL)is presented in this paper.And a C-band frequency synthesizer with working band of up to 4GHz and low phase noise is successfully designed.The main research work of this paper includes:(1)An overall system scheme of C-band broadband frequency synthesizer is designed and presented in this paper.According to the overall performance requirements of a millimeter wave FMCW radar system,the parameters of wideband frequency synthesizer are determined.In order to meet the requirements of rapid scanning,low phase noise and low spurious,the DDS direct excitation PLL scheme is proposed by investigating the existing frequency synthesis technology and combined with specifications.At the same time,the principle of the scheme is elaborated,and the key indexes are analyzed and simulated.(2)DDS frequency synthesizer based on AD9914 chip is fabricated.The key technologies to be solved include high-order multiplier link circuit design;high-speed digital and analog circuit electromagnetic compatibility design;MCU control program design and debugging.In order to get the low phase noise of the DDS reference clock signal,28 times multiplier chain is designed by using step recovery diode and excited at TCXO.Experimental results of 2800MHz multiplier chain shows that the output power is 0.3dBm,the harmonic suppression is better than 55dBc and the phase noise which is consistent with the software simulation data and the theoretical calculation data is better than-123dBc/Hz@100kHz.This RF signal can be used as the reference clock for AD9914 chip.The control circuit of DDS frequency source is designed by application of MSP430F5529 microcontroller.Software flow chart design and programming is an important guarantee for the successful operation of the microcontroller.In PCB drawing,the problem of high-speed digital and analog circuit electromagnetic compatibility design is fully considered.The broadband DDS module was successfully fabricated after a lot of debugging of hardware and software.From the measurement,DDS frequency synthesizer covers the rang 500MHz to 1000MHz,the phase noise is better than-130dBc/Hz@100kHz and the sweep period is 20ms.The DDS frequency synthesizer provides a low phase noise reference signal for a subsequent wideband frequency source.(3)C-band broadband lock-loop frequency source is fabricated in this paper.The phase detector of the C-band phase-locked loop frequency synthesizer selects a digital phase-frequency detector HMC439 with extremely low additional noise.The phase detector not only reduces the phase noise of the PLL frequency source,but also has the characteristic of max input frequency up to 1.3 GHz.According to the requirements of phase noise and lock time,the bandwidth and parameters of phase-locked loop filter are optimized and debugged.The experimental results show that the output frequency rang 4.1GHz to 8.1GHz,and the phase noise is better than-116dBc/Hz@lOkHz?-116dBc/Hz@100kHz?-114dBc/Hz@1MHz.(4)The DDS frequency source is integrated with the C-band phase-locked loop frequency synthesizer.In this paper,the output signal of the DDS frequency source is used as the reference signal of the PLL frequency synthesizer,and the C-band frequency synthesizer with ultra-wideband,small step frequency and fast scan is fabricated.The experimental results show that the output frequency rang 4.1GHz to 8.1 GHz,the sweep period is 20ms and the phase noise is better than-110dBc/Hz@10kHz?116dBc/Hz@100kHz.The broadband frequency synthesizer developed in this paper has the characteristics of low phase noise,high spurious rejection,miniaturization,low cost and simple circuit design,and it can be widely used in a FMCW millimeter wave radar system.The frequency source is also suitable for use in other broadband microwave millimeter wave launch system,broadband receivers,measuring instruments and other broadband electronic systems.