Research On Microwave Baseband Frequency Multiplying Technology Based On Coherence Of Signal

With the development of microwave and millimeter wave technology,communication and radar systems for various purposes have emerged very fast.In these systems,signal sources play an extremely important role.So,the signal source become one of the research hotspots in the communication field.In the application of millimeter wave radar systems,the signal source is expected to achieve a wider operating frequency band,which requires the generated baseband signal to have higher frequency and bandwidth.The use of direct digital frequency synthesis(DDS)technology is an important method to achieve wideband baseband signals.However,due to the limitations of DDS chips,the operating frequency and absolute bandwidth often cannot meet the system requirements.Therefore,the spread spectrum technology for baseband signals is very significant.The direct frequency multiplying technique is the simplest and most effective technique for realizing microwave signal spreading.However,when the bandwidth of the microwave signal is very wide,the frequency multiplying process is often interfered by adjacent harmonics.In order to overcome this technical problem,a technical scheme of up-conversion-multiplier-downconversion has been successfully applied.This project deeply analyzed the technical scheme of up-conversion-multiplier-downconversion.For the first time,based on the principle of signal coherence,analyze the influence of the induced auxiliary local oscillator signal during the processing,and compare the phase noise of the input and output signals.The results show that in the up-and-down frequency conversion stream,since the same local oscillator signal is used,the phase noise of the local oscillator source realized coherent cancellation.Therefore,the output signal from the down-conversion will greatly suppress the phase noise of the local oscillator source.The rigorous experimental verification confirmed the correctness of the theoretical analysis.This leads to a crucial conclusion for the engineering designing,that is,the frequency synthesis technology scheme using up-conversion-multiplier-downconversion can effectively avoid the adjacent harmonic interference of the wideband signal in the multiplier,and at the same time the induced auxiliary local oscillator signal is not required to have high spectral quality,thereby the local oscillator signal will not increase the technical difficulty and cost of the scheme.