Research And Implementation Of Wideband High Resolution Frequency Synthesizer

Microwave pulse signal is widely used in electronic countermeasures,pulse radar,medical imaging,high-power microwave countermeasures and related effects.In the microwave-induced thermo-acoustic tomography systems,the pulse width of microwave pulse signal is the most important factor to determine the imaging resolution.In the study of high power microwave effect,narrow pulse signal with high isolation has practical application value.However,in the market,the price of microwave narrow pulse modulation source with pulse width less than 10 ns is still very expensive,and the isolation and modulation waveform are not ideal.In this application background,the narrow pulse modulation technology based on diode modulation is studied in this paper.Two kinds of broadband microwave narrow pulse modulators with small size,low price and convenient application are designed,and combined with phase-locked microwave source to obtain broadband and high isolation narrow pulse signal.The research work of this paper is mainly divided into the following parts:Firstly,this paper analyzes the basic principle of microwave narrow pulse modulator,and the problems of microwave switch based on PIN diode in the process of pulse modulation,such as switching time,pulse waveform distortion and insufficient isolation.Therefore,the design schemes of cascaded microwave pulse modulator based on Schottky diode and broadband microwave narrow pulse modulator with double balanced structure are proposed.Then,the circuit principle of the diode cascaded pulse modulator is simulated by using the electromagnetic simulation software ads,and the field-circuit co-simulation is carried out by combining with the HFSS full electromagnetic simulation software to improve the accuracy of the simulation results.The modulator cavity is improved by the method of field-circuit co-simulation,which effectively improves the spatial coupling and improves the isolation of the modulator.In order to reduce the parasitic parameters generated by lumped parameter devices,distributed components such as spiral inductors and microstrip high-pass filters are used to design the bias and ground paths of the modulation port,which effectively improves the bandwidth and pulse envelope waveform of the modulator.Secondly,the method of field-circuit co-simulation is used to design a broadband microwave narrow pulse modulator with a double-balanced structure.Focus on the analysis and design of the broadband balun of the double-balanced circuit.Several typical broadband baluns were designed and their performances were compared.Finally,the microstrip tapered broadband balun was determined as the broadband conversion balun of the double-balanced pulse modulator.In addition,spiral inductance is introduced in the modulation signal injection path and the ground loop,which effectively improves the matching situation of the modulation port and improves the isolation and bandwidth of the modulator.Finally,a broadband microwave source based on phase-locked loop is specially designed,which can stably output continuous wave microwave signal of 2?12GHz as the continuous signal source of microwave modulation source.The two kinds of microwave narrow pulse modulator and microwave phase locked source are processed,and the experimental platform is built for debugging and testing.The test results show that the isolation of microwave pulse generated by diode cascaded narrow pulse modulator is greater than 45 d B,the rise / fall edge is less than 3ns,the repetition frequency is up to 1MHz,and the pulse width is greater than 5ns.In the working frequency range of 2-10 GHz,the pulse isolation of the dual balanced pulse modulator is better than 20 d B,the rise / fall edge is less than 5 ns,the repetition frequency is up to1 MHz,and the pulse width is more than 10 ns.Both pulse modulators show good pulse modulation characteristics.