Design And Implementation Of Frequency Source Of RF Module For K-Band Communication System

At present,wireless communication is developing towards higher communication frequency,larger channel capacity,and higher information transmission rate.Its urgent development needs and increasingly scarce spectrum resources have prompted researchers and engineers of RF systems to focus on higher frequency bands.K-band microwave signals have high frequency and short wavelength,and are widely used in military,satellite and other communication systems.The RF module of this project is designed to meet the needs of a K-band communication device.The frequency source module is a core component of various electronic devices and communication systems,and its performance seriously affects the upper limit of the whole system performance.Based on the requirements of the RF module of the K-band communication system,this paper designs and implements a frequency source that can output the L-band and K-band local oscillator signals satisfying the superheterodyne secondary frequency conversion structure.First at all,this paper introduces the development,classification and research status of frequency synthesis technology.Then introduces the basic structure of the PLL and the principle and working mode of each component,and analyzes the characteristics of phase transmission,locking and stability of the PLL in working conditions,and introduces the source and composition of the noise in PLL.Based on the analysis and calculation of noise,the scheme to reduce phase noise is proposed and the determination of the optimal loop bandwidth is deduced.Secondly,according to the project requirements,the structure of the RF module was designed and the index of the frequency source were determined.The frequency source will output an X-band signal with a PLL,and then obtain a K-band signal and an L-band signal through the frequency-doubled branch and the frequency-divided branch respectively as a two-stage local oscillator signal of the transceiver link of the RF module.According to the index and structure of the frequency source,appropriate chips are selected to build each module of the circuit,and then the optimal loop bandwidth is determined according to the performance of the reference crystal oscillator and the VCO chip.Based on this,an active loop filter constructed by triode and capacitor resistance is designed,its loop transmission performance is deduced and the parameters of each element are calculated by using MATLAB.A three-way power splitter connected with a PLL,a frequency-doubled branch and a frequency-divided branch is designed.Through repeated adjustment and simulation,it meets the requirements of input and output power of each chip to ensure that the frequency source can work normally.After completing the complete design of each module of the frequency source,the PCB board is drawn,the physical object is fabricated and the welding and debugging are completed.After actual testing,in the two output ports of the frequency source,the phase noise of the 1.5 GHz signal output from the L-band port reaches-106.922dBc/Hz@1KHz,-111.890dBc/Hz@10KHz;the phase noise of the 24 GHz signal output by the K-band port reaches-82.177dBc/Hz@1KHz,-87.488Bc/Hz@10KHz.At the same time,the power,frequency accuracy,harmonic spur suppression,phase noise and other indicators of each output signal meet the design requirements.