Research On K-Band Broadband Noise Source

Noise source can be used for the interference of the original signal,the pressure damage test of the communication system,the reference level comparison,the fault isolation test of the communication and radar system,the receiver phase tracking and the bandwidth test,the digital conversion error of the high speed converter randomization and other places.At the same time,noise source covers a wide range of frequencies and can improve the efficiency of the test system,so it is very important to study it.Therefore,the K-band broadband noise source is selected for researching in this thesis.In this thesis,the frequency range of the K band broadband noise source is22~32GHz,using noise diode as the core of the noise source device.Compared with the traditional noise sources mainly concentrated in low frequency and narrow band noise output,this thesis will make the output noise signal frequency higher than 22 GHz and realize the broadband noise signal with bandwidth up to 10 GHz and relative bandwidth of 37%.Firstly,the equivalent parameters of the noise diode are extracted.Secondly,the impedance matching of the noise diode is carried out to realize the high flatness and high excess noise ratio output.Finally,the noise source is measured and the uncertainty is analyzed.The whole thesis design is divided into three portions: the design of low noise amplifier circuit,the design of the noise source circuit and parameter extraction of noise diode,the noise diode impedance matching and excess noise ratio measurement.The low noise amplifier circuit is composed of two parts: the power supply circuit with+3.5V and-0.5V voltage and the RF circuit.The noise source circuit is composed of constant current source with constant output current about 15-25 m A,a low-pass filter that provides DC bias,the noise diode and output isolation circuit.When the process and assemblage of the noise source circuit is finished,firstly the parameters11 S of the noise source circuit is measured by the vector network analyzer.Secondly,the corresponding 3D equivalent model of noise source is established in HFSS to simulate the real circuit and the noise diode is replaced by RLC boundary.High frequency equivalent parameters of the noise diode will be obtained through fitting the simulation curve and the measurement curve until they become conformity.To accomplish thenoise diode impedance matching,the noise source HFSS simulation model should be divided into three S2 P files that are necessary in the ADS simulation software.And the matching results in ADS should be imported into HFSS for more sophisticated simulation.The simulation model is imported into AUTOCAD to finish the process and assemblage of the noise source circuit when the impedance matching is finished.Finally,the noise spectrum which is amplified by a low noise amplifier is messured by a spectrum analyzer.The ENR is obtained by equation: PSD(dBm/Hz)=-174dBm/Hz +ENR.After the calculation,the ENR of the output noise signal is greater than 20 dB and its flatness is within ± 2dB.