| Microwave communication plays an un-replaceable role in military and civilian communication fields. Reducing noise of microwave circuits is a focused problem all the time. The noise of microwave system is ever the central factor that may restrict the system performance increasing from the day when microwave technology was created.Low noise amplifiers are key components of microwave systems. Low noise design is an important content of electronic system, and the origin, character, amount of noise in devices and the noise model of system and devices are the base of low noise design.This dissertation focuses on the computation and measurement of the microwave devices and systems for their noise characteristics, which is the key problem of low noise circuits' design of microwave field and is also an innovative and practical study. I. Study on noise sources of microwave devices and noise models The origins and characteristics of noise sources in microwave devices are investigated in this dissertation. Based on the noise models of microwave circuits, it is researched here like definition, meaning of parameters and applied field about the Rn-Gn noise model, and so on. It laid stress on Rn-Gn noise model and some others derived from Rn-Gn noise model. Most microwave circuits can be regarded as a two-port network or several inner-connected two-port networks in analysis and computation. This method is more concise then the node analysis method and it can use matrix to realize fast computing. In the microwave circuits design process, the noise measurement, computation, analysis and noise parameters extraction based on two-port network is of very practical value in microwave engineering, especially in LNA design.II. Study on noise figure measurement and extraction of noise parameters There are many methods of NF measurement. The comparison were made for speed, accuracy, difficulty and frequency span. Integrating the empirical method from Fukui and the LMS method form Lane, a new method was presented here for noise parameters extraction. For 3 dB method and auto measuring method, two measuring systems are separately built using the two upward methods, and we produce the impedance-tuner, a key part of noise measuring system. And we measured S-parameter of the tuner by HP8714ET, in which reflect parameter can be changed into source impedance. Furthermore, noise figures of microwave amplifiers are measured with HP8970B, a noise figure-measuring instrument, under different source impedances. Moreover, this dissertation studies noise measurement of cascaded networks, which is common in noise parameter measuring, corrects Frris's formula expression under unequal bandwidth (latter bandwidth is bigger than former, and the latter can't be ignored), analyzes the deficiency 3dB method, and improves the point noise figure measuring method.Based on measuring noise figure, noise parameters of noise model are extracted. Owing to the inevitable errors of noise figure measurement, the extracting process involves solving non-linear equations. So noise parameter extracting precisely is very difficult, and IRE's traditional drawing method, Lane's least square method or Fukui's experimentalism method have definite defects and localizations.The new method presented here not only brought the high precision of LMS into play, but also made use of the advantage of Fukui. In order to avoiding errors of choosing source practicable incorrectly, the noise parameters is estimated in advance, such as the optimal source impedances of measured network, and so we can save much measuring time. These working provide a new noise parameters extracting method and procedure, in which we can extract parameters more fast and accurate. NF measurement and extraction for parameters are main work for attaining the noise model.III Caculation method of Rn-Gn noise model for complex circuit networksThis dissertation introduced a connection matrix C for different connecting form. That can slove the noise calculation problem and est...
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