Microwave Amplifiers I - Microwave Amplifiers Single Stage...

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1 Microwave Amplifiers - Single Stage Design [1] INTRODUCTION We limit this tutorial to single stage transistor amplifiers. Background material covering characteristics of microwave transistors and gain and stability of general two port amplifier circuits can be found in Chapter 11 of [1]. The relevant equations from those sections are reproduced here for completeness. Two-Port Power Gains The three types of power gains for an arbitrary two-port network connected to source and load impedances, Z S and Z L are: Power Gain = G = P L /P in is the ratio of power dissipated in the load Z L to the power delivered to the input of the two-port network. This gain is independent of Z S , although some active circuits are strongly dependent on Z S . Available Gain = G A = P avn /P avs is the ratio of the power available from the two-port network to the power available from the source. This assumes conjugate matching of both the source and the load, and depends on Z S but not Z L . Transducer Power Gain = G T = P L /P avs is the ratio of the power available from the two-port network to the power available from the source. This depends on both Z S and Z L . These definitions differ primarily in the way the source and load are matched to the two-port device; if the input and output are both conjugately matched to the two-port, then the gain is maximized and G = G A = G T . Equations for these gains in terms of the S parameters of the active device and the four different reflection coefficients, shown in Figure 1 and defined below, follow: Figure 1. A Two-port network with general source and load impedances. ( ) ( ) ( ) ( ) ( ) ( ) 2 22 2 2 2 2 21 2 2 11 2 2 21 2 22 2 2 2 21 1 1 1 1 ) 3 ( 1 1 1 ) 2 ( 1 1 1 ) 1 ( L in S L S in L T out S S avs avn A L in L in L S S P P G S S P P G S S P P G Γ Γ Γ Γ Γ = = Γ Γ Γ = = Γ Γ Γ = = where 0 0 0 0 , ) 4 ( Z Z Z Z Z Z Z Z S S S L L L + = Γ + = Γ and
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