ECE 6130 Impedance Matching Text Sections: 5-2 Portfolio question: How do you design a single-stub matching network for "any" complex load? Examples: ECE315 text Chapter 2 (available on reserve in library or in the IEEE room) Problems 35,36,38 (single stub matching) IMPEDANCE MATCHING: A matching network is used so that there is no reflection from the load to the generator. (Zin (at input to matching network) = Zo) One way to do this: Quarter-Wave Transformer Disadvantage of 1/4 wave transformer? We must be able to adjust both L and Zo (size/shape of TL). This is not easy. Better method: (Single Stub Matching) Use a known transmission line short or open-circuited at the end (a stub). Control the length of the stub and the distance to the load (both easy to control). How to model stubs: Equivalent circuit at junction M-M':Yin = Ys + Yd EXAMPLE (See transparencies) Matching: For matched system, Yin = Yo This is accomplished by: Adjusting the line length (d) until Yin = Yo ± jX and then adding in a capacitive / inductive component (short-circuited stub) to remove X. Single-Stub Matching: 1) Plot zL 2) Reflect it through the origin to find yL 3) Rotate yL towards the generator until it reaches rL = 1.0 circle (there will be two points, choose the closest one). This is the length (d) between the load and the stub. 4) Read the value of xL 5) For a short-circuited line, Plot zL (left hand side), and reflect it through the origin to yL (right hand side) 6) Rotate the short-circuit towards the generator until it reaches ys = 0 - j xL. This is the length of the stub. 7) The new yin = 1 + j0 (bull's-eye) EXAMPLE (see
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