Assignment 4

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University of Ottawa *

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3106

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Electrical Engineering

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Dec 6, 2023

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docx

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Assignment 4 λ/4 Transformer for Complex Loads University of Ottawa ELG 3106 November 22, 2023
Introduction In this assignment, A λ/4 transformer (see Figure 1) is used to match a line of lossless characteristic impedance Z 01 , with complex load Z L , to a feedline of lossless characteristic impedance, Z 01 . To do that, we need to find the transformer lossless characteristic impedance Z 02 and the load line length d with the help of Smith Chart and simulation app Module 2.7 provided in the textbook website. Theory The input impedance at the source end of a line of length l is given by equation 1 below: Z ¿ = Z 0 { Z L + j Z 0 tan ( βl ) Z 0 + j Z L tan ( βl ) } ( 1 ) In this assignment, we are considering the circuit shown in Figure 1, where Z 01 = Z in , therefore we can use equation 2 to equation the value of Z 02 that is derived by Z in = Z 0 2 /Z L so that we are allowed to find d max and d min to renormalize them to the original transmission line. Z 01 Z ( d ) = Z 02 2 ( 2 ) Figure 1. An in-series λ/4 transformer inserted at either d max or d min
Calculation and Simulation Results Part 1 Given Z 01 = 50Ω, Z L = (100 - j200) Ω, and Z in = Z 01 using Smith Chart, z 01 = (100 – j200)/50 = 2 – j4 Ω, the point is being plotted as point A in Figure 1 below: Figure 2. Smith Chart for d min From the WTG scale, since the closest voltage minimum is at 0λ (point B), d min = z 01 – 0λ, we can see that d min is around 0.218λ, and z(d 1 ) ≈ 0.096. Therefore, by equation 2, Z(d 1 ) = 4.8Ω and Z 02 = [Z in Z(d 1 )] 1/2 = [50(4.8)] 1/2 = 15.49Ω, then we renormalize the line to the original transmission line by plotting the following: z(d 1 ) = 0.096*Z 01 /Z 02 = 0.096 * 50/15.49 = 0.31 as point C, next we draw a SWR circle as shown in
Figure 2 and plot point D to help us to renormalize with Z 01 . Therefore: z in = 3.22 *15.49/50 = 0.998 ≈ 1, renormalized with Z 01 , and Γ = 0.
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