161_1_MT2_soln

161_1_MT2_soln - EE161 Midterm #2 Solutions (Fall 2006) 1....

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Unformatted text preview: EE161 Midterm #2 Solutions (Fall 2006) 1. In this problem, we use the microstrip as a quarter wavelength transformer to match the impedance of a coax line to a resistive load. (a) The characteristic impedance of the coax line is Z coax = ln b a 2 = r ln b a 2 = 120 2 . 25 ln 1 . 75 . 5 2 = 50 . 11 (b) Parallel plate waveguide model is used to analyze the microstrip impedance trans- former, therefore, the dominant mode is TEM mode. = k = = 2 f r C = 2 3 10 9 10 . 3 3 10 8 = 201 . 65 rad / m u p = = = C r = 3 10 8 10 . 3 = 9 . 35 10 8 m / s g = 2 = 2 201 . 65 = 3 . 12 cm (c) The microstrip works as a quarter wavelength transformer, therefore, L = g 4 = 3 . 12cm 4 = 7 . 8 mm Z ms = radicalbig Z L Z coax = 18 50 . 11 = 30 . 03 Z ms = t r W = 120 10- 3 10 . 3 W = 30 . 03 W = 3 . 91 mm 2. 5GHz is the cutoff frequency of the dominant mode.2....
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161_1_MT2_soln - EE161 Midterm #2 Solutions (Fall 2006) 1....

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