课程名称︰电磁学二 课程性质︰必修 课程教师︰江简富 开课学院：电资学院 开课系所︰电机系 考试日期（年月日）︰2011/12/13 考试时限（分钟）：2:20 ~ 3:20 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 2011 Fall Electromagnetics II - Quiz II Each problem is 50 points, and the final score will count on the highest 2 scores from 4. Problem 1 For a transmission line of characteristic impedance 50 Ω , terminated by a load impedance (50 + j50)Ω , find the following quantities by using the Smith chart : (a) reflection coefficient at the load ; (b)SWR on the line; (c)the distance of the first voltage minimum of the standing-wave pattern from the load;(d)the line impedance at d=0.15λ;and (f)the location nearest to the load at which the real part of line admittance is euqal to the line characteristic admittance. Problem 2 A transmission line od charateristic impedance 50Ω is terminated by a certain load impedance. It is found that SNR on the line is equal to 4.0 and that first voltage minimum of the standing-wave pattern is located to be a at 0.2λ from the load.Using the Smith chart , determine the location nearest to the load and the length of a short-circuited stun of characteristic impedance 50Ω connected in parallel with the line required to achieve a match between the line and the load. Problem 3 The input impedance of a lossy line of length 50m is measured at a frequency of 200 MHz for two cases : with the output short-circuited,it is (10 + j49)Ω, and with the output open-circuited,it is (10-j49)Ω.Find : (a) the characteristic impedance of the line , (b) the attenuation constant of the line ; and (c) the phase velocity in the line, assumeing its approximate value to be 1.75 X 10^8 m/s. Problem 3 For the lossy transmission line system shown in Fig.1 , fine (a) the time-average power flow at the input end of the line ; (b) the time-average power delivered load; and (c)the time-average power dissipated in the line 9.25λ ←─────────→ ╭╮────────╭╮ ┌─││ ││─┐ │ ╰╯────────╰╯ │ ─ ── ─ ── ─ Z_g=(30-j40)│ │ Z_0=50Ω │ │ Z_R =(30+j40)Ω Ω ── α=0.002NΡ/λ ── ─ │ │ V_g=100V ○ │ │ ╭╮────────╭╮ │ └─││ ││─┘ ╰╯────────╰╯ d=1 ← d=0 Fig. 1 ※ 编辑: nihility7893 来自: 140.112.25.106 (01/16 08:40)