課程名稱︰天線 課程性質：選修 課程教師︰許博文 開課學院：電資學院 開課系所︰電信所 考試日期（年月日）︰2007/11/22 考試時限（分鐘）：3 hrs 是否需發放獎勵金：是 （如未明確表示，則不予發放） 試題 : 1. Compute the peak Gain of an antenna which has a radiation efficiency of 95% and the following E-field patter:(15%) E(θ) = 1, 0度 ≦θ≦45度 0, 45度≦θ≦90度 1/2, 90度≦θ≦180度 2. For a center-fed electric dipole with length L = n(λ/2),where n=1,2,3... Plot roughly the polar radiation patterns for n=1,2,3,4,5,and 6,and answer the following question:(20%) (a) Do the lobe maxima increase or decrease monotonically from θ=90度 toward the axis? (b) How many lobes are there, in terms of n, from θ=0度 to θ=180度, if n is odd? (c) How many lobes are there, in terms of n, from θ=0度 to θ=180度, if n is even? (d) Is there a null or a maximum at θ=90度 if n is even and n/2 is even? 3. Prove that a RHCP (right-hand circularly-polarized) wave normally incident on a plane perfect conductor changes to LHCP(left-hand circularly-polarized) upon reflection.(10%) 4. An open-ended coaxial waveguide has the fields in the aperture : Er = A/r, Hψ= A/ηr, for a≦r≦b, where r and ψ are cylindrial coordinates, η is the impedance of free space, and A is a constant. (a) What is the total power radiated by this aperture? (b) Prove , mathematically, that at great distances, the field is zero on the z-axis.(15%) 5. A 1-m long dipole antenna is driven by a 150 MHz source havinga source resistance of 50 ohms and a voltage of 100 V. If the ohmic resistance of the antenna is given by RL(L為下標)= 0.625 ohms, find the following: [Hint: Zant =73+j42.5 Ω for half-wavelength dipole](10%) (a) Current going into the antenna(Iant) (b) Power dissipated by the antenna (c) Power radiated by the antenna (d) Radiation efficiency of the antenna 6. Solve prob. 2.6 in Chater 2 of Elliott's book.(15%) 7. Solve prob. 3.7 in Chapter 3 of Elliott's book.(15%) --

※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 61.217.214.106 ※ 編輯: gwava 來自: 61.217.214.106 (01/09 22:29)