推 ketsu1109 :已收入精華區 01/10 14:01
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%)
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※ 編輯: gwava 來自: 61.217.214.106 (01/09 22:29)