作者gwava (footman)
看板NTU-Exam
标题[试题] 96上 许博文 天线 期中考
时间Fri Jan 9 22:28:27 2009
课程名称︰天线
课程性质:选修
课程教师︰许博文
开课学院:电资学院
开课系所︰电信所
考试日期(年月日)︰2007/11/22
考试时限(分钟):3 hrs
是否需发放奖励金:是
(如未明确表示,则不予发放)
试题 :
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为下标)= 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%)
--
※ 发信站: 批踢踢实业坊(ptt.cc)
◆ From: 61.217.214.106
※ 编辑: gwava 来自: 61.217.214.106 (01/09 22:29)
1F:推 ketsu1109 :已收入 01/10 14:01