Benha University Antennas &Wave Propagation Electrical Eng. Dept.
Faculty of Engineering 4th year communication
Shoubra 2013-2014
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Sheet (4)
1. Draw the current distribution along a symmetrical dipole made of
infinity thin wire in the following cases
L=0.1λ, L=0.5 λ, L= λ, L=1.5 λ, L=2 λ.
2. Compare the amplitudes of currents that would be required in a half
wave dipole and small dipole of length 0.05 λ to produce 100W of
radiated power from each.
3. A center fed electric dipole of length L is attached to a balanced lossless
transmission line with Zo=50Ω. Assuming the dipole is resonant at L=
λ/50, L=λ/2, Find VSWR.
4. Calculate the 3dB beam width of a wire symmetrical antenna with
length 15m, knowing that the central frequency is 10MHz.
5. For an antenna with a maximum linear dimension of D, find the
boundary of far field region so that the maximum phase error does not
exceed (a) π/16 rad (b) π/4 rad (c) 18o (d) 15o
6. A 3-cm long dipole carries a phasor current I0 = 10 e j60 A. Assuming
that λ =5 cm, determine the E- and H-fields at 10 cm away from the
dipole and at θ = 45o.
7. For an antenna with an overall length l = 5λ, the observations are made
at r = 60λ. Find the errors in phase and amplitude when we use far field
approximation for the distance from the source to the observation point.
8. The boundary of the far-field was selected based on a maximum phase
error of 22.5◦, which occurs at directions of 90 from the axis along the
largest dimension of the antenna.
For an antenna of maximum length of 5λ, what do this maximum phase
error reduces to at an angle of 30◦ from the axis along the length of the
antenna?
Assume that the phase error is totally contributed by the respective first
higher order term that is being neglected in the infinite series expansion
of the distance from the source to the observation point.
Dr. Gehan Sami
Benha University Antennas &Wave Propagation Electrical Eng. Dept.
Faculty of Engineering 4th year communication
Shoubra 2013-2014
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9. A 15 M Hz uniform plane wave having a peak electric field intensity
E0 = 0.05 V/m is incident on a 2.5 λ long dip ole at an angle θ. Assume
lossless dipole
a) Plot the current on the dipole .
b) Find the angles of incidence θ that will give a zero open circuit
voltage Voc at the terminals of the dipole.
c) Plot the far-field E plane pattern of the dipole (Polar plot).
REPORT
1. Draw Elevation plane of radiation pattern for a thin dipole with sinusoidal
current distribution (l = λ/50, λ/4, λ/2, 3λ/4, λ). Determine HPBW for each.
Good Luck
Dr. Gehan Sami
