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EE262 Midterm, 2013
Name:_______________
Problem 1. (25 pts) Please determine if the following statements
are true or false and
provide a few sentences to support your judgment.
(a)A monopole antenna will have the same directivity but half of
the radiation
impedance of a dipoleFalse, a monopole antenna has twice the
directivity of that of a dipole
(b)The reason that folded half-wave dipole exhibits a higher
input impedance is
because both the common mode and the difference mode are
radiatingFalse, the difference mode is not radiating and it just
helps with the impedance
match
(c)
With the same aperture size, an E-plane horn provides an lower
directivity andhigher sidelobes than an H-plane horn
False, the E-plane horn has an higher directivity than that of
the H-plane horn due toits uniform amplitude distribution in its
opening over the sinusoid distribution of the
H-plane horn
(d)The plane wave expansion assumed in the spectral domain
method can notrepresent the near field of an antenna as the near
field is not propagating
False, plane wave expansion includes the evanescent waves which
can represent thenear field
(e)According to equivalence principle, current flowing on a
conductor surface does
not radiateFalse, current flowing on a conductor is the main
mechanism how radiation is formed.
Equivalence principle means an impressed (external) current
drawing near to aconductor does not radiate due to the cancellation
of radiation from the induced
current on the conductor
(f)In the input impedance plot of a microstrip patch antenna,
zero reactanceindicates the physics that no energy stored in the
antenna at that frequency
False, zero reactance means the stored electric energy is of the
same amount as thatof the stored magnetic energy
(g)
The radiation characteristics of probe fed microstrip antenna is
generally
different from a monopole antenna that is loaded with flat hat
on top even thoughthey have basically the same physical
structure
True, the probe fed microstrip antenna supports a TM010 mode
while the monopoleoperates more like the TM0.5,00 mode
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Problem 2. (25pts) A thin slot on a conducting plane has a
uniform aperture field
distribution and with a length of 5mm and a width of 0.5mm. If
it is used as atransmitting antenna at 60GHz, please estimate (1)
how much power will be transmitted
out of this slot if the aperture voltage is 1V. (2) how much
susceptive energy will be
stored in such a slot. (3) the value of either an external shunt
inductor or capacitor if it isused to make the antenna resonate.
(4) the quality factor of such an antenna underresonance
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Problem 3. (25pts) A linearly polarized pyramidal horn antenna
is used with a transmitterin a microwave communication system
operating at 10GHz. The pyramidal horn has been
designed for optimum gain. The dimensions of the horn at the
aperture are 5!0by 3!0.
The total output power of the transmitter is 100Watt. The
antenna has a radiationefficiency of 95% and at the input of the
antenna the reflection coefficient is -15dB.
Determine: (a) the maximum directivity and maximum gain of the
horn (b) Maximumpower that can be received by a half-wave dipole
antenna at the distance of 10Km. (c) If
a lens is used to correct the phase error completely on the
aperture, the reflectioncoefficient increases to -7dB, redo the
questions in (a) and (c)
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Problem 4. (25pts) An inset fed rectangular microstrip patch
antenna is shown in the
following figure. The dielectric constant is 2.2. Assuming the
width of the feedline isW0=0.2984cm and the height of the substrate
is h=0.1575cm. Other dimensions include
W1=0.4cm, W2=1.2cm and L=1cm. If we ignore the discontinuity
effect cause by the
feeding, (1) find out the first resonant frequency of this
antenna (hint: total effectivelength should be about !/2) (2) If
the input impedance at its leading radiating edge is
120Ohm, at what distance L1should the microstrip patch antenna
be fed so as to have aperfect match between the line and the
radiating element? (3) Sketch the radiating pattern
of the antenna in E-plane and H-plane in the polar plot.
L1
L
W2
W
1
W
1
W
0
