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Unformatted text preview: EEIGI. Final Exam Name:
Score: Problem #1. (20 Points, ABET) A 0.5MHz short dipole antenna carried by a helicopter ﬂying over
the ocean surface generates a wave that approaches the water surface in the form of a normally
incident plane wave. The transmitted power is 3KW. If the height of the ﬂight is about 10 meter
above the ocean and the antenna radiates toward the water in its maximum radiation direction. Seawater is characterized by a, = 72 , p, :1 and a = 4. (I) Find the electric ﬁeld amplitude of the
incident wave right above the water surface. (2) Find the electric ﬁeld amplitude of the transmitted
wave right below the water surface (3) The helicopter is trying to communicate a message to a
submarine submerged at a depth d below the water surface. If the submarine’s receiver requires a minimum electric ﬁeld signal amplitude of 0.1 (pvfm), what is the maximum depth d to which
successﬁil communication is still possible? P .
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Problem #2. (20 Points) Assume that the narrowest strip that can be used reliably as the conductor in 
microstrip line has negligible thickness and a width w=0.lmm. If it lies midway on top of an alumina :
substrate that is 2mm thick, and for which s,=9.8, using parallel plate waveguide model (1) estimate
the highest characteristic impedance attainable. (2) To design 3 M4 transformer at 3GHz frequency,
what will be the physical length of the line? (3) To match a halfwave dipole antenna (ignore the
reactance) to a SOOhm transmission line using this mierostrip impedance Bansformer, what is the
width of the microslrip line? H) Pica/relief wwguﬁoé Mag: 20 3 {If}? A =2rm, 770 = 377le 2r: 38, War»; = amm >me * ptlmm Y (a? ﬂ 240;”: '
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4 ’5’ x 5m”? *3 ‘* 8‘ W“ l Name: Grade: Problem #3. (20 Points) A rectangular waveguide has the dimension a = 5cm and width b = 3cm. (1)
what is the phase constant ,3, guiding wavelength Ag, the phase velocity up and group velocity v: for the dominant mode at 4 GHz. (2) Draw the Hx and H2 field distribution in the waveguide cross
section for the TE” mode. (3) One may make this waveguide an antenna by cutting thin slots on the
top wail. If the slots are small comparing to the waveguide dimension and it has to out across the
maximum surface current flow path in order to create maximum radiation, where shall we cut the
slots and in what orientations? Mark two possible orientations on the corresponding positions on the
top wall. Name: _—__ . Grade: Problem #4. (20 Points) In a wireless communication link, tivo rectangular aperture antennas as
shown In follows have physical areas of l m2 and 1.5 m‘l‘1 and the ﬁeld distribution 1s normal tapering
They are 2000 km apart. Assume all the components are properly matched and the antennas are
properly aligned to get the maximum transmission. The transmitter has a total of 10W transmitth
power. The receiver has a noise temperature of 530K and it needs at least 20dB signal to noise ratio
in order to receive the information correctly. The carrier frequency is 300MHz. (l) Neglecting any
antenna loss, what are the gains of the antennas at this ﬁequency. (2) What is the maximum
bandwidth of the information that the receiver can receive correctly? (3) If only the carrier frequency
is changed to 600m from the previous case, how much bandwidth of the information the receiver can receive now? Transmitting Receiving 3131611113 antenna bales! 571s ﬁrewall . A. 2.
{2) PT :ﬁzﬁtﬁ'r ( 413 ) PM = L’Téf —' /\58X{0‘l?’X530k.)(ﬁjc Name: Grade: Problem #5. (20 Points) A linear array arranged along the Zaxis consists of 10 equally spaced elements with d =£ . (1) Choose an appropriate incremental phase delay 6' so as to steer the main 2
beam to a direction 30 degree above the broadside (xy plane) of the array and provide an expression
for the array factor. (2) Can you estimate the 3dB beam width of this array' in 8 plane, assuming
uniform amplitude and phase excitation and isotropic element pattern? (hint: use aperture antenna formula with no tapering) (3) If halfwave dipole antennas are used for this array and they are aligned
in parallel like in the following ﬁgure with half wavelength spacing. Under the same excitation
conditions as (2), what is the maximum directivity in the broadside of both the array and the antenna? Ty ”DWW x 9 'I’UMdarQ—5) a Shh/0%)
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 Spring '08
 HUFFAKER

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