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161_1_final_2005_solution

161_1_final_2005_solution - EEIGI Final Exam Name Score...

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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 . H) St :: jag-D : #23. D ,MLpe/Q Dz/I- firJ/{W [fip‘gp St = :35; => acme, >0<ZJZ 49(0- -'~—a M“ F“ i! .u, mu h. v \ 3 4;, ‘5. % if u Name: \\ Grade: 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 half-wave 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;”: ' (his; - A; I : among _1_ r”; 0 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?’X5-30k.)(fijc Name: Grade: Problem #5. (20 Points) A linear array arranged along the Z-axis 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 (x-y 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 half-wave 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%) / Z lira) : g 6‘7 / " \ /0fi'a:)72 —I- air/t? F3k¢fw0*3_ Xrl’mdm = brim“ MK. fimofs‘m :32 W e/W gen £1? HW‘EEE ((9: f ) Xaliéafifm gramgfio Dl/V, 73m marry «a, mu W ...
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