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ECE 473/TAM 413
Homework Assignment #10
Due: Friday, November 14, 2008
For your information
Hour Exam 2: Thursday, November 20, 2008, 7:008:30 pm, 163 EL
Hour exams are open book (the text for the course) with one sheet of notes (you can use
both sides). Your class notes and lecture notes are not permitted. You can use calculators.
1.
An underwater linear array has 30 elements equally spaced at
d
=
1.5
!
, where
!
is the
wavelength at its operating frequency. (a) Are there any grating lobes? If yes, determine the
angular location of the first grating lobe. (b) Determine the angular width (to the nulls) of the main
lobe of the array. (c) If the main beam of the array is steered 25˚ off the array axis, then determine
the angle of the grating lobe closest to the axis.
2 . The main lobe of a linear array (a line array) is scanned between +60˚ and 40˚. The array
has 40 equally spaced elements, and operates in sea water (c = 1500 m/s;
!
=
1026 kg / m
3
;
13˚C) at a frequency of 1 kHz with an output temporalaverage acoustic power of 10 W.
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 Fall '08
 OBRIAN

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