Tutorial 3 - Antenna Arrays

Tutorial 3 - Antenna Arrays - the x-z plane and the x-y...

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1 Tutorial 3 – Antenna Arrays Question 1 A uniform linear array of 20 isotropic elements is placed along the x -axis with an inter- element spacing d = λ /4 and a progressive phase shift of β . Calculate the values of (within the range: - π < ) for the following design: (a) main beam directions at 90° and 270°, (b) main beam direction at 0°, (c) main beam direction at 180°, and (d) main beam direction at 30°. Question 2 The electric field in the far zone of a short dipole ( << A ) carrying a current I 0 and situated at the origin is given by: r e AI E jkr θ 4 sin 0 = where A is a constant. An array is constructed from two such short dipole antennas and placed at a distance d apart with the dipoles laying in the x-z plane as shown below. The current on element #1 is I 0 while that on element #2 is – I 0 . (i) Derive an expression for the array factor |AF n | and draw the array factor for d = /4. (ii) Using the method of pattern multiplication, draw the radiation pattern of the array in
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Unformatted text preview: the x-z plane and the x-y plane for d = /4. Question 3 (a) Two half-wave dipoles are placed along the x axis and with their axes along the z axis as shown below. If the dipoles are fed by currents I and j e I for dipole #1 and #2, respectively, and the separation between them is half wavelength ( d = λ /2), find the normalized array factor for this array in the x-y plane. d #1 #2 x z d = λ /2 y x Dipoles #1 #2 2 (b) Now four half-wave dipoles are placed at the four corners of a square with side length equal to λ /2 as shown in the following figure. The axes of the dipoles are along the z axis. If the dipoles are fed with currents I , 2 π j e I , j e I , and 2 3 j e I for dipole #1, #2, #3, and #4, respectively, find the array factor for this array in the x-y plane. d = λ /2 y x d = λ /2 Dipoles #1 #2 #4 #3...
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Tutorial 3 - Antenna Arrays - the x-z plane and the x-y...

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