Phased Array Written QP4 With Answers.

AQP4

Page 1 of 3 Phased Array Training Question paper 4

Calculate the following settings for this linear array: Frequency: No; of Elements Pitch between elements; Velocity of test material: Passive aperture: K:

1.

7 MHz 128 1mm 5900m/s 12mm 0.5 for –6 dB

Limit of focus depth

Focussing depth limited to near field extent. So near field = D²/4λ

so 16384/4x0.84= 4861mm

AQP4

2.

Page 2 of 3

Width of beam at focus F:

Beam width = Fλ/D

3.

So 4859x0.84/128

Angular beam spread at –6dB in the active aperture far field:

Beam spread formula

Sin θ = λ/D So

Sin θ = 0.84/128 = 0.37°

AQP4

4

Page 3 of 3

Angular beam spread at-6dB for the passive aperture in the far field:

As question 3 but use 12 for the aperture/diameter

So

5.

Sin θ =

0.84/12

Beam spread = 4°

Recalculate the above if only exciting 32 elements. a. b. c. d.

303mm 8mm 1.5° same