Antennas: Assignment 11:

1. For a Yagi-Uda antenna, if number of directors keep on increasing then the gain of the antenna: 

Increases

Decreases

Remains nearly constant 

First increases and then saturates

Ans: a

        

Common Data for Questions 2-5: A 3-element Yagi-Uda antenna is designed for GSM1800 using wire diameter of 5 mm.

2. The approximate lengths of reflector, driven, and director elements are respectively:

7 cm, 7.5 cm, 8 cm

7 cm, 8 cm, 7.5 cm

8 cm, 7 cm, 7.5 cm

8 cm, 7.5 cm, 7cm

Ans: d

3. The approximate spacing between driven and reflector elements in cm is:

3

3.75

4.5

5.8

Ans: b

4. The approximate spacing between driven and director elements in cm is:

3.75

4.5

5.8

7.5

Ans: c

5. The maximum gain achieved using a 3-element Yagi-Uda antenna is approximately:

3 dBi

5 dBi

7 dBi

12 dBi

Ans: c

6. The radiation patterns of Yagi-Uda and Log-Periodic antennas are respectively: 

Broadside, Broadside

Broadside, Endfire

Endfire, Broadside

Endfire, Endfire

Ans: d

7. A Log-Periodic antenna provides ________ gain and __________ bandwidth as compared to Yagi-Uda antenna.

Higher, Larger

Higher, Smaller

Lower, Larger

Lower, Smaller

Ans: c      

 

Common Data for Questions 8-10: A Log-Periodic antenna is designed to operate in the frequency range of 400 MHz to 700 MHz for a gain of 8 dBi. The optimum values of τ and s are approximately equal to 0.865 and 0.16, respectively. The diameter of the dipole elements is 5 mm.

8. The minimum number of dipole elements required is:

4

5

6

7

Ans: b

  

9. The lengths of the largest and the smallest dipole (in cm) are: 

37.50, 18.16

37.50, 20.99

32.81, 18.16

32.81, 20.99

 Ans: b

10. The total length of the antenna in cm is: 

52.15

46.34

39.63

26.33               

Ans: b