Antennas: Assignment 1:

1. The measured half power beam widths (HPBW) of an antenna in the two orthogonal planes are 70° and 65°. The directivity of the antenna in dBi is approximately:

4.8 

 9.6

 19.2

 24.0

Ans: b

2. The normalized E-field pattern of an antenna varies as 0.5(1 + cosθ), where, angle θ is measured from broadside direction. The approx. HPBW of the antenna is:

 131°

 95.6°

 65.5°

 47.8°

Ans: a

3. For a square MSA array, the effective aperture area is 25λ2,  the approximate HPBW in E-plane is:

 36°

 18°

 10°

 5°

Ans: c

4. An electric field vector is given by  E=E1cos(ωt)ax+E2cos(ωt+α)ay. Which one of the following conditions represent right hand circular polarization (RHCP):

E1=E2;α=−π/2

E1=E2;α=0

E1≠E2;α=π/2

E1≠E2;α=0

Ans: a

5. Common Data for Questions 5-6: If reflection coefficient of an antenna is 0.3 at a frequency of 900 MHz, then  The value of voltage standing wave ratio (VSWR) is:

 3

 1.86

 1.5

 1

Ans: b

6. The percentage power transmitted by the antenna is: 

 91%

 80%

 70%

 40% 

Ans: a

7. If input impedance of an antenna is (25 – j25) Ω at 2.45 GHz, the percentage reflected power from the antenna will be:       

 96%

 80%

 20%

 4%

Ans: d

8. A GSM 900 cell tower antenna with 15 dBi gain is transmitting 20 W of power in the frequency band 900 - 905 MHz. The approximate power density at a distance of 100 m in the direction of maximum radiation is:

0.5 milliWatt/meter2

5 milliWatt/meter2

50 milliWatt/meter2

500 milliWatt/meter2

Ans: b

9. Two identical transmitting and receiving antennas are located at a distance of 2 km. If power transmitted is 25 dBm at 10 GHz and received power is -65 dBm, the approximate gain of each antenna in dBi is:

 7.1

 14.2

 17.5

 21.3

Ans: b

10. Transmitting and receiving antennas operating at 2.45 GHz with gains of 15 dBi and 12 dBi, respectively, are separated by a distance of 300 m. If the transmitted power is 2 W, then the received power is approximately:

 10.6 nW

0.1 μW

1.1 μW

10.6 μ W

Ans: c

11. The diameter of a parabolic dish antenna (with efficiency η = 60%) for 40 dBi gain at 10 GHz is:

 123.3 cm

 61.6 cm

 41.1 cm

 30.8 cm

Ans: a