Antennas Practice Test 8

1. If there are no any reflections, then the value of the SWR will be ________________

∞

2. Which of the following modes of radiation, the radiation of helical antenna is along the end-fire direction?

Perpendicular mode

Axial mode

Beam mode and Normal mode

Normal mode

3. What is the frequency of antennas used for Reflection range?

16MHz to 300MHz

3GHz to 30GHz

300MHz to 16GHz

3 MHz to 16MHz

4. In order to get more number of channels in TV reception, we prefer Yagi-Uda than LPDA.

False

True

5. Normal mode of radiation is limited in use because _____

it has broad bandwidth and independent of antenna dimensions

it has narrow bandwidth and dependency on small dimensions of the antenna compared to wavelength

it has broad bandwidth and dependency on large dimensions of the antenna compared to wavelength

it has narrow bandwidth and is independent of antenna dimensions

6. Which of the following is false regarding normal mode of radiation of helical antenna?

The current is assumed to vary along the length of the antenna

The dimensions of the antenna are small compared to the wavelength

The radiation is normal to the direction of the axis

The far field pattern is independent of the number of turns

7. If the spacing between turns of the helical antenna is zero then it acts as a ________

Parabolic antenna

Linear dipole

Log periodic antenna

Loop antenna

8. The empirical formula for the measurement of the high VSWR is give by ____

\(VSWR =\frac{λ_g}{2(d_2-d_1)}\)

\(VSWR =\frac{λ_c}{π(d_2-d_1)}\)

\(VSWR =\frac{λ_g}{π(d_2-d_1)}\)

\(VSWR =\frac{2λ_g}{(d_2-d_1)}\)

9. Find the number of turns in the helical antenna with directivity 120 and C_λ=1 and pitch angle 6°.

120

100

10. What is the antenna efficiency if the gain equals to the directivity of the antenna?