Antennas

An Antenna acts as a

• Generator

• Transducer

• Transceiver

• Transition device

A wire can act as an antenna

• When Powered with AC

• When Powered with DC

• When it is bent

• When it is covered

Which one of these has the lowest beam width?

• Isotropic Antenna

• Full Wave Dipole

• Half Wave Dipole

• Yagi Uda Antenna

For VSWR to reach zero, the circuit should be

• Open Circuited

• Short Circuited

Choose the incorrect statement

• The current distribution of a very short dipole would nearly look triangular

• The current distribution of a short dipole would nearly look triangular

• The current distribution of a short dipole would nearly look uniform

• The current distribution of a very short dipole would nearly look uniform

Choose the correct statement

• In a radiation pattern drawn for an antenna, the distance in any direction is inversely proportional to the field strength.

• An isotropic antenna radiates equally in all directions

• A half-wave dipole is an omnidirectional antenna

• In a radiation pattern drawn for an antenna, the distance in any direction is directly proportional to the field strength.

Choose the correct statements

• We can observe spherical wave fronts in the far-field of an antenna

• We can observe plane wave fronts in the far-field of an antenna

• If the distance from the antenna is greater than $\frac{2D^2}{\pi}$ , we are in the far field of that antenna

• If the distance from the antenna is smaller than $\frac{2D^2}{\lambda}$ , we are in the near field of that antenna

As the length of the dipole increases,

• The HPBW decreases

• The gain decreases

• The directivity increases

• Minor lobes appear

• Number of nulls in the radiation pattern decreases

If $\theta_{HP\ }=78^0$ and  $\phi_{HP}=360^0$  , what is the directivity in dB?

• 1.04 dB

• 1.67 dB

• 3.87 dB

The theoretical approach to increase the directivity in a Yagi Uda antenna,

• increasing the number of directors

• decreasing the number of reflectors

• increasing the number of reflectors

• Decrease the space between elements