An antenna is:  (NOTE: More than one answer)Select one or more:a.none of the aboveb.a mechanical transducer that converts sound wave to the electromagnetic wavesc.a transducer that converts free space wave to a guided wave in transmission mode and guided wave to free space wave in reception moded.a transducer that converts free space wave to a guided wave in reception mode and guided wave to free space wave in transmission modee.a spatial filter that have a directional propertyf.has definite polarisation that must be considered in design and test

The correct answers are:

c. An antenna is a transducer that converts free space wave to a guided wave in transmission mode and guided wave to free space wave in reception mode

d. An antenna is a transducer that converts free space wave to a guided wave in reception mode and guided wave to free space wave in transmission mode

e. An antenna is a spatial filter that has a directional property

f. An antenna has definite polarization that must be considered in design and test

Here's why:

a. "None of the above" is not correct because there are correct answers in the options.

b. An antenna is not a mechanical transducer that converts sound waves to electromagnetic waves. This is a description of a microphone, not an antenna.

c. & d. An antenna is a transducer that converts free space waves to guided waves and vice versa. In transmission mode, it converts guided waves (electrical signals in a transmission line) into free space waves (electromagnetic waves in the air). In reception mode, it does the opposite.

e. An antenna acts as a spatial filter because it has a directional property. This means it can transmit or receive signals more effectively in some directions than in others.

f. An antenna has a definite polarization, which is the orientation of the electric field of the radio waves it transmits or receives. This must be considered in the design and testing of the antenna because it affects the antenna's performance.