- 2075 Baisakh · 2+2 marks
What is an antenna; its properties
Short answer
An antenna is a transducer that converts guided electrical signals to radiated electromagnetic waves and vice versa. Directivity is the ratio of radiation intensity in the best direction to the average intensity; gain equals efficiency times directivity. The radiation pattern plots field strength versus direction, showing directional or omnidirectional behavior.
What is an antenna? Explain any two properties of the antenna.
An antenna is a transducer that converts an electrical signal on a transmission line into an electromagnetic wave radiated into space (transmitting), and converts a received electromagnetic wave back into an electrical signal (receiving). Examples: dipole, monopole, loop, Yagi-Uda, parabolic dish.
Two important properties
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Directivity and gain:
- Directivity is the ratio of the radiation intensity in the best direction to the average radiation intensity over all directions.
- Gain = efficiency × directivity, usually in dB relative to an isotropic radiator (dBi). A high-gain antenna radiates strongly in one direction, increasing the range. A half-wave dipole has a gain of 2.15 dBi.
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Radiation pattern:
- It is a graph showing how the radiated field strength varies with direction around the antenna.
- Omnidirectional antennas (a vertical monopole) radiate equally in the horizontal plane; directional antennas (Yagi-Uda, dish) have a main lobe and small side lobes.
Other properties: bandwidth, input impedance, polarization, beamwidth, efficiency.
✓ Answer checked by Claude Opus 5.5 (high effort)
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