- 2073 Magh · 2+4 marks
Types of wired antenna
Short answer
Antenna converts guided EM energy to free-space waves. Wire antenna types include dipole (figure-8 pattern, linear polarization), monopole (omnidirectional, vertical), small loop (figure-8 in plane, linear), long wire (multi-lobe, linear), V/rhombic (directive, horizontal), and helical (end-fire, circular).
Define an antenna. List the various types of wired antenna with their radiation pattern and polarization.
Antenna
An antenna is a metallic structure (transducer) that converts guided electromagnetic energy from a transmission line into free-space electromagnetic waves, and vice versa during reception (IEEE: "a means for radiating or receiving radio waves"). It also matches the line impedance to free-space impedance (377 Ω).
Types of wire antennas
Patterns below are in the plane containing the antenna (E-plane), with the wire drawn vertical unless noted.
| Antenna | Radiation pattern | Polarization |
|---|---|---|
| Short (Hertzian) dipole | Figure-8, max ⊥ wire; omni in H-plane | Linear, along wire |
| Half-wave dipole | Figure-8, slightly narrower (HPBW 78°) | Linear, along wire |
| Folded dipole | Same as λ/2 dipole | Linear |
| Quarter-wave monopole | Upper half of figure-8, omni horizontally | Vertical |
| Small loop | Figure-8 in loop plane; null ⊥ to loop | Linear, in plane of loop |
| Long wire (resonant) | Many lobes; main lobes tilted towards wire | Linear |
| V and rhombic | Directive along bisector/diagonal | Horizontal |
| Helical (axial mode) | End fire along axis | Circular |
| Yagi-Uda, LPDA (wire arrays) | Unidirectional end fire | Linear |
Dipole / monopole Small loop Helix (axial)
| .-. .-. .-. ___
.-. | ( ) ( )O( ) |///| ===>
( )| '-' '-' '-' ‾‾‾
'-' | max in loop plane beam on axis
max ⊥ wire, null on axis null ⊥ loop circular pol.
Long wire (l = several λ) V / rhombic
\ / \ / <V ===>
---------- wire unidirectional
/ \ / \ lobes tilt (terminated)
towards far end
- Dipole antennas suit HF–UHF use (broadcast reception, TV, FM).
- Monopole is used for MF broadcast and mobile whips.
- Loop antennas are used for direction finding and AM receivers.
- Long-wire, V and rhombic are HF travelling-wave antennas.
- Helix gives circular polarization for satellite links.
✓ Answer checked by Claude Opus 5.5 (high effort)
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