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Antennas
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Dipole antennas radiate and receive EM waves.
A half-wave dipole is resonant at length λ/2 and radiates mainly sideways. Larger or directional antennas (Yagi, dishes) focus the power.
FM 100 MHz: dipole length 1.5 m.
Gain describes directionality.
In more detail
An antenna converts electrical signals into electromagnetic waves and back. Its length is typically related to the wavelength, with a half-wave dipole being a common design.
Real-world uses
- Mobile phones and radios use antennas to send and receive signals.
- Satellite dishes and TV aerials are designed for particular frequencies.
- Phones and car radios use dipole antennas, whose length is chosen to match the wavelength of the signal.
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Frequently asked questions
Why are antennas sized to the wavelength?
Resonance is strongest when the antenna length matches a fraction of the wavelength.
What is a dipole antenna?
A straight conductor split in the middle and fed by a transmission line.
Why is antenna length related to wavelength?
An antenna resonates efficiently when its length is a simple fraction of the wavelength, such as a half-wave.
Related topics in AC Circuits & EM Waves
X-rays · Gamma rays · Polarisation of EM waves · Waveguides and transmission lines · Modulation (AM and FM) · Optical fibre communication