Antenna Theory Fundamentals
A receiving antenna captures electromagnetic radiation in the form of radio, television or wireless telephone signals. At a distance from the receiving antenna — such as a radio or television station — the original sounds and/or images are transformed into electrical signals and are sent out via a transmitting antenna. This is the opposite of a receiving antenna, although the two may look identical.
Depending on the frequency of the signal you’re sending or receiving and other factors such as the direction, height and power of both the transmitting and receiving antennas, the size, shape, and design of your antenna will need to be adjusted for maximum performance. For a simple example of this phenomenon, think of the two different antennas a typical AM/FM radio utilizes. For FM broadcast reception in the 88 to 108 MHz frequency range, most radios come equipped with an externally mounted telescoping rod antenna that swivels to best capture a FM station. However, the antenna used for AM broadcast reception in the 540 kHz to 1.705 MHz frequency range is usually an internally located ferrite rod with a thin wire wound around it.
The basic idea is that the design of an antenna is influenced by the signal it’s meant to receive.
Common Antenna Theories
To gain a better understanding of antenna design, it’s helpful to be aware of the following common antenna properties and theories.
- Directivity: A fundamental property to take into consideration in antenna design is the antenna’s directivity — or the measurement of how directed its radiation pattern is. An omnidirectional antenna would, in theory, have zero directionality, while an antenna that sends or receives signals focused in one direction would have higher directivity. Typically, smaller electrical antennas like dipole antennas have lower directivity. For antennas with high directivity, think of those that are several wavelengths in size, like satellite or horn antennas.
- 3DBF: Three-dimensional beamforming — or 3DBF — is a method by which both elevation and azimuth are considered when sending or receiving a signal to ensure the best angle of arrival. In dynamic 3DBF, broadcast signal antennas are automatically tilted to the intended user’s location.
- Antenna gain: Antenna gain indicates the strength of a signal that an antenna sends or receives in a particular direction when compared to an ideal antenna in hypothetically the same situation. For a television antenna where you know the signal’s originating direction, you would want an antenna with high gain. However, for a mobile GPS antenna that could be connecting to any number of satellites, you would want an antenna with relatively low gain.
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