4 Characteristics That Differentiate Antennas
There are many types of antennas depending upon the application.
When selecting an antenna for a particular application, certain factors should be considered. Here are the four main factors that differentiate commonly used antennas:
Frequency – Electromagnetic waves of a wide range of frequencies are used for communication. Different names are given to electromagnetic signals at different frequency ranges.
When selecting an antenna, the range of frequencies that will be transmitted or received as well as their bandwidth should be considered. Some antennas are designed to operate over a narrow range of frequencies while other antennas are designed to operate over a broader band of frequencies.
Wire-like antennas, for example, are used for signals roughly in the frequency range 3 kHz?f?3 GHz3 kHz?f?3 GHz. Solid cone, platelike, or aperture antennas are used to transmit and receive signals in the frequency range 3 GHz?f?3 THz3 GHz?f?3 THz.
Impedance – In the electrical context, impedance is defined as the ratio of voltage to current (or electrical field strength to magnetic field strength), and it is measured in units of ohms (Ω). At zero frequency, that is, when the current involved is a direct current, both voltage and current are expressible as real numbers.
Impedance matching is a fundamental aspect of RF design and testing.
Directivity – Antennas can be designed to radiate energy equally in all directions or in a single direction. An antenna which radiates equally in all directions is called isotropic. An antenna that radiates equally in two, but not the third, direction is called omnidirectional.
Electromagnetic Polarization – Antennas may be designed to transmit linearly, circularly, or elliptically polarized signals. Antennas designed to transmit or receive circularly polarized signals often contain wires that coil in the corresponding direction around an axis.
If a signal is transmitted with an antenna designed to transmit linearly polarized waves, the best antenna to use as a receiver will be one that is also designed for linearly polarized waves.
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