Antennas have been used for many years and together with technology, they also evolved into different types to fit each of the applications they were designed for. Antennas are generally classified on the basis of frequency, aperture, polarization and radiation. Here, we take a look at these classifications and what their uses are:



Frequency Basis


Antennas classified according to their frequency include very low frequency (VLF), low frequency (LF), medium frequency (MF), high frequency (HF), very high frequency (VHF), super high frequency (SHF) and extremely high frequency (EHF) antennas.


This classification is based on the frequency band capability of each antenna. For instance, a VLF antenna transmits 3-30 KHz and is used for navigation and SONAR, the MF antenna transmits 300-3000 KHz perfect for AM broadcasting and the EHF antenna transmits 30-300 GHz making it ideal for RADAR and experimental uses.



Aperture Basis


Apertures antennas include wire, horn, parabolic and cassegrain varieties that transmit and receive energy from its aperture. The wire antenna is the most common type because its mechanism is simple and it’s relatively cheap compared to other antennas.



A horn antenna is shaped like a conical horn and commonly used as a waveguide where it radiates radiation into an open space. Also called as a microwave dish, the parabolic reflector antenna has a three-dimensional curved surface. The cassegrain antenna, on the other hand, is used because it has better beam steering capacity, is less prone to back scatter and has the ability to place a feed in a good location.



Polarization Basis


Linearly polarized and circularly polarized antennas are classified depending on the polarization of their electromagnetic waves. Antennas transmitting or receiving E field vectors either horizontally or vertically are classified as linear while those who transmit or received E field vectors in any orientation are known as circular.



Radiation Basis


Antennas classified on the basis of their radiation pattern include directional, omnidirectional, isotropic and hemispherical antennas. Also known as a unipole, an isotropic antenna radiates uniformly in every direction, but it is fictitious and used only as a reference antenna. An omnidirectional antenna will radiate well in in azimuth direction, which all wire antennas have in common.



A directional antenna, on the other hand radiates energy only in one direction. This makes it ideal for covering a large wireless distance because of its high gain. A log periodic antenna is the perfect example of the directional type. Finally, a hemispherical antenna radiates on either the upper or lower hemisphere. Hemispherical antennas are commonly used in aircrafts to radiate data from the lower hemisphere.




These are just four of the many factors that designers take into account when designing an antenna for a specific application. Other things that should be considered include antenna efficiency, gain, beam area, radiation resistance and antenna measurements, all to ensure that the antenna achieves its purpose.



This is why it’s very important to find a company with designers who have a good understanding of these principles to make sure that your antenna is really worth your investment.




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