Antennas

Antennas are structures used to collect or radiate electromagnetic waves. Antennas can be considered specialized transducers that convert RF fields into AC line signals or vice versa. The two main types of antennas are the receiving antenna, which intercepts RF energy and delivers AC to electronic equipment, and the transmitting antenna, which is fed with AC from electronic equipment and generates an RF field.

At frequencies below 3 GHz, many different types of antennas are used such as simple monopole, dipoles, patches or arrays. Dish antennas are generally practical and commonly used at microwave frequencies (above approximately 3 GHz). In wireless data applications, satellite communications and other high bandwidth microwave applications, the most common type of antenna is the dish. Other commonly available antenna styles include omnidirectional, directional, arrays, microstrip, panel, and whips (monopoles).

Omnidirectional antennas radiate equal power in all directions in a horizontal plane.  Conversely, directional antennas radiate their power in either one or two directions.  These are referred to as uni- and bi-directional antennas, respectively.

Arrays are collections of antenna elements (dipoles, slot, loops, and microstrips) that work in concert.   Two of the more common array styles are log periodic and Yagi-Uda.  Log periodic arrays are multi-element, unidirectional, narrow-beam antennas that have impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency.  The length and spacing of the elements of a log periodic antennas increase logarithmically from one end to the other.  Log periodic antennas are often used in broadband applications. Yagi-Uda arrays consist of three or more half-wave elements (one driven, one reflector, and one or more directors).  Yagi antennas or Yagi-Uda arrays offer very high directivity and gain.

Microstrips are typically low efficiency short radiating/receiving antennas, popular for their low profile. Microstrips are easily fabricated with printed circuit board techniques and can be made to conform to most surface profiles.  They can have an unlimited number of shapes and sizes.  When built using special dielectric materials, smaller than natural antennas can be realized that will fit small packages

Panel or sector antennas have multiple antenna elements to radiate or collect signals from different sectors in a cell.  A panel or sector panel antennas usually have a flat panel shape and are usually enclosed within a plastic radome to protect the elements and/or any electronics.  

Whip antennas are flexible rod antennas, usually between 1/10 and 5/8 wavelength long, supported on a base insulator.   These capacitive antennas or electric doublets are insulated from the structure (plane, car or other product) and the whole assembly radiates. The standard, wire monopole is probably the most widely used antenna on existing mobile telecommunication applications with the normal mode helix coming in a close second.

• Dipole Antennas and Wire Antennas
  Dipole antennas or wire antennas are among the simplest and most common type of antennas. They typical configuration for a dipole antenna is a straight, center-fed, one-half wavelength antenna. Often,...
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• Coil Antennas and Helix Antennas
  Coil antennas and helix antennas are designed with the conductor element wrapped or wound around a cylinder, coiled into a flat spiral or in the form of a straight or conical helix. Coil antennas can...
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• Smart Antennas and Adaptive Antennas
  Smart antennas and adaptive antennas have multiple antenna elements to radiate or collect signals from different sectors in a cell. Smart, adaptive or intelligent antenna systems consist of a...
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