Antennas: Type of antennas

ANTENNAS: TYPE OF ANTENNAS

Definition: 

An antenna is a structure that is generally metallic object, often a wire or group of wire used to convert the high-frequency current into electromagnetic waves, and vice-versa

Type of antennas:

1) Omni-directional antennas:

 Omni-directional antennas propagate the radio wave signal in all horizontal directions.

 Dipole antennas:
This is the type of the omnidirectional antenna whose propagating radio frequency (RF) energy in 360 degrees in the horizontal plane. This antenna can be as simple as two pieces of wire cut to the proper length or can be encapsulated. An antenna exhibits a typical impedance, allowing antenna of the transmitter for maximum power transfer.
Majority of the wireless access points and routers have these wireless antennas due to their reliable performance and uniform coverage.
Example of omnidirectional antennas is Rubber duck Omni Directional Antenna

2)Semi-directional antennas:

Semi-directional antennas propagate a radio wave in a restricted area, defined by a specific angle.

Patch antenna:
A patch antenna is a semi-directional radiator using a flat metal strip mounted above a ground plane. Radiation from the back of the antenna is effectively cut off by the ground plane, enhancing forward directionality.  This type is manufactured by standard printed circuit board methods. Patch antennas are widely used semi-directionals; a patch antenna can have a typical gain of 9 dB. This type of the antenna is commonly used in mobile communication.
Example of the patch antenna is Microwave antennas.
Sector antenna:
Sector antennas are another type of semi-directional antenna. Sector antennas provide a pie-shaped (sector) radiation pattern and are usually installed in what is known as a sectorized array. Sector antennas cover the area of the 180 more or less than it.  Sector antennas are used extensively for cellular communication.

 3)Directional antennas: 

Directional antennas use a narrow “beam” of the radio signal that allows highly directional propagation.

Yagi antenna:
 A Yagi antenna uses several elements to form a directional array. A single driven element, typically a dipole, propagates RF energy; placed immediately in front of and behind the driven element re-radiate RF energy in phase and out of phase, enhancing and retarding the signal, respectively. The elements are called parasitic elements; the element behind the driven element is called the reflector, while the elements in front of the driven element are called directors. Yagi antennas have beamwidths in the range of 30 to 80 degrees and can provide a gain of 10 dB.

Parabolic antenna:
A parabola is a symmetric curve; a parabolic reflector is a surface that describes that curve throughout a 360-degree rotation—a dish or, to use the technical term, a paraboloid. A parabolic reflector has a high degree of directivity and has the ability to focus RF energy into a beam, much like a flashlight. Parabolic antennas have a very narrow beamwidth, usually not exceeding 25 degrees. Gain is dependent on diameter and frequency. Parabolic antennas are used for long-distance communication links between buildings or over large geographic areas.

Grid antenna:
This type of the antennas is just similar to the parabolic antennas, but instead of the plane surface grid structure is used. The spacing of the grid elements is frequency dependent; it is inversely proportional to the frequency. Gain and bandwidth are similar to the parabolic antenna.