What is an Antenna? Classification and Metrics of Antennas

Antenna is a relatively common equipment, widely used in broadcasting, television, radio communications, radar, navigation, electronic countermeasures, remote sensing, radio astronomy and other fields. An antenna is a device that can effectively radiate electromagnetic waves to a particular direction in space or effectively receive electromagnetic waves from a particular direction in space. All wireless devices that transmit signals through electromagnetic waves must have an antenna.

Definition of Antenna: The basic function of an antenna is to radiate and receive radio waves.

Converts high-frequency currents to electromagnetic waves when transmitting.

Converts electrical tidal waves to high-frequency currents when receiving.

Classification of antennas:

Requirements for antennas:

• The antenna should be able to convert as much of the guided wave energy as possible into electromagnetic energy. This requires firstly that the antenna is a good electromagnetic open system, and secondly that the antenna is matched to the transmitter or receiver (which requires calculating or testing the antenna's radiation impedance).

•  The antenna should allow electromagnetic waves to be focused as much as possible in a defined direction, or to maximize the acceptance of incoming waves in a defined direction, i.e., the antenna has directionality (directional function).

• The antenna should be able to transmit or receive electromagnetic waves of a specified polarization, i.e., the antenna has an appropriate polarization.

• The antenna should have sufficient operating frequency band.

  
  

  Common performance metrics for antennas:

• directivity map

• directivity coefficient

• gain

• input impedance

• standing wave coefficient

• efficiency

  
  

  Key factors affecting antenna performance metrics:

  
  

• antenna electrical dimensions

• antenna shape and structure

• current distribution on the antenna

  
  

  
  

  Antennas are both simple and complex:

  
  

Simplicity is generally through simple structures made of metal conductors, such as wires, sheets of metal. Simple antennas are usually monopole (e.g. dipole, monopole vertical antenna, etc.) or unidirectional (e.g. directional antenna). They are simple in structure, easy to manufacture, and are suitable for some basic wireless communication needs, such as home Wi-Fi routers or car radios.

The complexities, as illustrated above, involve obscure fundamental theories of electromagnetic fields, especially in the design of array antennas for radar and satellite communications, which consist of many individual antenna elements and require sophisticated simulation and numerical simulation tools as well as experimental validation.