Antennas are indispensable components for mobile devices and networks. Even though they are located in smartphones and thus hardly visible from the outside, they have a decisive influence on the performance of mobile data transmission. Different types of antennas are used, depending on the area of application, whether in the end device or the base station of the mobile network. In the following article, you will discover how an antenna basically functions, what are the different versions available and the purposes for which these are used.
The functional principle of an antenna
The task of an antenna is to emit electromagnetic waves into the open space or receive them from the open space. The antenna is responsible for the conversion between the open space waves and conducted electromagnetic waves. Practically, it forms the interface between the sender or receiver and the transmission medium of open space. From an electro-technical point of view, an antenna is an oscillating circuit with a capacitative (capacitor) and inductive component (coil) that has a certain resonant frequency. In the oscillating circuit, the energy goes back and forth between the coil and capacitor, alternately generating an electric and magnetic field. To realize an antenna, the oscillating circuit is supplied with conducted electrical energy on one side. On the other side, the oscillating circuit is open, emitting electromagnetic energy into space or absorbing it from the respective space. With this operating principle, a simple dipole antenna can be realized with just two poles.
Classification of antenna types according to emission pattern
Depending on antenna parameters, such as polarization, antenna impedance, degree of efficiency, antenna gain, polar pattern or bandwidth, there are countless different types of antennas. The emission pattern is an important classification criterion when it comes to antenna types. Starting with an idealized ball emitter, also known as isotropic radiator or point radiator, which emits uniformly in all spatial directions, one can make the difference between omnidirectional radiators and directional radiators. The round reflector antenna belongs to the omnidirectional radiators, transmitting or receiving electromagnetic waves in horizontal direction circularly. A typical omnidirectional antenna is the rod antenna. It has a length of Lambda/4 (one quarter of the wavelength) and emits or receives at a 90-degrees angle to the antenna axis, on a horizontal direction, uniformly at 360 degrees.
Directional antennas achieve an antenna gain pertaining to an ideal isotropic radiator in a given spatial direction. Directional antennas include: dipole antennas, parabolic antennas, Yagi antennas or sectional antennas. The directional effect depends significantly on the type of antenna. While sectional antennas are optimized for an emission radius of 120 degrees, for example, a directional antenna or a parabolic antenna achieves a significantly higher directivity at a smaller angle and must be precisely aligned with a remote station.
Use of various antenna types in mobile communications
Depending on the area of application, mobile communications antennas present significant differences in their design and characteristics. For end devices such as smartphones, omnidirectional antennas are normally used. This is because the devices should be supplied in a reliable manner with radio signals from all directions in the available space, regardless of their orientation. The base stations of a mobile network, on the other hand, are equipped with directional sectional antennas. Usually, three antennas with an emission direction of 120 degrees are sectionally arranged on the radio mast, which together provide a coverage of 360 degrees to the radio cell. The horizontal emission direction is slightly tilted downwards, in order to achieve an improved delimitation from neighboring radio cells.
When it comes to point-to-point connections of the base stations with the core network of the mobile communications provider, directional antennas can be used, if the wired coverage is not possible or the associated costs are too high. Distances of many kilometers can be bridged through these radio links.
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