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Mobile radio antennas – basic operation and different variants

Antennas are indispensable components for mobile devices and networks. Even though they are barely visible from the outside in smartphones, 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 terminal or at the base station of the mobile network. The following article explains how an antenna works in principle, what different variants there are and what they are used for. 

The operating principle of an antenna 

The task of an antenna is to radiate electromagnetic waves into free space or to receive them from free space. The antenna is responsible for the conversion between free space waves and conducted electromagnetic waves. It forms the interface, so to speak, between the transmitter or receiver and the free-space transmission medium. From an electrotechnical point of view, an antenna is an oscillating circuit with a capacitive (capacitor) and inductive (coil) component that has a specific resonant frequency. In the resonant circuit, the energy travels back and forth between the coil and the capacitor, alternately generating an electric and magnetic field. To realize an antenna, the resonant circuit is supplied with conducted electrical energy on one side. On the other side, the oscillating circuit is open and radiates electromagnetic energy into space or absorbs it from space. With this principle of operation, a simple dipole antenna can be realized with only two wires. 

Classification of antenna types according to radiation characteristics 

Depending on antenna parameters such as polarization, antenna impedance, efficiency, antenna gain, directivity or bandwidth, there are countless different types of antennas. An important criterion for the classification of antenna types is the radiation pattern. Based on an idealized omnidirectional radiator, also called isotropic radiator or point source radiator, which radiates uniformly in all spatial directions, a distinction is made between omnidirectional radiators and directional radiators. The omnidirectional radiator belongs to the omnidirectional radiators and transmits or receives electromagnetic waves in horizontal direction circularly. A typical omnidirectional radiator is the rod antenna. It has a length of lambda/4 (one quarter of the wavelength) and radiates or receives horizontally uniformly at 360 degrees at a 90-degree angle to the antenna axis. 

Directional antennas achieve antenna gain relative to the ideal isotropic radiator in a given spatial direction. Directional antennas include dipole antennas, parabolic antennas, Yagi antennas, or sectional antennas. The directivity can vary greatly depending on the antenna type. While sectional antennas are optimized for a radiation radius of 120 degrees, for example, a directional antenna or parabolic antenna achieves a much higher directivity at a smaller angle and must be precisely aligned with a remote station. 

Use of the different antenna types in mobile communications

Depending on the area of application, mobile communications antennas differ significantly in their design and antenna characteristics. Omnidirectional antennas are usually used in end devices such as smartphones. This is because the devices should be reliably supplied with radio signals from all directions, regardless of their orientation. The base stations of a mobile communications network, on the other hand, are equipped with directional sectional antennas. As a rule, three antennas with a 120-degree radiation direction are arranged sectionally on the radio mast, which together supply the radio cell with 360 degrees. The horizontal radiation direction is slightly tilted downward to achieve better separation from neighboring radio cells. 

If point-to-point connections of the base stations with the core network of the mobile communications provider are required, directional antennas can be used if wired coverage is not possible or is too costly. Distances of many kilometers can be bridged via these directional radio links.