Smart antennas for high spectral efficiency
We are surrounded by an invisible sea of electromagnetic waves. Continuously, and in all directions of space, they transport energy from a number of sources: cell phones, televisions, radio, satellites... This incessant electromagnetic cocktail seems safe for our health, but it limits, in a significant way, our ability to send and receive information.

We are surrounded by an invisible sea of electromagnetic waves. Continuously, and in all directions of space, they transport energy from a number of sources: cell phones, televisions, radio, satellites... This incessant electromagnetic cocktail seems safe for our health, but it limits, in a significant way, our ability to send and receive information. The more we communicate, the more interference from these radio waves multiplies, and to overcome the din of electromagnetic background noise, we must amplify the radio signals that are emitted. In this way, we reinforce the interference.

The key to the problem lies in the use of a class of antennas that reduce interference. While a conventional antenna broadcasts electromagnetic signals in all directions (omnidirectionnal antennas), these antennas detect precisely the position of the users and deliver signals only in their direction. In addition, they can optimize the reception of a communication from a receiver, while minimizing interference with possible signals from other systems These antennas are known generically as adaptive (or smart) antennas. Among them, the most powerful are adaptive antenna arrays, which combine several multiantenna panels and powerful software. These adaptive antenna arrays can be integrated into an existing telecommunication network, or developed for new networks, and are expected to increase the quality of wireless telecommunications while reducing the cost of operation. Capable of receiving and transmitting large quantities of data.

To understand how a smart antenna works, let's first go back to how conventional antennas work. An antenna transforms an electrical current and voltage into an electromagnetic wave. However, it can also receive a wave propagating in space and transform it into electricity. The simplest of antennas is the dipole. Made of two metal wires, it diffuses energy uniformly in all directions in space. The farther a wave travels, the more its amplitude decreases, like the small waves that form on the surface of a lake around the impact of a stone. In addition, electromagnetic waves can be absorbed or reflected in their path by obstacles such as air, trees or buildings.

Focus on the receiver

In order to have the largest possible diffusion, television channels or radio stations try to broadcast far away and in all directions (Omnidirectionnal Diffusion). On the other hand, a telephone call only concerns two people. In a cell phone network, each user communicates with the nearest base station, which concentrates all the communications transmitted by users located in the vicinity, in an area called a cell. The area covered by a communication network is divided into cells, and when a user changes cells, the signal associated with his communication is automatically switched from one base station to another, more appropriate. In this situation, the ideal would be to focus the energy corresponding to a transmission only towards its recipient, like a light reflector re-emitting light rays in a directional way. In this way, all the energy associated with a communication would be concentrated in one direction, rather than being dissipated throughout the space. The signal would be more intense over a greater distance. In addition, the signals from different communications would be well separated, reducing the risk of interference.

Definition of Antenna Array

An antenna array is the regular association of similar antennas to create a radiation with a specific pattern. The radiated power is systematically higher due to the increase in the number of radiating elements. The radiation results from the addition in phase of the fields coming from each element composing this association of radiating elements. The possible arrangements are thus multiple and generate a great flexibility in the design of arrays.
Antenna arrays are used for multiple purposes and use several types of elements: wire , horn , printed antennas and others.

The antenna array occupies a larger space than the single antenna (Figure 1), therefore its radiation pattern is narrower as its directivity increases with its surface (Figure 2).

Figure1 : Triangular array patch antenna with 1 element, 2 elements et 4 elements [1],[2]
Figure 2: Radiation pattern for single element antenna vs array antenna

Phased Array Antennas

An antenna array is a set of elementary antennas designed in a way to satisfy a number of specific radiation requirements (gain, directivity, radiation pattern, Side Lobe Level (SLL),
Half Power Beam Width (HPBW), and others). We can respond to some specifications by controlling the constructive recombination and destructive depending on the spatial
relocation of radiating sources. There are several geometric configurations of antenna arrays which can be grouped as follows:

  • Linear network
  • Planar network
  • Circular network
  • Volume network

The formation of the beam depends on several factors such as: the geometry and the position of antenna elements, the distance between them, their excitation phases, the radiation pattern of a single element

The formation of the beam depends on several factors such as: the geometry and the position of antenna elements, the distance between them, their excitation phases, the radiation pattern of a single element.

the term smart antenna means the intelligent orientation and adaptation of the antenna radiation to a specific purpose and this can be achieved with the help of some electronic systems controlling the antenna excitation.

Beamforming : A smart use of the radiation pattern

Beamforming is a technique by which an array of antennas can be directed to transmit radio signals in a specific direction. Rather than simply broadcasting energy in all directions, antenna arrays that use beamforming determine the direction of interest and send/receive a stronger signal beam in that specific direction (figure 3).

Figure 3 : 4G Base Station (eNode B) with Beamforming

This technique is used extensively in radar and sonar, in the biomedical field, and particularly in communications (telecom, Wi-Fi), especially 5G - where very high data rates are required and the only way to support them would be to maximize the efficiency of transmission and reception using beamforming.

In this technique, each antenna element is fed separately with the signal to be transmitted. The phase and amplitude of each signal are then added constructively and destructively so as to concentrate the energy into a narrow beam or lobe.

Figure 4 illustrates a 4-element antenna array fed by an intelligent system allowing the antennas to be fed with phase-shifted signals of specific configurations in order to have a beamforming

Figure 4 : Adaptive antenna array beamforming [3] 

Application Fields of Smart Antenna Technology

1-Satellite communications

In the satellite communication systems, the required signal quality is becoming more important and the traffic quantity is constantly increasing. We are thus witnessing the establishment of system specifications that must combine
performance and flexibility. For the antenna, this translates into constraints on the number of diagrams to be formed for the cover and the number of sources necessary for their control. The use of smart antennas is a solution to this problem. to improve the performance and capacity of satellite systems

Adaptive antenna processing has several potential advantages in satellite systems:
1- It allows the beam to be pointed towards the user, giving the user the maximum possible gain. The interest is either to reduce the size of the user terminal, or to reduce the size of the satellite antenna, or to keep the antenna's size.
unchanged antennas while improving the link budget, thus potentially improving the throughput of the communications concerned.
2- It improves the isolation between users using the same resource, allowing the same frequency band to be reused on two closer beams.
3- Finally, it allows holes in the antenna pattern to be placed in the direction of possible external jammers in order to introduce anti-jamming into the system and thus preserve communications.

2-Radars

Radar antennas are used in the military and civil fields. They can, for example, equip a mobile vehicle in charge of detecting the position of a vehicle. other vehicles, perform missile guidance, carry out surveillance missions or even terrain mapping. The integration of a new technology in radars consists in the realization of an adaptive multibeam antenna, with beam formation by calculation, whose beams are notably free of parasitic network lobes. This multibeam antenna also has a spatial selectivity to the transmission. This system applies in particular to to the fight against radar jamming.

3- Mobile communication

Smart antenna technology allows the capacity of cell phone networks to be increased without installing new antennas. However, the sectorial or omni-directional antenna supports calls made by cell phone users in the area it covers. These coverage areas are called cells and their size is fixed. When many calls are trying to access the mobile network simultaneously, the capacity of a cell may be insufficient, making the network saturated and it is impossible to make calls. The technology of smart antennas allows to modify the geometry of the cells according to the traffic. A part of it can thus be temporarily shifted to an adjacent cell that is little used. The system allows the antennas to talk to each other and distribute resources to the areas that need them the most.
The adaptive antennas that can equip the new generations of base stations are used to direct beams to communicating mobiles and thus to work at reduced power. Beam steering is achieved by controlling the amplitude and phase of the carrier sent to each elementary antenna. Inter-cell interference and disturbances will be reduced accordingly, allowing frequency reuse in closer cells than with antennas. classics.
Beam-switched antennas can also equip base stations of telecommunication systems to widen the coverage area and reduce electromagnetic pollution.

4- WiMax

Smart antennas are also a technological means of improving the performance of WiMax (Worldwide Interoperability for Microwave Access) broadband wireless networks. Indeed, mobile WiMax supports a wide range of these antennas to result in a much more efficient system.
This technology includes:
1- Beamforming: The system uses multiple antennas to transmit signals and improve its coverage and capacity while reducing the probability of outage.
2- Space-Time Code (STC): Transmission diversity such as that of the Alamouti Code is supported to provide spatial diversity and reduce fading margin.
3- Spatial Multiplexing (SM): Several streams are transmitted through different antennas. If the receiver has multiple antennas, it will be able to separate the streams to achieve a much higher throughput than that achieved with a single antenna.

5-Wifi

Recent technological advances have made WiFi much smarter and more attractive with a view to building very affordable wireless broadband access networks. New smart antenna, RF management and interference protection technologies have also significantly improved the overall throughput and reliability of extended WiFi networks by avoiding packet errors.
Unlike omnidirectional antennas that transmit signals in all directions at once, the adaptive antenna array directs all transmitted energy to the receiving device, optimizing range while minimizing noise for surrounding WiFi devices that are not in the signal path.
Also unlike fixed directional antennas, antenna control algorithms form beams by destination and packet by combining one or more antenna elements. With thousands of beams covering all directions and all signal polarities, adaptive antenna arrays are flexible, adaptive and universal.
This automatic adaptation alleviates the burden on wireless installers in terms of accurate positioning of outdoor WiFi radios and antenna tuning.

References

[1] OUADIAA BARROU, Abdelkebir EL AMRI, A.REHA,  Performance Comparison Between FIT and MoM Based Solvers For Microstrip Patch Array Antennas With Conventional Geometries, International Journal of Computer Engineering and Information Technology, Vol. 10, N° 12, December 2018.

[2] OUADIAA BARROU, Abdelkebir El Amri, A.REHA and Mohamed Tarbouch, "Microstip patch array antennas based on conventional geometries", 3rd International Conference on Electrical and Information Technologies November 15-18 , 2017, Morocco  ICEIT 2017. IEEE Conference  DOI 10.1109/EITech.2017.8255305

[3] Minoli, D. (2015), Advances in satellite communications, London, Wiley

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