# Adaptive Antenna Array Control Algorithm in Radiocommunication Systems
## 4 Model and Experimental Tests of an Adaptive Microstrip Antenna Array  
The adaptive algorithm is implemented in the adaptive antenna. The designed antenna is an adaptive antenna. Its task is to radiate such characteristics as to provide all serviced subscribers from a given sector with appropriate connection quality. The antenna sector is 120\({}^{\circ}\), so the characteristics should be deflected by almost 60\({}^{\circ}\) to the right and left from the direction marking the center of the sector to ensure coverage of the entire sector. The antenna's radiation pattern will have to be variable so as to cover all subscribers served at a given time. The adaptive antenna must have the following features:  
* Small changes in antenna parameters across the entire frequency band;
* Wide (sufficient to cover the sector) beam scanning range;
* Ability to change the shape and direction of the main beam;
* Asymmetrical characteristics in the facade, tilted towards the ground by 6-10\({}^{0}\)
* Low level of side lobes;
* Good ratio of forward radiation to backward radiation of a single radiating element;
* WFS level < 2;
* Directional gain of 10-15 dB;
* Antenna consisting of eight identical elements;
* The statistical parameters of the useful signal are known;
* The direction of arrival of the useful signal changes over time;
* This direction is determined based on the phase difference of signals received in neighboring component antennas (in the model, the phase difference is determined based on the assumed signal arrival angle);
* Interfering signals occur in the given directions, and their location does not change in time;
* The powers of useful and disturbing signals are constant and unchanging in time;
* It is possible to carry out simulation tests for various values of the assumed parameters (number of useful and interfering signals, their powers and locations, and the movement they perform, number of antenna components, etc.) The algorithm of the adaptation process is usually based on one of three classic methods. Two of them use the concepts of controlling weighing systems with feedback [23]. The first one requires information about the actual and potential location of the sources of the desired signals. It is often called the power-inversion algorithm or Applebaum-Howell's algorithm. The second method of determining weights, using feedback control, is called Widrow's algorithm. In order to maximize the signal-to-noise ratio for signals received from a single desired signal source, the characteristics of the desired signal are required here. The third method, which does not use feedback, SMI sample-matrix-inversion, is based on an algorithm that is a completely computational process, using signals received from N ports of the adaptive antenna and the angular position of the desired signal source. Thanks to this information, interfering signals are suppressed at the output. The SMI algorithm does not use feedback to correct implementation inaccuracies (Figure 6). The system is composed of several components, the most important of which are:  
* Antenna array;
* Microwave coupler systems;
* Frequency conversion block (there are solutions without frequency conversion);
* IQ metabolism systems;
* A/D converters;
* A signal processor based on an implemented algorithm for determining complex weights;
* Weighing systems. The digital signal processing path consists of:  
* A/D converters;
* One or two signal processors;
* Digital weighing systems. The selection of parameters of each component affects the accuracy and speed of the adaptation process, which results in obtaining the desired directivity characteristics or determining the directions of incoming signals. The adaptive algorithm uses information developed solely on the basis of:  
* Output signal \(s_{o}\) (weigh-dither algorithm);
* \(s_{n}\) input signals. (inversion-matrix algorithm);
* Signals \(s_{o}\) and \(s_{n}\) algorithm (Applebaum-Howell's and Widrow).