## 1 Introduction  
The world is gradually undergoing the age of communications, facing an enormous density of traffic and connections, where everyone is online, people and objects, interacting with each other, through a multitude of applications [1]. The modern generation of mobile communications (5G) is launched, which brings new challenges and opportunities, and will allow the creation and integration of new networks such as the internet of things (IoT) and vehicular networks, in an increasing global coverage. These systems impose a set of new requirements such as high speed data transfer, low latency, high network capacity and high connections density [2], which involve the operation in a frequency range little used so far, in the zone of millimetre waves. Radio detection and ranging (RADAR) technology, that was mainly used for military purposes, recently has suffered increasing attention, and its application is nowadays widespread in sports, biomedical, military or in transportation systems. Radars are used for surveillance, navigation, localization, traffic control or for weapons guidance. Currently, with the evolution of vehicular networks, smart cities and other intelligent systems, more advanced radar technologies are being developed. In the near future, the extension of the radar concept is expected for two purposes, reflectometry and communications. The scenario of Figure 1 is foreseeable, a panoply of interconnected systems sharing information, and experiencing a huge communications density, with high risk of interferences. Radar technology is required to filter the environment, focusing more accurately on the target or targets, as well as to mitigate interference signals from the surrounding environment. Multibeam capabilities, beamforming, high gain and tremendous versatility and reconfigurability are important aspects for modern radar systems. Additionally, most of these characteristics allow us to overcome propagation issues raised when these systems operate at higher frequencies. Thus, versatile and dynamic communication systems are needed, with the ability to continuously adjust to the applications in which they are inserted, maximizing the quality of communication. With additional signal processing capability, adaptive antennas use new digital architectures that, in real-time, dynamically adjust the radiation pattern of the array. These systems have perception of the received signal and optimize their radiation diagrams by changing the beam shape and beam direction, suppressing interferences by introducing nulls in the directions of the interference signals, changing the level of side lobes, compensating for hardware impairments and finally, accommodating the mutual coupling effects that can change the amplitude and phase of the transmitted signals. Particularly regarding automotive radars, the authors of [3,4] present a good example of the importance of using digital beamforming in multiantenna systems to reduce the power received in the directions of interference signals, placing nulls in the radiation pattern. There have been technological advances in this field, where low-cost mm-wave radars composed of several antenna elements integrated in single board and with high resolution, have been presented. In [5] is presented an example of a low-cost digital beam steering receiver (Rx) phased array for IoT device connectivity, a cheap application to get over the communication problems. In [6], a frequency modulated continuous wave (FMCW) radar is described. This system generates multiple digital beams with high gain, low side lobe level, narrow beam width and high angular resolution control. The principles of the digital beamforming applied to synthetic aperture radar (SAR) systems are shown in [7], as well as the improvement in the resolution achieved regarding conventional radars. In [8,9], a wide variety of future applications are shown, as well as the progress that technology is facing in reducing the cost of phased array antennas.