Antenna concept for sectorized beamforming using predefined antenna patterns in small cells

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Future cellular radio systems provide more than before the establishment of small cells to supply many users with high data-rate services. In addition to sports stadiums, airport and rail terminals, shopping areas in inner cities or busy roads may require the use of small cells. Designs regarding cell size, frequencies to be used and access concepts can vary widely. Some embodiments provide user tracking enabled by steerable antennas. The cell radii of these small cells in such a scenario are often given as a few tens of meters. Installation sites for base station antennas as lampposts, bridges, ceilings in shopping centers or stadiums are therefore preferred. Due to the low height of the base station, therefore, even with a relatively small cell, there is a large angular range within which the antenna must be able to steer its radiation lobe. This also results in very different path lengths of the LOS (Line of Sight) connection between the base station antenna and the user's terminal. The amplifier of a TR module of the base station must therefore already cover a large dynamic range, which can lead to low efficiency. Scan Loss, Pattern Loss and Grating Lobes further affect the situation.In the present project proposal, an antenna concept is proposed, in which each antenna element has a plurality of selectable preferred patters, which can be controlled in parallel via decoupled antenna ports. Thus, when steering the antenna lobe per sector a suitable pattern can be selected. The decoupled sectorial TR modules thus only have to have a lower power dynamic range.The synthesis of the multi-port antenna elements is based on the theory of characteristic modes. By means of feed networks, suitable sets of orthogonal modes are excited on the same antenna element.After exploring the basic connections, a beamforming array for a hypothetic small cell in a 5G scenario is constructed as a demonstration example. The antenna properties, in particular with regard to the sectoral beamforming, are investigated by measurements.