Beam-Steering in Super-Directive Antenna Arrays Using Loaded Parasitic Elements

Super-directive antenna arrays (SDAAs) suffer from low realized gain caused by high impedance mismatches and low radiation efficiencies. Additionally, since the maximum radiation is directed only towards the end-fire, the practical applications of SDAAs have been historically restricted due to their limited coverage area. When classical phase shifters are employed for beam-steering, there is a significant decrease in the gain attributed to the amplified sensitivity of the realized gain to antenna feed currents. Therefore, innovative beamforming network (BFN) configurations are required to direct the beams while maintaining high realized gain in SDAAs. To address this fundamental challenge, we introduce a novel configuration employing parasitically loaded elements for beam-steering applications within a four-element array, aiming to achieve high realized gain. Firstly, the effect of the parasitic elements’ positions on the array’s beam-steering performance is examined. Subsequently, a reconfigurable BFN is introduced, incorporating adjustable passive circuits within the parasitic elements, which remain in fixed positions. The configurations obtained through multi-parameter optimization are analyzed in full-wave electromagnetic simulation software, and the results are presented comparatively. The common belief that constrains the practical applications of SDAAs – that "maximum radiation is directed towards end-fire" – is challenged as a result. Testament to this, we achieve a 34% increase in gains compared to a uniform uncoupled array for the final loaded configuration, augmented with the ability to steer the beam towards any desired direction.