Orthonormal Beam-Steering for Single-RF ESPAR

An orthonormal beam-steering approach for singleradio-frequency (single-RF) electronically steerable parasitic array radiator (ESPAR) antenna is described. This approach is based on the rotated formulation of N-port Characteristic Modes (CMs), which provides a set of orthonormal, symmetrical and directive steering beams. The method is applicable to ESPAR with arbitrary antenna type or array configuration. Using the symmetry of steering patterns, the load reactance values of ESPAR are symmetrical so that a fixed impedance matching network can be used to simplify the ESPAR design. To verify the proposed approach, two ESPAR configurations, including a linear planar inverted-F antenna (PIFA) array and a circular monopole array, are prototyped with tunable parasitic loads of varactors. Simulation and experimental results verify the effectiveness of the proposed approach that both ESPAR antennas can steer directive and orthonormal patterns towards various directions by tuning varactors while maintaining good impedance matching. This approach is promising for 6G wireless systems.