Design guidelines for pattern reconfigurable antennas by exploiting the characteristic modes analysis

A novel pattern reconfigurable antenna operating at 2.45 GHz is designed for portable devices by exploiting the characteristic modes analysis (CMA). In particular, a null-steering antenna is proposed by exploiting the current modes distribution (J_n) over a ground plane of the dimensions of a mobile terminal. To achieve this goal, two current modes (J₄ and J_s) are asymmetrically excited by introducing a phase difference (Δθ) between the two capacitive coupler exciters (CCEs) hosted above the conductive plane. More in detail, the position of the CCEs allows exciting only Mode # 4 and Mode # 8, related to the current modes J₄ and J_s, respectively. The phase difference (Δθ) allows controlling the level of the excitation of these modes and obtaining the null-steering antenna in the y-z plane. As a proof of concept, a discrete phase shifter that employs several pin diodes has been designed in microstrip technology in order to obtain a subset of the phase differences. The radiation patterns prove that the proposed design guidelines are reliable and applicable to other kinds of structures.