Electric-Field Null Bending of a Single Dual-Port Patch Antenna for Colinear Polarization Decoupling Using Characteristic Modes Analysis

A novel design concept for bending the electric-field nulls of a single dual-port microstrip patch antenna (MPA) for colinear polarization decoupling is proposed in this communication. Initially, the electric-field distributions of the traditional MPA are theoretically studied by using characteristic mode analysis (CMA). The results demonstrate that the of electric-field nulls could be bent by combining its two modes. Hence, when the antenna is excited at the left port, electric-field nulls could be formed around the right port. In contrast, electric-field nulls are formed on the left port for the MPA under excitation of the right port. Next, a set of shorting pins is loaded below the radiating patch. Hence, the MPA reallocates the resonant frequencies of these dual modes closely to each other and combines them for low mutual coupling. After that, the slot is cut on the radiator, aiming to improve the impedance matching over the operating band. With these arrangements, the mutual coupling of the MPA between dual ports is successfully decreased with good impedance matching. In final, the proposed MPA is fabricated and measured. Good agreement between the simulated and measured results is obtained, and it proves that the $\vert S_{11}\vert < -10$ dB of the antenna is operated in a range from 5.3 to 5.54 GHz. Besides, the antenna maintains the low-profile, single-layer, and single-element properties. Most importantly, it has generated a broadside radiation pattern with the same polarization, and its isolation is satisfactorily enhanced to above 17 dB, which is much higher than the 3.5 dB of the traditional counterpart. Hence, it can be used for in-band full-duplex (IBFD) systems.