Research on the Radiation Characteristics of Patched Leaky Coaxial Cable by FDTD Method and Mode Expansion Method

Patched leaky coaxial cable (PLCX) is proposed as an alternative to the conventional leaky cable for wireless links in a complex environment. It is expected to have the capability of adjusting the coupling between the cable and the environment and give smoother electric field coverage. In this paper, the radiation characteristics of the PLCX with general inclined patches are studied by a hybrid method that involves the finite-difference time-domain (FDTD) method for the near-field computation and the mode expansion method for the transformation of near field to far field. In the method, the space around the patched leaky cable is divided into two regions by an artificial closed cylindrical surface that is incorporated with the FDTD lattice surface when implementing the FDTD iteration. The field distribution on the artificial surface is obtained after the implementation of the FDTD method. Meanwhile, the field outside the artificial boundary is expanded in terms of the Floquet modes with coefficients to be determined. By matching the field expressed by modes and the field obtained from the FDTD method at the artificial boundary, a matrix equation with unknown coefficients is obtained. Solving this matrix equation, the expansion coefficients are known, and the field outside the artificial boundary is ready to be obtained.