Coplanar waveguide is a key structure in cross-scale transmission structure of System-in-Package (SiP). In this paper, an analytical model for the radiation field distribution of coplanar waveguide structure is established based on the analytical approximation method. In this model, the upper groung plane of the coplanar waveguide is treated as a binary slot antenna array. And, the Babinet’s principle and duality principle are used to make the binary slot array equivalent to the binary traveling-wave array. And, the mirror image principle is used to make the lower ground plane of the coplanar waveguide equivalent to the binary traveling-wave array, with same current amplitudes and opposite phases to the former. According to the analytical model proposed in this paper, the radiative directivity of the coplanar waveguide is analyzed and regulated, and parameter scanning analysis is performed on the length of the coplanar waveguide. Compared with the finite element model, the analytical model not only has less than 5 \(\%\) phase error in the main radiation direction and has lower time complexity, but also can be used to analyze and regulate the radiation characteristics of coplanar waveguides from theoretical level.