Calculating the mutual coupling between apertures on a convex circular cylinder using a hybrid UTD-MoM method

The problem of calculating the mutual coupling between apertures on a perfectly conducting circular cylinder is considered. The mutual coupling is calculated by a combination of the uniform theory of diffraction (UTD) and the method of moments (MoM). This hybrid method makes it possible to include higher order aperture modes in order to improve the accuracy. It is found that the UTD-MoM solution gives accurate results, even for small cylinders. The results are verified against results found in the literature, as well as against measurements performed at Ericsson Microwave System in Molndal, Sweden. For this purpose, a cylindrical test antenna with 54 apertures was built. Using a single-mode approximation, good agreement, down to about -60 dB, with comparisons to measured data has been obtained. If additional modes are added the results improve significantly, both in amplitude and phase. In several cases, the agreement is good down to coupling levels of about -80 dB. This requires that about six modes are included. However, the most important mode, besides the fundamental TE₁₀ mode is the TM₁₁ mode