This analysis modifies and improves the moment method analysis
presented in 121 and is based upon the method developed for
microstripline discontinuities [4] and the aperture-coupled microstrip
antenna is]. The entire domain basis functions are used for the electric
current density on the microstrip antenna. Only fundamental mode is
assumed propagating on the slots of the coplanar waveguide away
from the open end. To account for the higher order modes in the
vicinity of the discontinuity. subsectional roof-top basis functions are
used for the magnetic-current density in the slots of the coplanar
waveguide near the open end. The magnetic-current density on the
open-end slot is also expanded by the same roof-top functions.