Leakage from slotted waveguides is a well-known phenomenon and has been thoroughly investigated during the past decades. The interest in leaky-wave antennas mainly stems from the possibility of scanning the beam with frequency [1]. The analysis of slotted waveguides has been first performed by means of a transverse network representation of the open structure since the milestone paper by Goldstone and Oliner [2]. As a matter of fact, the method is simple but accurate, and can be easily extended to deal with structures more complicated than the standard slitted waveguide addressed in [2], such as groove guides and stub-loaded waveguides [3]-[5]. Unfortunately it is not always possible to find a transverse equivalent network, in which case it is necessary rely on more general, but time-consuming, numerical methods.