Nonideal radiation pattern of simple leaky-wave antennas explained in terms of free resonant modes

A slotted rectangular waveguide and a channel guide antenna are considered. It is theoretically and experimentally shown that two leaky-waves must be taken into account for the far field evaluation. It is also shown that the main lobe of the radiation pattern of the channel guide antenna is due to a complex mode other than that found as a perturbative solution