Coupling properties of any two longitudinal slots in the wider walls of a rectangular waveguide are analysed. The theoretical results are in good agreement with the experimental results and with the data previously obtained （for single slot and half-wavelength slots）. Based on the calculated and the experimental results

the electric field distribution at the aperture surface

the admittance

the resonant conductance

and the resonant length of the slots are discussed

taking into account both the effects of external and internal mutual coupling between the slots. The effects of the waveguide wall thickness and narrow-side width are also discussed.