A theoretical and experimental study of the use of thin perfectly conducting fences to reduce the mutual coupling of two parallel-plane waveguides radiating through a ground plane is described. The two cases which are studied are

-plane coupling of parallel planes with transverse electromagnetic mode propagation and

-plane coupling of parallel planes with the fundamental transverse electric mode propagation. The analysis presented accounts for a number of higher order modes in the waveguide apertures and uses a Fourier series approximation to the fence currents. Close agreement with experimental results is demonstrated.