Ralph T. Muehleisen
David C. Swanson
Appl. Res. Lab., Penn State Univ., University Park, PA 16802
Reflection coefficients for higher-order modes impinging on the ends of finite rectangular ducts were predicted and measured. The results show coupling between propagating and evanescent modes. Expressions for the reflection coefficients in terms of modal coefficients and modal impedances have been developed. Radiation patterns were predicted from the knowledge of the coupling coefficients. It was found that higher-order modes radiate most of their energy off towards the sides and less straight ahead than the plane wave mode.