NEW FORMULAS FOR THE REFLECTION COEFFICIENT OF AN OPEN-ENDED RECTANGULAR WAVEGUIDE RADIATING INTO AIR INCLUDING THE EFFECT OF WALL THICKNESS OR FLANGE

New formulas are presented for the reflection coefficient at the open end of a rectangular waveguide radiating into air including the effect of wall thickness or flange. Existing formulas require significant amount of numerical calculations and do not cover the practical range of waveguide dimensions. Reflection coefficients of open-ended standard waveguides are simulated using commercial electromagnetic software and curve-fitted to derive new formulas. Proposed formulas also include the effect of the broad-to-narrow wall aspect ratio. The accuracy of proposed formulas is compared with existing analytical, numerical and experimental results.