An asymptotic solution based on high-frequency approximations is proposed to determine the scattered waves from a wide empty isosceles triangular cavity. The modal method based on cylindrical wavefunction expansion with the physical optics technique is used to find analytical expressions for the unknown expansion coefficients and significantly improve the time efficiency of calculations. Some assumptions and simplifications are made to reduce the complexity of the problem while still being accurate for wide triangular cavities. Comparisons are achieved to illustrate the validity and time efficiency of the suggested solution.
