An approximate method to calculate the reflection coefficient of a rectangular open-ended waveguide

The open-ended rectangular waveguide is a simple radiating structure, and a lot of effort is being spent on calculating the reflection coefficient or admittance of the structure accurately. In order to improve the accuracy of the result, more rectangular waveguide higher order modes are considered. Meanwhile, amount of computation is increased. A major thrust of the paper is to discuss approaches and strategies for calculating the reflection coefficient of the open-ended rectangular waveguide with a flange radiating directly into the half-space efficiently. The method involving Fourier analysis and waveguide mode expansion method is showed. According to the previous works and results, only TE30 mode which has a greater influence on the accuracy of numerical results than other higher modes is considered to be calculated. The VSWR and phase of the X-band rectangular terminated with a finite size flange were simulated by HFSS, and the measurements also were obtained. The flange of waveguide is discussed with finite size. On the basis of simulation results, the size of flange was determined as 40 cm square, and the aperture is 22.86mm × 10.16 mm. The numerical results are in good agreement with simulation and measured results. The VSWR maximum deviation is less than 0.05 and the phase maximum deviation is less than 10 degrees between numerical and measured results during the effective calibration frequency range.