Broadband Determination of the Propagation Constant of the Slot Mode of a Rectangular Waveguide

A broadband technique to extract the attenuation and phase constants of the slot mode in a rectangular waveguide from either simulation or measurement results is proposed in this letter. The method is based on processing the values of the reflection coefficient of several slotted waveguides with different lengths and the same termination and feeding. The accuracy of the method can be improved by increasing the number of simulated or measured waveguides. The proposed technique is specially conceived to separate the contribution of the slot mode from other modes. An implementable structure and a measurement method to apply the extraction technique are proposed and used. Measured and simulation results of the proposed technique obtained from waveguides filled with two different materials are shown up to 10 GHz and validated using an approximate model. The proposed method can be regarded as a powerful technique to compute the propagation constants of leaky modes in leaky-wave antennas.