Efficient Integral Equation Analysis of 3-D Rectangular Waveguide Microwave Circuits by Using Green’s Functions Accelerated With the Ewald Method

In this contribution, an electric field integral equation (EFIE) formulation is proposed, for the analysis of microwave circuits based on rectangular waveguides with an unlimited number of arbitrarily 3-D-shaped conducting elements. For this purpose, the Lorenz gauge rectangular waveguide Green’s functions are used. Moreover, the Ewald method has been employed to significantly speed up the evaluation of these rectangular waveguide Green’s functions. Strategies are also proposed to switch between different ways of calculating the Green’s functions depending on the source-observation distance along the propagation direction. In addition, the method of moments (MoM) has been applied to solve the EFIE. Following the application of this technique, the impedance matrix resulting from the MoM has been divided into dynamic and static parts, thus reducing the computational time required to obtain the frequency response of practical 3-D microwave circuits by up to a factor of 3 compared with the traditional formulation. On the other hand, a generic expression is derived to evaluate the multimode scattering parameters of rectangular waveguide circuits, independently on the mode used to excite the structure. The evaluation of the electromagnetic fields inside the rectangular waveguides has also been carried out. The proposed technique has been validated by comparison with results provided by commercial full-wave software, such as ANSYS HFSS and CST Studio Suite, showing good agreement and good numerical efficiency.