Perturbation analysis and modeling of curved microstrip bends

The curved microstrip bend consisting of a microstrip ring segment between two microstrip lines is analyzed for its transmission properties. The microstrip lines are modeled by equivalent ideal magnetic wall waveguides for which the electromagnetic field solutions are known. The field solutions in the microstrip ring segment are derived by using a perturbation analysis of a modified (magnetic wall) curved waveguide model. Other techniques have been formulated to evaluate the fields inside curved metallic waveguides. These include the use of an equivalent nonuniformly loaded straight waveguide and rectangular and annular model analysis. The perturbation solution for the fields in the equivalent curved waveguide model presented is readily adaptable to the mode-matching procedure, and is used to calculate the properties of the curved microstrip bend discontinuities. The frequency-dependent reflection and transmission coefficients of curved microstrip bends are determined and compared with those of the right-angle and chamfered right-angle microstrip bends.>