Investigation of the Resonance Phenomenon in a Microstrip to Grounded Coplanar Waveguide Structure

ABSTRACT In this paper, we investigate the resonance phenomenon in a microstrip (MS) to grounded coplanar waveguide (GCPW) to MS structure. We demonstrate that the resonance arises from the relative phase difference between two excited modes in the GCPW. Through modal analysis supported by field plots, we calculate the relative phase difference of the two modes at the start and end of the GCPW section. We show that the reflection from the GCPW‐MS discontinuity depends on the phase difference of the modes. If this phase difference is zero, the reflection is minimum due to destructive interference of the reflected waves. Therefore, the resonance in a MS‐GCWP‐MS structure can be suppressed by modifying this phase difference. An analytical analysis based on multiconductor transmission lines is employed to verify the full‐wave analysis. Two approaches are proposed to modify the relative phase difference. The first approach is to use an overlying dielectric to slow down the dominant mode. The second approach slows down the dominant mode by increasing the equivalent capacitance of this mode with periodic stubs and speeds up the common mode by removing a portion of the substrate below the coplanar grounds.