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This paper presents the mode symmetry analysis and design of CMOS synthetic coupled lines that are meandered for the miniaturization design. The conventional even-odd mode analysis is not appropriate to apply due to the meandering structure, which is asymmetric. The asymmetric coupled-line model is therefore adopted for analyses and the equivalent model parameters are extracted based on ABCD-parameters converted from scattering parameters. The proposed extraction procedure is then applied on a 3-dB directional coupler as a design example. The results quantitatively show that symmetry of the coupled lines is well maintained. Symmetry of other coupled-line structures that degrade coupled-line symmetry, such as loosely coupled lines and different bend direction, are also analyzed based on this model. Finally, an equal-length bend design suitable for the CMOS synthetic coupled lines is proposed and has managed to improve symmetry on various structures.
Microwave Theory and Techniques, IEEE Transactions on (Volume:59 , Issue: 8 )
Date of Publication: Aug. 2011