Operational Insight of Microstrip Resonators Using Stepped Impedance Transmission Line and Coupled Lines

Abstract

An operational insight of the Microstrip resonator using the stepped impedance transmission line and the recently introduced stepped impedance coupled lines is outlined in this paper. This qualitative description is based upon phasor diagrams of waves propagating along a lossless stepped impedance open-ended line. In essence, it visualizes how the first parallel resonance frequency of the stepped impedance resonator can be shifted up to a higher frequency, or down to a lower frequency, as compared to that of its uniform impedance counterpart. In summary, It is found that the stepped impedance resonator relies upon the use of partial reflections at the stepped impedance junctions between the transmission line sections to perturb the phase shift of the wave propagating one-round along the line, thereby effectively modifying the resonance frequency. Such insightful understanding also brings to light the underlying operation of transmission line perturbation structures in general, and these can be useful for performance enhancement of other microwave circuit building blocks.