Stopband and Coupling-Coefficient Estimation for Asymmetries in Helical Delay-Lines

The $\pi$-point stopband in helical delay-lines due to asymmetries is analyzed. For this, we model the structure as a conductor-backed coplanar waveguide. The stopband is evaluated from the effective transmission-line parameters and the results are compared to full-wave simulation. Although the approach is quite general, we only consider non-ideal support-rod positions in this contribution. Finally, the stopband is modeled by applying the coupled-mode theory, including a simple coupling-coefficient estimation.