Slow-wave inductively-loaded electromagnetic bandgap (EBG) coplanar waveguide (CPW) transmission lines and application to compact power dividers

In this work, a miniaturized power divider based on inductively-loaded coplanar waveguide (CPW) transmission lines is presented. Due to the presence of series inductors, implemented by symmetrically etching rectangular slots in the ground plane, the phase velocity of the proposed inductively-loaded lines is smaller than the phase velocity of unloaded (ordinary) CPWs. This slow-wave effect, related to the increase of the effective inductance of the line, reduces the guided wavelength, and hence the size of any circuit implemented by means of these artificial lines. For the design of these periodically loaded lines, the characteristic (or Bloch) impedance, ZB, and the electrical length of the unit cell at the design frequency, βl, are set to certain values, dictated by the specific application. The slow-wave ratio (swr), defined as the ratio between the phase velocities of the loaded and unloaded lines, determines the level of compactness of the final circuits. The expressions providing the electrical parameters of these artificial lines (ZB and βl) are derived and validated through an illustrative example. Finally the design of a compact power divider operating at 1 GHz, exhibiting 50% size reduction as compared to the conventional counterpart, is reported.