Arbitrary length zero-phase substrate integrated coaxial lines using NRI-TL metamaterials

Arbitrary-length zero-degree phase-shifting lines are presented at X-band that are based on negative-refractive-index transmission-line (NRI-TL) metamaterials implemented in substrate integrated coaxial line (SICL) technology. Initially, a host substrate integrated coaxial line was loaded with a series interdigital capacitor and shunt printed inductors to form a single NRI-TL metamaterial unit cell. Subsequently, multi-stage NRI-TL metamaterial lines were realized by cascading multiple NRI-TL metamaterial unit cells. The performance of the metamaterial lines is analyzed based on their reflection loss, insertion loss, radiation loss and insertion phase for different lengths of line ranging from λ/5 to λ at 10 GHz. It is shown that the radiation loss remains below 0.003% of the total losses for all presented lengths of metamaterial lines, while exhibiting good reflection and transmission characteristics. These results indicate that the proposed zero-phase NRI-TL metamaterial lines in SICL technology are well suited for very low-loss guided-wave applications.