An Investigation of Printed Franklin Antennas at X-Band Using Artificial (Metamaterial) Phase-Shifting Lines

Non-radiating artificial phase-shifting lines are constructed using conventional positive-refractive-index (PRI) transmission lines (TL) and the recently developed negative-refractive-index (NRI) transmission lines. The two types of fully printed artificial lines are used to implement microstrip Franklin antennas. The aim is to provide co-phase excitation to an array of half-wavelength dipoles, which generate a broadside beam at the design frequency. The proposed antenna structures not only retain the benefits of previously published designs but also feature a smaller footprint in the transverse direction. Between the two proposed antenna configurations, the PRI-TL based design allows broadside radiation with minimal beam squinting, while the NRI-TL based design provides a frequency steerable beam. A 14-element antenna array for each configuration is characterized using an intuitive TL model, and the study is experimentally verified at 12 GHz. The measured radiation patterns, directivity, gain, and beam-scanning capability are presented.