Compact Negative-Refractive-Index Transmission-Line (NRI-TL) coupler, filter and diplexer

This work demonstrates how certain properties of Negative-Refractive-Index Transmission-Line (NRI-TL) metamaterials can be utilized to miniaturize conventional microwave devices used to feed antennas. Specifically in NRI-TLs small values of the loading elements lead to large phase shifts per-unit-length, thus facilitating miniaturization. Using this principle, a compact NRI-TL branch-line coupler (85% area reduction) is presented. Moreover, a filter is presented with a performance that is similar to a four-stage coupled-line filter that is twice as long. Finally, these building blocks are combined to synthesize a compact NRI-TL diplexer that can separate two closely spaced frequencies (1.95 GHz / 2.03 GHz) with a minimum of 20 dB isolation.