Quad-band negative-refractive-index transmission-line unit cell with reduced group delay

A generalised negative-refractive-index transmission-line (G-NRI-TL) lattice topology is used to design a quad-band phase-shifting cell with half the group delay of previous G-NRI-TL cells and perfect matching at all frequencies. The all-pass lattice topology reduces dispersion at the operating frequencies for lower group delay performance. Design equations are presented that determine the lumped element values necessary to match the structure while achieving a given phase at four arbitrary frequencies. This transmission-line cell is useful for implementing passive quad-band microwave elements with enhanced bandwidth performance.