Artificial lines with exotic dispersion for phase shifters and delay lines

We discuss various possibilities to design phase shifters with reduced frequency dispersion using combined sections of forward-wave and backward-wave transmission lines. It is shown that inclusion of backward-wave sections into a single transmission line always increases the total dispersion. On the other hand, we show that dispersion can be reduced by means of lines with positive anomalous dispersion and provide an example of such line. Furthermore, we report the theory and design of a novel phase shifter, based on parallel combined backward-forward transmission lines. The phase shifts, produced by this device, are characterized with negligible frequency dependence in a wide frequency range. We show that for an ideal performance, phase deviation can be less than 1° within a 20% bandwidth while excellent impedance matching is retained. We support these theoretical estimates by microwave circuit simulations and direct measurements, showing that the novel phase shifter can be easily implemented with simple electronic components.