Computer-Aided Design of a Switchable True Time Delay (TTD) Line With Shunt Open-Stubs

This paper presents a new technique to design switchable true time delay (TTD) lines using periodic shunt open-stubs, shorter than a quarter wavelength at the highest frequency of interest. Structural parameters are obtained by minimizing the group delay variation and maximizing the return loss over the operating band. Advantages of the proposed design are low insertion loss, higher 1 dB compression point, and less number of switches compared to the conventional designs. To verify the proposed technique, 2-states and 8-states TTD lines are fabricated for L- and S-band applications. For the 8-states delay networks, measured insertion losses are smaller than 1.9 dB at 3 GHz. Return losses are more than 10 dB over 1-4 GHz band. Measured maximum time delay is 84 ps for the 8-states delay lines with a step size of 10 ps. All the TTDs operate as linear device at least up to 23 dBm.