Compact composite right/left-handed transmission line unit cell for the design of true-time-delay lines

This study presents a novel composite right/left-handed transmission line (CRLH TL) unit cell with high time-delay (TD) efficiency for the design of true-time-delay lines (TTDLs). Shorter inter-digital fingers are used in a symmetrical CRLH TL unit cell to reduce the size by 58% and form a compact CRLH TL unit cell. This reduces the left-handed (LH) capacitance, which is compensated by using open-circuited metallic vias on the fingers. A TTDL constructed by cascading a number of compact CRLH TL unit cells is designed and studied using computer simulation, and then fabricated on a PCB for measurements. For performances comparison, two other TTDLs of the same length implemented using the symmetrical CRLH TL unit cells and right-handed transmission line (RH TL) are also designed, fabricated and measured. Simulation and measurement results show that, for the same length of 30%mm, the TTDL implemented using the compact CRLH TL unit cells has much longer time delay than that of using the symmetrical CRLH TL unit cells and the RH TL.