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.