UWB true-time-delay lines inspired by CRLH TL unit cells

Abstract

This article presents the design of ultra-wideband (UWB) true-time-delay lines (TTDLs) operating in microwave frequency.The design is inspired by the use of composite right/left-handed transmission line (CRLH TL) unit cells as the true-time-delay elements to obtain large time delay. A rotated version of the CRLH TL unit cell is used to achieve UWB operation. A periodic microstrip line (PML) employing a sawtooth-shaped periodic pattern is used to further increase the time delay. For comparison, TTDLs using the conventional CRLH TL unit cells, the PML and the right-handed transmission line (RH TL) are also designed, optimized and fabricated. Simulation and measurement results show that, for a same length of 60 mm, our proposed TTDL has an ultrawide operating bandwidth and much larger time delay than those of the PML and RH TL ones. Moreover, it has the advantages of high return loss and low insertion loss. Finally, for easily fitting to practical circuits which normally occupy rather even widths and lengths on the printed circuit boards, the proposed straight UWB TTDL is bent to form different shapes such as circular, rectangular and meander. Results show that the performance of the TTDL is not degraded by bending into these shapes. © 2011 Wiley Periodicals, Inc.