Compact passive and active tunable delay lines using complementary split-ring resonators

A novel compact left-handed delay line using four-cell of complementary split-ring resonators (CSRRs) has been designed, fabricated and characterised. It is found that the cell separation of CSRRs has significant effects on time delay. To obtain maximum time delay, each cell separation must be individually tuned and optimised. The results show that cell separation optimisation can prolong the delay time from 0.6 to 6.08 ns, increased by more than 90%. Furthermore, varactor diodes were embedded in the delay line to provide tunability. It is verified experimentally that the delay time can be tuned from 0.08 to 5.6 ns by varying DC bias from 0 to -20 V. In addition, a new equivalent circuit model has been developed and verified both numerically and experimentally, to take into account of the magnetic coupling between the rings in the adjacent cells, which has been neglected so far in published works. The proposed analysis reveals that such magnetic coupling can be sometimes very strong and has significant effects on circuit performance.