Compact Dual-Band Negative Group Delay Circuit

A simple, compact dual band negative group delay (NGD) circuit with independent tuning is shown on this paper. Adding a stubbed open T line to a 2.45GHz coupled line bandpass filter with negative group delay adds a second NGD band at 3.68GHz. The second band can be independently tuned with marginal effect on the first band. A proof-of-concept circuit with $25.4 \mathrm{~mm} \times 30.4 \mathrm{~mm}\left(0.30 \lambda_{g} \times 0.37 \lambda_{g}\right)$ is constructed on Rogers RT Duroid 5880 substrate. Simulated results show two NGD bandwidths at 2.46GHz and 3.7GHz with the first bandwidth on the same region before and after insertion of the T line. Measured results are in agreement with the simulation.