Unidirectional reciprocal DC-block impedance transformer with flatness and broadband negative group delay characteristics

A novel unidirectional reciprocal DC-block impedance transformer with flatness negative group delay (NGD) characteristics and enhanced NGD bandwidth is proposed, which is composed of four-section transmission lines (TLs), four-section coupled lines, and three resistors. The combination of series resistors and short-circuited coupled-line sections improve the NGD bandwidth and strengthen the flatness of NGD response. Moreover, the used coupled lines achieve an inherent DC block. For demonstrations, three typical ideal examples operated at the center frequency of 3.5 GHz are designed and simulated, respectively. The simulated results show excellent agreement with theoretically predicated performances including good matching, enhanced NGD bandwidth, and high NGD flatness.