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A simple topology of an NGD active circuit consisting of a FET terminated by a shunt RLC-resonant network and dedicated to the microwave signals was proposed and extensively studied. To our knowledge, in this chapter, the first experimental time-domain demonstration of a circuit able to exhibit simultaneously gain and NGD in microwave domain is proposed. By injecting in the NGD circuit a sufficiently smoothed input short-pulse modulating a sine carrier, one gets an output having an envelop peak in advance compared with the input one. Of course, this phenomenon does not contradict the causality principle. It is also worth emphasizing that the tested circuit respects all required criteria of classical active microwave devices such as gain, matching and stability. As predicted in theory (Ravelo et al., 2007a, 2007b, 2007c and 2008a), for a prototype implemented in planar technology, we have measured in time-domain a pulse peak advance of about -2 ns or 24% of the 1/e-input pulse half-width without attenuation. It is also interesting to note that through this experimentation, the input noise contribution did not destroy the occurrence of time-domain advance induced by the NGD active circuit. Moreover, in this chapter, thanks to the S21-magnitude form, the understudied NGD circuit is able to exhibit a pulse compression phenomenon with a possibility of amplification. Then, it should be worth using the presented NGD active topology to compensate for dispersion effects and especially to reduce the intersymbol interference in certain telecommunication channels. As a potential application of this NGD circuit, a new principle of frequency independent phase shifter is proposed. By cascading a classical transmission line with this NGD circuit, a constant phase value is obtained. The efficiency of this principle was demonstrated by measurement. Indeed, a constant phase value of 90°±5° was obtained within a 76% relative frequency band centred at about 1.5 GHz. The impacts of the PS parameter variations and sensitivity analysis are stated. The main benefits of this NGD active PS concerns its compactness and also the facility to generate very low group delay, and the broad band characteristics. Besides, a two-stage NGD PS was also designed; the simulation results showed a bandwidth enhancement of the constant phase up to 125%. Some fields of applications such as the design of broadband active balun for RF front end architectures are discussed. As ongoing research, design of reconfigurable devices dedicated to telecommunication applications is envisaged. Future investigations will be devoted to the design of NGD devices able to operate at higher frequencies through the use of distributed elements. In this optic, the implementation of MMIC devices based on distributed elements is envisaged.

Study and Application of Microwave Active Circuits with Negative Group Delay