Exploring Negative Group Delay in Passive Microwave Circuits

Abstract

Group delay is an important factor of consideration while designing a circuit with minimum signal distortion. There have been various attempts to minimize this group delay using different techniques, one of such techniques is to introduce Negative Group Delay (NGD) in the circuit to compensate for the positive group delay and to reduce group delay variability in pass band. In this project, in order to explore and study NGD phenomenon, we studied and implemented, based on published work, two passive circuits having negative group delay characteristics. First circuit having NGD characteristics is O=O shaped circuit which consists of a power divider and a power combiner. It produced an NGD of -0.995 ns and S11 of -18.6 dB. The circuit produced NGD without using any resistors while operating at 1.2 GHz. Second circuit is a power divider operating at a center frequency of 1.8 GHz. The PD circuit incorporates a resistor and coupled line structure that provides matching and NGD characteristics. This circuit was designed using the technique reported by Girdhari Choudhary et. Al. [18] but for operation at a different frequency and using a different substrate. The PD was implemented on FR-4 substrate with a height of 40 mils and it produced excellent matching with S11 = -21 dB and NGD was measured to be -2.6ns at 1.8 GHz frequency. In order to investigate the effect of substrate height, another Power Divider was designed and implemented on a substrate of height 31 mils. For this circuit, the measured NGD was -0.8ns and S11 = -26 dB. These results show that an increase in the height of substrate results in a higher value of NGD which may be attributed to higher losses suffered by the circuit fabricated on a substrate of larger height.