Allpass Phase and Group Delay Equalizer Networks

This chapter deals with the external allpass phase and group delay equalizers. It also presents a summary of the The lumped-element allpass networks as a background to the design of microwave allpass networks. Typically, lumped-element allpass networks are realized by symmetric lattice structures. The dissipation loss in allpass networks follows the same relationship as the filter networks. The shape of the group delays of allpass networks is nearly opposite that of the group delay of filter networks. In order to generate group delay tradeoffs, the chapter considers a C-, D-, and CD-section allpass networks to equalize the delay of the channelizing filter. For computing the physical dimensions, the D-section equalizer is chosen since it provides the most efficient practical equalizer network. The chapter concludes with a brief discussion of the relative merits of external equalizers versus linear phase filters.