Design formulae for five low pass electrical networks are obtained. These design formulae are based on the concept of ``group delay time'' which represents the delay for a signal composed of a narrow band of frequencies. The dependence on the circuit parameters of the deviation of the group delay time from a constant value is investigated for a simple L‐C line, an m‐derived section, a type B compensating network, and for two other networks. The relative performance of these networks is discussed, and the properties of the image impedance are summarized briefly.