Realization of practical lumped element all-pass networks for delay equalization

Summary form only given, as follows. All-pass networks of the second order used for delay equalization are described in various textbooks, but are frequently quite unrealizable due to impractical circuit element values. This problem has now been solved using network transformations, leading to simple design equations to derive the resulting practical networks. An example is given of an all-pass network used in the design of a delay-equalized filter having a passband from 1250 to 1500 MHz. The technique has been used to design many such equalized filters from VHF to microwave. They have the advantages of much smaller size and lower cost compared to internally equalized coaxial filters.