specifications for the return losses are 20 dB. For the above data, the insertion loss at infinite frequency is 22.76 dB, corresponding to IKI =0.0364174 or JKI =27.4594006 (1). According to (4), for N = 4 there are 60 different networks. Fig. 1 shows three possible implementations for three different positions of the K inverter and the same order in the extraction of the poles corresponding to transmission zeros at w ~, w * , w ~ and w4. All the circuital values are collected in Table 0 IEE 2003