Dual‐Transmission‐Line Microstrip Equiripple Lowpass Filter with Sharp Roll‐Off

A novel application of a dual‐transmission line is proposed to design a lowpass filter (LPF). The proposed structure uses only transmission line elements to produce an equiripple LPF response with sharp roll‐off. Design equations are derived using a lossless transmission line model. Controlling the electrical lengths, three transmission‐zeros are realized in the stopband to obtain a sharp roll‐off rate and wide stopband bandwidth. A single unit microstrip LPF with a 3‐dB cut‐off frequency at 1.0 GHz having a roll‐off of 135 dB/GHz along with a stopband bandwidth of 69.5% is designed for validation.