Design of compact microstrip low-pass filter with analytical sharpness of transition band

A novel microstrip low-pass filter (LPF) using radial patched resonator and modified T-shaped resonators is designed to achieve ultra-wide stop-band. Also, the designed LPF has successfully addressed the problems of compactness and insertion loss, simultaneously. LC equivalent circuit of the proposed filter is calculated and equation for the sharpness in transition band is obtained based on LC equivalent circuit and transfer function. The proposed filter not only exhibits a very wide stop-band of 168%, but also is able to suppress the 11th-harmonic response in conjunction with a small size of 0.147 × 0.052λg, where λg is the guided wavelength at 1.47 GHz. It is shown that the simulated results are highly consistent with the measured data.