Reduced-sized single coupled-line low pass filter

A low pass filter consisted of one inner- connected coupled-line and two open-stub transmission lines possessed quasi-elliptic frequency response and wide rejection bandwidth is proposed. The analysis is based on transmission line and coupled- line circuit model. Two-port impedance matrices were derived and a T type equivalent circuit was obtained. Based on this equivalent circuit, a circuit with 3 dB cutoff frequency at 2.45 GHz was designed, simulated, and measured. The simulated and measured results are in good agreement within 12 GHz.