Novel synthesized microstrip line with quasi-elliptic response for harmonic suppressions

A novel synthesized microstrip line with quasi-elliptic response is proposed in this paper. By utilizing quasi-lumped elements, the proposed synthesized lines are capable of reducing the circuit size with good slow-wave property. Benefitted from the quasi-elliptic response, signal suppression capability is introduced to the synthesized line at the harmonic frequencies. The design concept, circuit geometry, equivalent lumped circuit model, and simulated and measured results are carefully investigated and discussed. Based on the new synthesized microstrip line, a miniaturized quadrature hybrid coupler with harmonic suppressions is designed as a demonstrated example. The signal rejection levels are higher than 20 and 40 dB at the second and third harmonics, respectively. At the mean time, the size reduction percentage is 50%.