2020 Volume 13 Pages E19-016-1-E19-016-13
For realizing stable and high-speed communication systems, the spectral of signals need to be purified, thus, an asymmetric third-order bandpass filter, which composed by open-circuited stubs loaded dissimilar stepped impedance resonators, is proposed to realize 20 dB stop-band attenuation up to 20.6f0 (17.85 GHz). Open-circuited stubs are loaded to resonators for scattering harmonics and suppressing the unexpected harmonics. Asymmetric coupling structure has been applied to suppress the harmonics and the inevitable fly-over coupling between resonators. Stepped impedance resonators are designed with extremely low impedance ratio (Rz) for enhancing the open-circuited stubs and asymmetric coupling structures' suppression on harmonics and reducing the circuit size. Resonance frequencies, external quality factor (Qe) and coupling coefficient (K) between dissimilar resonators have been synthesized and derived by admittance analysis. The open-circuited stub and K's influence on fundamental resonance, and Qe have been derived by equations and investigated by simulations respectively. Both the calculations and simulations show that the open-circuited stub and asymmetric coupling structure influence fundamental resonance little while the harmonics significantly.
