This paper studies a very simple structure for dual-band bandpass filter. Filter is composed of two asymmetric coupled resonator circuit by two sets of different size stepped impedance resonator. This circuit applied microstrip line, coupling principle and impedance ratio by controlling the stepped impedance resonator to control the center frequency 2.6/5.2 GHz of the first and the second bandpass filter. The basic structure of the filter is constituted by the three sections of transmission line and two sets of SIR, that is, in two gaps of the three sections of transmission line parallel connection the equivalent inductances and capacitor of the two sets of SIR in series with the resonant circuit (LCL) to constitute bandpass filter. The low frequency 2.6 GHz is through the upper half of low impedance SIR, and the high frequency 5.2 GHz is through the lower half of high impedance SIR. This paper presents the design of asymmetric SIR-based dual-band bandpass filter, the filter structure is simple, easy to produce and can control the characteristics of the passband center frequency. By electromagnet simulation software( IE3D ) to simulate, the actual production of the circuit using a vector analyzer measurement, simulation and measurement results show good consistency.
Harmonic suppressed coupled stepped-impedance resonator based dual-band tunable bandpass filter
