Compact microstrip triplexer based on coupled stepped impedance resonators

A new compact microstrip triplexer (2.4 / 3.5 / 5.8 GHz) using the coupled stepped impedance resonators (SIRs) is proposed. The triplexer is composed of three pairs of coupled SIRs with impedance ratio (K <; 1) and the source-load coupling lines. The resonant peaks can be easily determined by tuning the impedance ratio (K) and length ratio (α) of the SIRs so as to implement a 2-order bandpass filter individually. The source-load coupling lines are designed to correspond to the quarter-wavelength at the center frequency for each channel. The proposed triplexer is showing a simple configuration, an effective design method and a small circuit size.