Low-temperature co-fired ceramic coupled-line bandpass filter design

A third-order multilayer coupled-line bandpass filter is presented. Four quarter-wavelength coupled-lines are interconnected to form three half-wavelength resonators and are arranged in such a way the overall filter will present a third order bandpass response with compact size. The impedance of the multilayer asymmetrical coupled-lines used in the topology was characterized for the low-temperature co-fired ceramic technology prior to the design to simplify the determination of the line width and gaps of the coupled-lines. The proposed filter is centered at 5 GHz and achieves a fractional bandwidth of 40%.