Harmonic-suppression LTCC filter with the step-impedance quarter-wavelength open stub

An effective method to design a low-temperature co-fired ceramic RF bandpass filter with suppression of the harmonic frequency is demonstrated in this paper. The second harmonic, which appears in the frequency band of 4.8-5.0 GHz, is very significant and should be reduced in the 2.4-GHz wireless local area network and Bluetooth application. This feature of harmonic frequency suppression is very important in a communication system to improve linearity, output power, intermodulation performance, etc. The harmonic-suppression filter can be easily obtained by adopting the characteristic of equivalent quarter-wavelength resonators. The detailed three-dimensional layout of each layer is disclosed. By analyzing the influences of the dielectric constant and layer thickness of a ceramic sheet by electromagnetic simulation, the optimal condition for the filter design can be obtained. The measured results agree well with the simulation.