Miniaturization of hairpin resonator filters with improved harmonic suppression by using lumped capacitors

In this paper, we present a miniaturization technique of the hairpin resonator filters using lumped capacitors. The key concept is to use resonator dimensions at higher frequencies and then apply capacitive loading to achieve the desired resonant frequency. The proposed technique was verified through experimental work of a third-order Chebyshev type bandpass filter centered at 1 GHz. Up to 80% reduction in overall area can be obtained when the unloaded resonator resonates at three times the desired operating frequency. In addition to the reduction in the overall area, an improved suppression of spurious harmonic responses was also achieved attributed to the higher operation frequency of the unloaded resonators.