Miniaturized microstrip ring filter

Miniaturized microstrip ring filter is presented. Four lumped capacitors are added in the initial ring resonator topology to shift the resonant frequency to about 50% of its nominal value, leading to size reduction of the filter. The required value of the capacitors is calculated using tuning synthesis equations of the ring resonator. The passband response of the filter is improved by modifying the line impedance of the ring. The final layout of the miniaturized filter centered at 2.76 GHz is compared to its counterpart showing a size reduction of about 67%.