Compact LPF With Sharp Roll Off and Wide Stopband Using Coupling Stepped Impedance Triangular Resonator

A lowpass fllter with sharp transition and wide stopband using a novel coupling stepped- impedance triangular resonator is presented. The L-C equivalent circuit is developed for designing this type fllter and analyzing the mechanism for improving roll-ofi and rejection property. The stopband width, passband edge, roll-ofi rate and overall suppression level are afiected by coupling capacitance. The efiect of coupling capacitance is analyzed using calculated frequency response. Coupling triangular stubs provide adequate coupling capacitance resulting in balance among transition property, stopband width and suppression level easily. A single LPF unit is designed and fabricated with cutofi frequency of 860MHz. The single LPF unit exhibits 40-dB suppression level from 1.11GHz to 2.28GHz. A cascaded LPF with three asymmetric units provides 40-dB suppression level from 1.1GHz to 6.76GHz, and roll- ofi rate of 154dB/GHz with compact size as small as 0:23‚g £ 0:05‚g, where ‚g is guided wavelength at cutofi frequency.