Compact Half-Mode Triple-Band Bandpass Filter by using Stepped Impedance Resonators with Grounding Via Holes

This letter presents a half-mode triple-band bandpass filter based on folded stepped impedance resonator stub. Also, an interdigital structure with lumped capacitance is added to the circuit to obtain a compact-size filter while maintaining the filtering characteristics. The utilization of the lumped capacitor at the middle point of the interdigital structure contributes to the shift down of the higher modes. Thus, an extra passband generates at the operating frequency range. Also, more reduced size is achieved by using a half-mode circuit.