Design of microstrip lowpass filter with wide stopband and sharp roll-off using hexangular shaped resonator

A compact lowpass filter using a hexangular shaped resonator is presented. The designed lowpass filter has a -3 dB cutoff frequency of 2.97 GHz. The stopband bandwidth for the attenuation level of -20 dB is from 3.32 GHz up to 21 GHz, and the circuit only occupies 10.04 × 10.92 mm². The structure is simulated, fabricated and measured. Both simulation and measured results are presented and compared and there is good agreement between them. The insertion loss in the passband is <;0.06 dB and the fabricated filter presents a sharp transition band from 2.97 to 3.32 GHz for the attenuation level of -3 and -20 dB, respectively.