Design of microstrip lowpass filter with compact size and ultra-wide stopband

A new microstrip lowpass filter with compact size and ultra-wide stopband is presented. To achieve a compact design and ultra-wide band rejection, both triangular patch resonators and polygonal patch resonators are introduced in the filter. To reduce the circuit size of the filter further, the meander transmission line is also adopted in the design. A demonstration filter with 3 dB cutoff frequency at 0.85 GHz has been designed, fabricated and measured. Results indicate that the proposed filter is able to suppress the 14th-harmonic response referred to a suppression degree of 15 dB, together with a small size of 0.089 λ_g × 0.081 λ_g, where λ_g is the guided wavelength at 0.85 GHz.