Abstract: A compact lowpass filter with ultra sharp rejection and wideband suppression is proposed in this paper. Each section is composed of a microstrip line and an inter-digital capacitor. Based on the theoretical analysis of the single section,one could easily achieve the passband limit with good selectivity. To further improve the stopband performance, a periodically cascaded section structure is employed, which leads to multi transmission zeros to suppress the spurious. To verify the mechanism above, a filter is designed and fabricated. The measured result shows good insertion loss less than -0.9 dB over 95% of the passband and return loss is below -13 dB. Measured passband to stopband attenuation slope is 160 dB/GHz. Specifically, the proposed filter possesses a stopband up to 13.1 GHz with a satisfactory rejection greater than -20 dB.