This paper presents a compact planar lowpass filter with super ultra-wideband (sUWB) passband and stopband for future possible sUWB radio system. The filter employs radial stubs to realize such sUWB passband and stopband and a sharp filter skirt performance. Design of the filter was based on electromagnetic simulation. The measured results of a 4-stage filter demonstrated the excellent filter performance: sUWB passband from DC to 22GHz with low insertion loss about 0.5dB at central frequency; sUWB stopband from 23 to 50GHz with attenuation larger than 35dB, which is the widest lowpass filter with widest stopband in the world, to the authors' best knowledge. The group delay over the passband is about 0.20ns and very flat. An sUWB bandpass filter with excellent bandpass and bandstop performance was also achieved and presented by integrating the developed sUWB losspass filter and an sUWB bandpass filter using broadside-coupled structure.