Sensitive radio continuum surveys of the Galactic plane are ideal for discovering new supernova remnants ( SNRs ) .
From the Sino-German \lambda 6 cm polarisation survey of the Galactic plane , an extended shell-like structure has been found at \ell = 21 \fdg 8 ,b = -3 \fdg 0 , which has a size of about 1 \degr .
New observations were made with the Effelsberg 100-m radio telescope at \lambda 11 cm to estimate the source spectrum together with the Urumqi \lambda 6 cm and the Effelsberg \lambda 21 cm data .
The spectral index of G21.8 - 3.0 was found to be \alpha = -0.72 \pm 0.16 .
Polarised emission was mostly detected in the eastern half of G21.8 - 3.0 at both \lambda 6 cm and \lambda 11 cm .
These properties , together with the H \alpha filament along its northern periphery and the lack of infrared emission , indicate that the emission is non-thermal as is usual in shell-type SNRs .