We present radio maps of the historical supernova remnant G11.2 - 0.3 in the frequency range from 4.85 GHz to 32 GHz .
The integrated spectrum with \alpha = -0.50 ( S \sim \nu ^ { \alpha } ) is dominated by its steep spectrum shell emission ( \alpha \sim - 0.57 ) , although a flat spectrum core structure classifies G11.2 - 0.3 as a composite supernova remnant .
A radial magnetic field structure is observed .
An analysis of the multi–frequency polarization data results in highly varying rotation measures along the shell .
The percentage polarization is rather low ( \sim 2 % ) and we conclude that G11.2 - 0.3 is in the transient phase from free to adiabatic expansion .
The central flat spectrum component is partly resolved .
A compact radio source with an inverted spectrum likely coincides with the previously detected X–ray pulsar ( Torii et al . [ 1997 ] ) .
Two symmetric structures with flat radio spectra possibly indicate a bipolar outflow .
Combining available X–ray and radio data we conclude that G11.2 - 0.3 is likely the remnant of a type II supernova explosion with an early type B progenitor star .