  We present radio continuum and linear polarisation observations of the pulsar
wind nebula CTB87 (G74.9+1.2) with the Effelsberg 100-m radio telescope between
4.75 and 32 GHz. An analysis of these new data including archived low-frequency
observations at 1420 MHz and 408 MHz from the Canadian Galactic Plane Survey
shows that CTB87 consists of two distinct emission components: a compact
kidney-shaped component, 14 pc x 8.5 pc (7.8' x 4.8') in size and a larger
diffuse, spherical and centrally peaked component of about 30 pc (17') in
diameter. The kidney-shaped component with a much steeper radio continuum
spectrum is highly linearly polarised and likely represents a relic pulsar wind
nebula. The diffuse component represents the undisturbed part of the PWN
expanding inside a cavity or stellar wind bubble. The previously reported
spectral break above 10 GHz is likely the result of missing large-scale
emission and insufficient sensitivity of the high-frequency radio continuum
observations. The simulation of the system's evolution yields an age of about
18,000 years as the result of a type II supernova explosion with an ejecta mass
of about 12 solar masses and an explosion energy of about 7 x 10^50 erg. We
also found evidence for a radio shell in our polarisation data which represents
the blast wave that entered the molecular cloud complex at a radius of about 13
pc.
