The spectral-angular and the linear polarization properties of channeling radiation emitted by 30.8 MeV electrons incident on a 13 μm thick silicon crystal at small angles with respect to various major crystal axes have been investigated. The transition from axial to planar channeling radiation properties is well described by a two-dimensional many-beam calculation based on a periodic string potential. At energies above the strongest planar channeling radiation lines coherent bremsstrahlung linearly polarized perpendicular to the polarization of the corresponding planar channeling radiation is observed and found to be well reproduced by the model calculations. Axial channeling radiation of the 〈110〉 axis shows a small amount of linear polarization due to the `double-well' potential in agreement with the calculations.
