The Karlsruhe Tritium Neutrino (KATRIN) Experiment aims to measure the effective electron antineutrino mass with a sensitivity of 200 meV (90 % C. L.) by analysing the kinematic endpoint of the tritium beta-electron spectrum. In this thesis, the systematic effects of KATRIN are evaluated. Since most of them are linked to the tritium source, the source cryostat performance is fully characterised in this work. With a dedicated measurement campaign performed with krypton-83m, energy scale-related systematic effects are investigated and the great capabilities of KATRIN in high-resolution spectroscopy of keV-scale electrons are demonstrated
