[en] An essential challenge in present fusion plasma research is the study of plasma turbulence. The turbulence behavior is investigated experimentally on the ASDEX Upgrade tokamak using Doppler reflectometry, a diagnostic technique sensitive to density fluctuations at a specific wavenumber k _{perpendicularto}. This microwave radar diagnostic utilizes localized Bragg backscattering of the launched beam (k₀) by the density fluctuations at the plasma cutoff layer. The incident angle θ selects the probed k _{perpendicularto} via the Bragg condition k _{perpendicularto} ∼ 2k₀sinθ. The measured Doppler shifted frequency spectrum allows the determination of the perpendicular plasma rotation velocity, u _{perpendicularto} =v_ExB+v_turb, directly from the Doppler frequency shift(f_D = u _{perpendicularto} k _{perpendicularto} /2π), and the turbulence amplitude from the backscattered power level. This thesis work presents a survey of u _{perpendicularto} radial profiles and k _{perpendicularto} spectrum measurements for a variety of plasma conditions obtained by scanning the antenna tilt angle. This was achieved by extending the existing V-band Doppler reflectometry system (50 - 75 GHz) with a new W-band system (75 - 110 GHz), which was especially designed for measuring the k _{perpendicularto} spectrum and additionally expands the radial coverage into the plasma core region. It consists of a remote steerable antenna with an adjustable line of sight allowing for dynamic wavenumber selection up to 25 cm ^-1 and a reflectometer with a 'phase locked loop' stabilized transmitter allowing for the precise determination of the instrument response function. The proper system functionality was demonstrated by laboratory testing and benckmarking against the V-band system. The new profile measurements obtained show a dependence of u _{perpendicularto} on the probed k _{perpendicularto}. The observations indicate that the shape of the turbulence k _{perpendicularto} spectrum is a significant factor in the u _{perpendicularto} measurement. The results also suggest that the contribution of the intrinsic turbulence phase velocity v_turb to the measured u _{perpendicularto} may not be negligible in some cases. The measured turbulence k _{perpendicularto} spectra exhibit the expected monotonic power fall-off with S(k₁) α k _{perpendicularto}^-α. For the low (L) confinement mode the spectral index is found to agree very well with previous results from other tokamak experiments with α ∝ 4. The measurements show that the transition from L-mode to high (H) confinement mode is accompanied by a reduction of the turbulence level. In H-mode the spectral index is observed to increase towards the core reaching comparatively high values with α ∝ 6 - 9. Altering the heating scenario by applying additional electron cyclotron resonance heating effects the k _{perpendicularto} spectra indicating a link between the plasma turbulence and the heating scheme. (orig.)