  In this paper, we present a method for analysis of phase errors and power
truncation in SiGe/Si graded index arrayed waveguide gratings (AWGs) operating
in mid-infrared spectral range. Semi-analytical model used herein is based on
Gaussian approximation of the modal field and Fourier Optics. This method is
applied to study the correlation between crosstalk level, effective index
deviation in array waveguides and power truncation in 3.4 micrometer, 4.5
micrometer, 5.7 micrometer and 7.6 micrometer central wavelength AWGs. We show
that the impact of effective index variation is more critical for AWGs with
smaller operational wavelengths and power truncation should not exceed 5% for
these types of devices. In conclusion, we refer to experimental data of 4.5
{\mu}m, 5.7 {\mu}m and 7.6 {\mu}m central wavelength AWGs where a cross talk
level of 24 dB is obtained, corresponding to relative errors of effective
indices and equivalent path length deviations respectively lower than 2 10-5
and of 0.2 micrometer in 10 mm length of the devices.
