  Radio telescopes are used to accurately measure the time of arrival (ToA) of
radio pulses in pulsar timing experiments that target mostly millisecond
pulsars (MSPs) due to their high rotational stability. This allows for detailed
study of MSPs and forms the basis of experiments to detect gravitational waves.
Apart from intrinsic and propagation effects, such as pulse-to-pulse jitter and
dispersion variations in the interstellar medium, timing precision is limited
in part by the following: polarization purity of the telescope's orthogonally
polarized receptors, the signal-to-noise ratio (S/N) of the pulsar profile, and
the polarization fidelity of the system. Using simulations, we present how
fundamental limitations in recovering the true polarization reduce the
precision of ToA measurements. Any real system will respond differently to each
source observed depending on the unique pulsar polarization profile. Using the
profiles of known MSPs we quantify the limits of observing system
specifications that yield satisfactory ToA measurements, and we place a
practical design limit beyond which improvement of the system results in
diminishing returns. Our aim is to justify limits for the front-end
polarization characteristics of next generation radio telescopes, leading to
the Square Kilometre Array (SKA).
