  We have simulated the performance of the Josephson Travelling Wave Parametric
Amplifier (JTWPA) based on the one-dimensional array of RF SQUIDs. Unlike the
ideal model in which all SQUIDs are assumed to be identical, we allowed
variation of the device parameters such as the geometric inductance of the
SQUID loop, capacitance to ground, Josephson junction capacitance and critical
current. Our simulations confirm the negative effects of variation of the
device parameters leading to microwave reflections between individual cells and
the shift of the flux bias from the optimal point. The strongest effect is
caused by the variation of the geometric inductance as it varies both the wave
impedance and the flux bias. The most detrimental, however, are point defects,
such as shorts to ground making the circuit opaque to microwaves. This imposes
stringent requirements on the fabrication process making it extremely
challenging. We highlight the strict limitations on parameter spread in these
devices while also discussing the robustness of the scheme to variation
