The paper deals with the non-autonomous linear delay differential equation
where and are real scalars and is a continuous and non-oscillatory function defined on . The equation is referred to as pantograph equation, since in a simplified version it models the collection of current by the pantograph of an electric locomotive. The asymptotic properties of the solutions are in focus. The following condition on the growth of is imposed:
The main result of the paper says that if fulfills this condition and is eventually positive, then there exist real constants and , where , and a continuous periodic function of period such that
Here is the real part of the possible complex such that , and is the solution of the considered equation, such that
(the existence of such a sulution is proved in the paper). Though it is natural to distinguish the cases of the eventually positive and the eventually negative , it is shown that a resembling asymptotic formula is valid also in the case of eventually negative. Finally, using a transformation approach these results are generalized to equations with a general form of the delay.