  The advancement of 3D-printing opens up a new way of constructing affordable
custom terahertz (THz) components due to suitable printing resolution and THz
transparency of polymer materials. We present a way of calculating, designing
and fabricating a THz waveplate that phase-modulates an incident THz beam
({\lambda}=2.14 mm) in order to create a predefined intensity profile of the
optical wavefront on a distant image plane. Our calculations were performed for
two distinct target intensities with the use of a modified Gerchberg-Saxton
algorithm. The resulting phase-modulating profiles were used to model the
polyactide elements, which were printed out with a commercially available
3D-printer. The results were tested in an THz experimental setup equipped with
a scanning option and they showed good agreement with theoretical predictions.
