In manuscript Am. B. 340 Karges writes "J.P." below the the title of this composition. And in this case it is certain that he means Jan Pieterszoon Sweelinck, as this piece is based on Sweelinck's Echo Fantasia d4, SwWV 261. The first 14 bars are (almost) identical to Sweelink's original, After those 14 bars Karges creates a different piece using the elements of Sweelink's original. One characteristic in Karges' adaptation is that he shortens the echo of long phrases, where Sweelinck just writes an equally long echo. And where Sweelinck ends his Fantasia with an ascending scale, Karges writes a descending scale, all the way down to D in the great octave.
Score available here: http://partitura.org/index.php/wilhelm-karges-jan-pieterszoon-sweelinck-fantasia-in-d