You might be tempted to draw a pattern manually and use the SUPERHATCH command, but that creates a block, not a true native pattern. Native PAT files are superior because they are lightweight, memory-efficient, and scale infinitely without increasing file size.
Converting repeatable DWG geometry into a hatch pattern significantly reduces file size compared to copying and pasting hundreds of individual lines. Top Methods for DWG to PAT Conversion dwg to pat converter
Free, customizable, integrates directly into AutoCAD. Cons: Can be buggy with complex geometry; requires cleaning up the geometry (exploding blocks, removing curves) before running the script. You might be tempted to draw a pattern
They "tessellate" the arc—breaking it into hundreds of tiny straight lines that look like a curve from a distance. If a converter does not offer a "tessellation tolerance" setting, your circles will look like hexagons. Top Methods for DWG to PAT Conversion Free,
A .pat file is essentially a text file defining a repeating tile. A converter analyzes your DWG geometry within a defined bounding box (typically a square from 0,0 to 1,1 or 0,0 to 100,100 ), calculates the repeating vectors, and exports the standardized code.
While AutoCAD does not have a direct "Save as PAT" button, you can use the Express Tools.