Lithographic Apparatus Having an Encoder Type Position Sensor System

A lithographic apparatus, comprising:

• a substrate table constructed and arranged to hold a substrate;
• an encoder sensor system for measuring a position of the substrate table, comprising an encoder sensor head and an encoder sensor target;
• and
• a reference structure configured to define a recess at least partially within the reference structure, configured and arranged to prevent a gas stream along at least part of the encoder sensor target.