  A Time Projection Chamber (TPC) using micro-pattern gas detectors is planned
as the main tracking device for a detector at the next Linear Collider. A novel
support structure for Gas Electron Multipliers (GEMs), which minimizes the
material and improves the flatness of the foils, has been developed and tested
with multiple GEM modules in a large TPC prototype at DESY. Reducing dead
material at the GEM module boundaries improves the field homogeneity. In
addition, it was shown in simulation that a field shaping ring at the border of
the module can improve the charge collection in regions with non-homogeneous
fields. This shaping wire was integrated into the module design and a
successful test beam campaign with three modules has been carried out. First
results regarding resolution and field distortions will be discussed.
