Positive ion feedback can be problematic in a high precision Time Projection Chamber (TPC) as proposed for the International Linear Collider (ILC). Use of a traditional wire gating device would increase the dead areas in the planned module structure. F. Sauli proposed, in 2006, the use of a Gas Electron Multiplier (GEM) as a gating device. We have measured the electron transparency for a 14 mu m thick GEM in a 1 T magnetic field. The transparency does not meet the requirement for a TPC at the ILC. We performed a simulation study using Garfield++ to understand the important parameters. Simulations show that a new GEM structure with wider aperture, for example a hexagonal honeycomb structure, can improve the performance as a gate. Results of measurements will be compared to the simulation and the predicted performance of the new GEM structure will be described.