What is the difference between the gap port and the gap (coax) port in HFSS 3D Layout?

he gap port is a type of edge port similar to a "lumped port" in regular HFSS. Gap ports are typically used to connect microstrip traces to a ground reference. They are simpler in structure compared to coaxial ports and are often used in planar designs. 

The Gap (Coax) Port, on the other hand, is used to excite terminals at package interfaces, such as vias, bondwires, and solder balls. It creates a circular geometry that resembles a coaxial conductor and is particularly useful for applications requiring a coaxial cross-section, providing a more complex and detailed representation of the port’s geometry.