# Reference Vector

The reference vector specifies the reference direction for a waveguide port.

The reference vector is indicated by a white line connecting the edge of a waveguide with the centre of the waveguide port and shows the direction of m, where m corresponds to:
• For a rectangular waveguide, the number of half-wavelengths across the width of the waveguide.
• For a circular waveguide, the number of radial variations.

For a rectangular waveguide, defining the reference vector in one direction, the dominant mode at a frequency might be TE10. Rotating the reference vector with 90° and solving the same problem, the dominant mode will be indicated as TE01.

For a circular waveguide, there is no ambiguity which direction is for m or n.

Note: Information given for the modes in the .out file corresponds to the specified direction of the reference vector.
If the reference vectors differ between ports, it results in a phase mismatch between the S21 and S11.