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:

• the number of half-wavelengths across the width of the waveguide (rectangular waveguides).
• the number of radial variations (circular waveguides).

Figure 1. On the left, the reference vector is defined in the direction of the waveguide width. To the right, the reference vector is defined in the direction of the waveguide height.

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 with regards to which direction is for m or n.

If the reference vectors differ between ports, it results in a phase mismatch between the S₂₁ and S₁₁.

Figure 2. Two waveguide ports with equal reference directions (on the left) and two waveguide ports with opposite reference directions (to the right). For both these cases, the magnitude for S₁₁ and S₂₁ are identical. For the case where the reference directions differs, the phase for S21 differ by 180° from S₁₁.