6.1.9    Attenuation, S11, and SWR

QuickWave allows calculating the absolute value of the reflection coefficient (|S11|) in the considered part of the circuit. This feature is available in the 1D Fields window, after switching to space domain. The value of |S11| is calculated after placing the markers (cursors) in the maximum and minimum of the field component envelope line and activating S11 function.

Note that the reflection coefficient measured in this way at the input of the circuit should be equal to the value of S₁₁ calculated by the software in S-Parameters post-processing only in two cases:

• if only one port takes part in the S-parameters extraction,

• if more ports take part in the S-parameters extraction, but we have chosen Sk1 at reference planes post-processing and declared the circuit as nonreciprocal (in the post-processing configuration dialogue of the Input Interface).

When we calculate the S-parameters of N-port circuit with N>1 and one of the following choices made for post-processing:

• Sk1 at reference planes for the circuit declared as reciprocal,

• Smn at reference planes

the value of |S₁₁| will be automatically corrected for reflections at imperfect absorbing boundaries. Therefore it will not be equal the value shown by the envelope.

Let us additionally note that the envelope readings may produce lower values of |S₁₁| than the S-Parameters post-processing. This may happen due to limited mesh resolution, which may cause that the actual envelope minimum is not found because it does not coincide with any of the electric/magnetic component nodes.

The above feature is used in practise in User Guide 3D: Rectangular waveguide filter.

The same S11 function enables also calculation of the SWR if markers are placed at the maximum and minimum of the envelope line.

Another functionality, which is enabled in QuickWave, allows calculating the attenuation between two points in the circuit. This feature is available in the 1D Fields window, after switching to space domain and activating Attn function. The attenuation is calculated between two point indicated by the markers (cursors).

The above quantities may be calculated along any line parallel to one of the coordinate axes or along a user-defined contour.