Limit Line

The Limit Line (accessed via Plot|Limit Line) is an optional trace that visualizes a predefined limit value of a measured quantity (e.g., a minimum or maximum accepted value). A single limit line with a user-defined appearance (color, width and style) can be displayed on the screen. In rectangular plots, the limit line is a straight line parallel to the x‑axis. In circular plots, the limit line is a circle centered at zero reflection coefficient.

Generally, each display type in each particular display window has its own individual limit line, defined by its presence, appearance and value.

An exception is the reflection coefficient in a given display window, where the limit value is linked to the format in which the reflection coefficient is displayed. When changing the display format, both the reflection coefficient and the limit value are converted using the same formulas.

The group of display types corresponding to reflection coefficient includes the following:

Mag,  LogMag,  VSWR,  Polar,  Z-Smith,  Y-Smith,  Oven

So, for instance, when you define the limit value 0.1 in Mag format and change the display to LogMag, the limit line appears at the level of –20 dB, which is 20*log(0.1). When you switch to VSWR, the limit line value becomes 1.222, which is (1 + 0.1)/(1 – 0.1). In circular formats, the limit line appears as a circle with the radius of 0.1.

• To show and hide the limit line, click the Plot|Limit Line|Visible menu item.

• To change the limit line value, click the Plot|Limit Line|Value menu item and enter a new limit value. This also makes the limit line visible.

• To change the limit line appearance, click the Plot|Limit Line|Style menu item. The dialog box titled Limit Line Properties opens. Select the desired Color, Width, and pick a Style. Press OK.