Display Windows

Display windows (Fig. 16) are primary means of presenting measurement results graphically (as curves or dots) in selectable formats. When you start measurement, all open display windows will reflect the measured data in their corresponding formats.

Display Speed Considerations

As the measurement progresses, the windows are updated point-by-point. Please be aware that the operating system needs a relatively long time for this process (this also applies to the Results windows). Therefore, the more windows are open, the slower the process may be. If you observe that the display is lagging behind the actual data, try to open as few windows as possible.

Fig. 16.  Display windows with (a) rectangular plot and (b) circular plot.

Main Elements of Display Windows

Main elements of the display window include:

  • Plot

  • Legend

  • Menu

  • Toolbar

  • Limit Line

Plot

There are two types of display window plots:

  • Rectangular plots (example in Fig. 16a)

  • Circular plots (example in Fig. 16b)

Rectangular plots display a scalar measured quantity (e.g., incident power or modulus of reflection coefficient) as a function of the “Points” number, i.e., the sequential number of a received measurement data block. The number is related to time although there is no proportionality (measurement start instant and measurement duration may vary widely). The number of displayed points can be selected; on reaching this maximum, the displayed curves retrace and start from the beginning. Due to this, the measurement process is (somewhat inaccurately) referred to as sweeping.

Circular plots display the complex reflection coefficient in the form of a locus, enabling the user to observe both magnitude and phase simultaneously. Circular plots include the Polar plot (shown in Fig. 16b), the impedance Smith chart, the admittance Smith chart and the Oven plot.

The traces in the display windows are updated point by point as the measured data arrive.

Legend

The Legend is a small rectangle within the display window, showing the name and drawing attributes (appearance) for each displayed trace. To show and hide the Legend, click the Plot|Legend menu item. To change the appearance of the traces, click the button or the Trace|Properties menu item, or right-click the Legend box. See more details in section Trace Properties.

Menu

See section Display Window-Related Menu.

Toolbar

The display window toolbar contains buttons corresponding to frequently used menu commands:

    Trace properties

    Set scales

sbAutScale    Autoscale

Dflt  Set default scales

    Clear screen

    Redraw last trace

sbClear    Clear screen before measurement start (also referred to as Clear and Go)

sbPersist    Persist

    Show Input reflection coefficient (dimmed when not selected)

    Show Load reflection coefficient (dimmed when not selected)

Limit Line

The Limit Line (Plot|Limit Line) is an optional trace that visualizes a predefined value (e.g., tolerance) of the displayed quantity. You can modify its presence, appearance, and the associated value. The Limit Line is a straight line in rectangular plots and a circle in circular plots.

Display Windows-Related Commands

To open a new display window:

Click the Window|New Display menu item or the button. The window is, apart from its size and screen position, a replica of the currently active display window. Now, you can modify its settings as required.

When you close all display windows and then open a new display window, the new window will be the replica of the display window that was deleted last.

To activate an open display window:

Click into it. Settings made by menu items associated with display windows (Display, Scale, Trace, Plot) affect only the currently active display window.

To position and resize a display window:

Use standard Windows mouse-dragging techniques.

To close a display window:

Click the standard closing button. To close all display windows, click the Window|Close All Displays menu item.

When you close all display windows and then terminate the program, a single display window with default settings will open on the program restart.

Display Window-Related Menu

Each display window has its own menu. The menu is, however, merged into the main HomSoft menu. The display menu items (appearing as subitems of the main menu) are

Display,  Scale,  Trace,  Plot

Settings made in these menu items affect only the currently active display window.

Display

The Display menu is used for selecting the format and, if applicable, the units in which results will be shown. Available formats are:

  • Mag: Linear reflection coefficient magnitude M = |G|. For passive loads, magnitude lies between zero (perfect match) and 1 (total reflection).

  • LogMag: Logarithmic reflection coefficient magnitude L = 20 log(M) expressed in decibels (dB). A perfect match corresponds to L = -¥; total reflection corresponds to L = 0 dB.

Note that the return loss R is the negative of LogMag: R = –L.

  • VSWR: Voltage standing wave ratio V = (1+M)/(1–M).

  • Phase: Phase of reflection coefficient in degrees.

  • Polar: Polar plot, displaying reflection coefficient as a vector in complex plane.

  • Z-Smith: Impedance Smith chart, mapping complex reflection coefficient to normalized impedance

z = (1 + G)/(1 – G)

  • Y-Smith: Admittance Smith chart, mapping complex reflection coefficient to normalized admittance

y = 1/z = (1 – G)/(1 + G)

  • Oven: An alternative form of polar plot, rotated counter-clockwise by 90o and showing circles of constant VSWR. This form is often used for plotting Rieke diagrams of magnetrons.

  • Power: Incident, reflected and absorbed power in linear scale. Available units:

  • uW    microwatts

  • mW    milliwatts

  • W    watts

  • kW    kilowatts

  • LogPower: Incident, reflected and absorbed power in logarithmic scale. Available units:

  • dBm    decibels relative to P0 = 1 mW

  • dBW    decibels relative to P0 = 1 W

  • dBkW    decibels relative to P0 = 1 kW

    LogPower (LP) is related to linear power P by LP = 10 log(P/P0).

Scale

The Scale menu is used for scaling the active display window plot. The menu items are

Set Scale,  Autoscale,  Default

See Plot Scaling for more details.

These commands are more comfortably accessible via display window toolbar buttons.

Trace

The Trace menu is used for defining the appearance of traces drawn in the active display window and for switching between the measured and deembedded reflection coefficient. The menu items are

Properties,  Show Load

(the Show Load menu item appears only for the reflection coefficient-related displays). See details in sections Trace Properties and Input and Load Reflection Coefficients, subtopic Deembedding. The commands are more comfortably accessible via display window toolbar buttons.

Plot

The Plot menu groups commands associated with the overall plot appearance rather than with individual traces. The menu items are

Legend,  Limit Line, Clear, Clear and Go,  Persist

For their descriptions, see Main Elements of Display Windows, Limit Line, and Trace Properties.