Homer Model Window

The parameters of the simulation are set in the Homer Model window (Fig. 47), which is always open in the main program window. The window contains three pages (tabs), titled DUT, Animation, and More.

The speed of generation of all simulated “measurements” is controlled via the Pause edit in the Animation page. A wait period proportional to Pause setting is inserted between each consesutive measurement. The number does not represent any real time unit and you have to experiment to arrive at a reasonable sweeping speed (starting with 1000 is a good choice).

New settings are not accepted until you click the  Apply  button (an exception is the Error Byte setting on the Errors page, which takes effect immediately).

DUT Page

The DUT page (Fig. 47) controls the reflection coefficient of the simulated load (DUT stands for Device Under Test).

Fig. 47.  Homer Model window: DUT page.

Type of DUT

The Type group of radio buttons selects the type of the simulated DUT. The choices are:

  • Defined: The DUT reflection coefficient GA is defined by the values of magnitude and phase in the Defined Reflection Coefficient box.

  • Match: The DUT reflection coefficient GA is zero (perfect match).

  • Animated: The DUT reflection coefficient magnitude and phase is automatically incremented point-by-point as defined in Animation page.

  • Plot: The DUT reflection coefficient GA is comfortably generated by mouse clicking and dragging in a polar plot. See topic Plot for details.

Add Line Length

If the Add Line Length checkbox is checked, then a waveguide with length L defined in the adjacent edit box is connected between the DUT as defined above and the Autotuner output flange. This allows the user to simulate the influence of such a waveguide on the autotuning performance. For the underlying theory, please refer to the topic How Long Is Too Long. Based on this theory, the load reflection coefficient as seen at the Autotuner output is GL. If the Add Line Length checkbox is not checked or L = 0, then GL = GA.

A note on load reference plane:

The load reflection coefficient GL discussed here refers to the Homer’s default load reference plane. This plane coincides with the output flange of the device. See also: Input and Load Reflection Coefficients, Deembedding and the Plane Ext item of the Homer Menu.

Uncertainty Radius

A nonzero value of the Uncertainty Radius adds random noise to the generated reflection coefficient. The noise is added as a random vector to the simulated complex reflection coefficient. The noise vector is a complex number with arbitrary random phase and a random magnitude not exceeding the Uncertainty Radius. The resulting uncertainty circle is best observable in the Polar plot format. For useful Polar plot settings, see Tips for Circular Plots in the Trace Properties section.

If the mode of signal sampling (Waveform) is set to CW, increasing the sample count Ns (i.e., the voltage averaging number) decreases the displayed noise level as in real measurement. Fluctuations equal exactly to the Uncertainty Radius are only observable when the averaging is set to unity. To modify the averaging:

  • Set Waveform to CW (click  CW  Signal toolbar button (Fig. 15), or use the Homer Sampling Setup window).

  • Modify the sample count (averaging) by editing Sample Count in the Homer Sampling Setup window or by clicking the sbNsampl button.

Case of Rectified and Pulsed modes of sampling

Please note that (unlike a real Homer device) this CW sample count setting also affects data fluctuations simulated in Rectified and Pulsed modes.

Defined Reflection Coefficient

When selecting the Defined radio button in Type group, you can define the simulated reflection coefficient by editing the values in Magnitude and Phase edit boxes. To define the reflection coefficient:

  • Click the arrow to the right of the Magnitude edit to open a drop-down list and pick the format in which you wish to define the reflection coefficient magnitude (Mag=linear, dB=logarithmic in decibels, or VSWR=voltage standing wave ratio).

  • Type the desired value in the Magnitude edit box. Note that when you select a different format, the entered value is automatically converted to the new format so that it represents the same reflection coefficient.

  • Type the phase angle value in degrees in the Phase edit box or step it by clicking the associated UpDown control.

  • Press the  Apply  button.

Plot

When clicking the Plot radio button in the Type group, followed by the  Apply  button, the window titled DUT Reflection Coefficient (Fig. 48) will open, containing a polar plot. You are now able to generate the simulated Device Under Test (DUT) reflection coefficient GA by the following methods:

  • Clicking into the plot.

  • Dragging the cursor over the plot by holding down the left mouse button.

  • Typing in the two edits below the Polar Radius panel (left: linear magnitude, right: phase in degrees), then clicking the Apply button or hitting the Enter key on the keyboard. Invalid inputs are ignored and substituted by the previous values.

Fig. 48.  DUT Reflection Coefficient window. Right: Matchable area valid for the chosen simulation frequency and maximal stub insertions.

Mouse-generated reflection coefficients are displayed numerically in Mag and Deg edits. The magnitude is also converted to VSWR.

To change the plot radius (to zoom into the plot), click one of the Polar Radius radio buttons.

Note: If you now select another type of DUT simulation (Defined, Match, or Animated) the plot disappears.

Realizable and Matchable Areas

In addition to conveniently generating reflection coefficients, the DUT Reflection Coefficient window enables you, in the form of an underlying graphic:

  • To see the area of reflection coefficients realizable by your tuner at the simulation frequency; i.e., the range of the tuner input reflection coefficients that can be obtained by any combination of settings of stubs 1+2 (blue-bordered area) and 2+3 (pink-bordered area) for a tuner terminated by a match (zero reflection coefficient). To show the realizable area, click Realizable radio button in the Show Area group. You can compare this area with the area obtained in the Polar plot by moving the stubs while “measuring”.

  • To see the area of reflection coefficients matchable by your tuner at the simulation frequency; i.e., the range of load reflection coefficients that can be matched by proper positioning of stubs 1+2 (blue-bordered area) or 2+3 (pink-bordered area), respectively. To see the area of matchable reflection coefficients, click Matchable radio button in the Show Area group. You can observe the effect of changing reflection coefficient while “measuring” with autotuning switched on. The best suited display format is Polar or other circular plots.

The realizable and matchable areas can be referred to different reference planes, selected in Refer Area to group. The most natural choice for the matchable area is Output, which means the plane of the tuner output flange. The reference plane can also be shifted to the axis either of Stub 3 or Stub 1, or to the reflectometer calibration plane (Cal). The plane positions are specified on the Sketch page (Fig. 37) of the System Info window. The most natural choice for the realizable area is Stub 1.

A special choice of the reference plane is Transform. This relates the areas to the input of a two-port network connected at the Homer input. For details, see section Transforming Input Reflection Coefficient. The Transform choice is only meaningful for the realizable area. If the transform is not active, the areas refer to Stub 1 (no network connected).

The tuner model and frequency for the displayed areas are shown at the bottom of the plot. The associated maximum stub insertion is shown at the top right.

You can export the area borders as a contour to a text file in the user folder. To do so, click the  E  button (bottom right).

Animation Page

The Animation page (Fig. 49 left) allows the reflection coefficient magnitude and phase to be stepped automatically between Start and Stop values with Step increments. The whole pattern can be offset by defining Center coordinates.

The animation can be activated by clicking the Animated radio button on the DUT page or by selecting the Animation page, and then clicking the  Apply  button.

Two example animations are shown in Fig. 49.

  

Fig. 49.  Animation page of Homer Model window (top) and the resulting evolution of load reflection coefficients (bottom).

To obtain these plots, set Homer|Points per Sweep = 101, check Homer|Finish Sweep, set Type = Animated on the DUT page, click  Apply  , then start measurement and stop it before the end of the sweep. Autotuning must be switched OFF and the tuning stubs retracted.

  • The Center, Start and Stop values for magnitude can be adjusted in 1% (0.01) increments via the up-down control; the Center, Start and Stop values for phase can be adjusted in 1° increments. They can also be entered manually.

  • The Step values can be picked from the drop-down lists, or edited arbitrarily; they will be rounded off.

  • The Start value may be lower than, greater than, or equal to the Stop value. If, for instance, Start = 360° and Stop = 0° for phase, the reflection coefficient will rotate clockwise.

  • When the R (Reverse) checkbox is unchecked, then, on reaching the Stop value, the corresponding parameter jumps back to its Start value and the process continues.

  • When R is checked, then, on reaching the Stop value, the parameter only changes its step direction and starts stepping back to the Start value.

  • When the Do not spiral checkbox is checked, the magnitude remains constant irrespective of the magnitude Stop or Step settings. Thus, you can model load reflection coefficients moving along a circle or an arc.

  • If the sweep is interrupted, the next sweep continues from the current parameter values. To initialize the animation (also while sweeping), click the  Apply  button.

  • The stepping speed is controlled by the Pause edit.

  • To make more than one “measurement” at each reflection coefficient setting, increase the Meas/Posit count.

Note about display periodicity

To obtain stable, periodically repeated plots, consider this:

Let the magnitude Start, Stop, and Step values are M1, M2, and DM. Then the repetition period of the magnitude is

nmag = 1 + |(M2 – M1)/DM|

Let the phase Start, Stop, and Step values are j1, j2, and Dj. Then the repetition period of the phase is

npha = 1 + |(j2 – j1)/D j|

Let the Homer|Points per Sweep setting is Npts.

To obtain stable, periodically repeated plots, the following conditions must be satisfied:

nmag = k1 npha

Npts = k2 nmag

where k1 and k2 are integers. (This assumes that nmag > npha and Npts > nmag.)

Note that the settings in Fig. 49 do not meet these conditions because nmag /npha = 5.611.

More Page

The More page (Fig. 50) defines the simulated signal frequency, generated power, and Homer internal temperature. Power-related bits of Error Byte can also be defined.

Fig. 50.  More page of Homer Model window.

To define simulated frequency:

  • In the Frequency edit box, type the value in MHz or use appropriate prefixes (e.g., G or g for Giga).

  • In the Uncert. (Uncertainty) edit box, enter the frequency uncertainty (random variation as a percentage).

  • Press the  Apply  button.

Notes:

  • A Substitute Frequency warning may be triggered, depending on these settings and the Homer|Freq Toler setting.

  • If the user attempts to set the simulated frequency too far (more than ± 10%) from the nominal frequency, the nominal frequency will be used instead.

  • The error conditions are best observed in the full-size Results window.

To define simulated incident power:

  • Enter the value in kilowatts in the Inc. Power edit box.

  • In the Uncert. edit box, enter the incident power uncertainty (random variation as a percentage).

  • Press the  Apply  button.

Note: If the mode of signal sampling (Waveform) is set to CW, increasing the sample count Ns (i.e., the voltage averaging number) decreases the displayed noise level as in the real measurement. This CW setting also affects the fluctuations in the Rectified and Pulsed sampling modes. For further details, see the Uncertainty Radius subsection of the DUT Page topic.

To define simulated temperature:

  • In the Temperature edit box, enter the desired value in Celsius.

  • In the Uncert. edit box, enter the temperature uncertainty (random variation in Celsius).

  • Press the  Apply  button.

Note: A temperature-related error may be triggered by these settings (normal range being typically 5 to 55 °C).

To define power-related bits of Error Byte:

In the Error Byte box, check or uncheck one of the checkboxes (Overflow or Low Signal). Only one box at a time can be checked. The errors are set independently of the actual incident power value.