GTD-PO 6.2.10

12.5. Doppler

This option will be availabe when the simulation type selected in the Simulation Parameters window is Doppler.

12.5.1. Doppler Spectrum

This option allows the user to see a 2D graph of the field values for each frequency of the Doppler frequency Spectrum Shift. The frequency scale is relative to the carrier frequency, that means that a 0.0 frequency shift is for a signal that does not suffer any frequency shift (it frequency is exactly the carrier frequency).

 

To plot a graph, the user can select the field component, the polarization, the step, the carrier frequency and the Doppler Period (). A new graph will be plotted with the button 'Add Series'. In the case that the user has set up a parametrized geometry (see the GUI User Guide for details), it is possible to select the step to visualize the results for.

It is also possible to delete a serie that is selected by the user from the list with the 'Remove Series'. The display option also allows changing the color of the series and display points. The buttons 'Import Series' and 'Export Series' are used for importing and exporting the selected series in 'List of Series' to a data file written as a text file.

This panel displays a plot with the results, and several options for adding and removing extra series from the plot.

When initially open, the panel will display a default series in the plot that will represent the measurements for a particular component, polarization and step. More series can be added, by selecting component, polarization and step that appears leftside to the plot.

  • Component: select the cartedian component of the field to visualize the results. The enabled options are Ex, Ey, Ez and ETotal.
  • Polarization: select thepolarization component of the wave to visualize the results. Select one of the possible values: Vertical, Horizontal. If the source has been defined as a radiation pattern, this combo box will not be available.
  • Step: select the simulation scene to visualize the results. These should have been defined prior to the calculation when designing the simulation.
  • Frequency: select the simulation frequency (as the carrier frequency) to visualize the results.
  • Period: select the simulation doppler period (Only will be enabled if Doppler FMCW option is selected on Doppler parameters) to visualize the results.

 

Doppler Spectrum panel

 

12.5.2. Text Files

This option shows the same file as section 12.3.2. View Text Files on Ray Tracing results. First, a panel should appear after selecting this menu option to wait for step and period parameters to open the desired file.

File Selection panel

 

To use this section, select a parametric step from the list and a Doppler period (only will be enabled if Doppler FMCW option is selected on Doppler parameters) to get the results from and click on OK to load the data of the present rays.

 

Ray File Panel

To generate a copy of the file click on ‘Save as…’ button and select the file path to save the copy.

 

12.5.3. FMCW

When the user selects a simulation of type Doppler and defines the Doppler parameters including FMCW, this option will be visible on the ‘Show Results --> Doppler’ option of the menu bar.

This option allows the user to visualize the spectrum of the field for one time or more times in the signal periods. Then, selecting a determinate instant of time, the user can see the Doppler Spectrum. The user can select one or more instants of time over all the periods simulated.

FMCW Parameters

  • Period: indicates, on seconds, the period duration on time. This parameters is configured on section 6.3 Doppler.
  • Number of periods: indicates the number of repeats for the frequency variation. This parameters is configured on section 6.3 Doppler.
  • Step: select the parametric scene to realize the analysis.
  • Frequency: select the carrier frequency for the analysis. This frequency will be one of the simulation frequencies.
  • Initial Frequency: indicates, on GHz, the frequency selected to be the carrier frequency.
  • Function of 'x': assign the user function frequency signal.
  • Distance Range: indicates, on meters, the maximum distance considered in the simulation that rays can travel from transmitter to receptor including rebounds with obstacles.
  • t(s): allows to add instant of time to analyze. Selecting an instant of time, in seconds, and clicking on the ‘Add’ button (green icon with the plus sign) the instant will be added to the analyzing list. Selecting a row from the list and clicking on the ‘Delete’ button (red ‘X’ icon) the selected instant will be removed from the analyzing list.

The frequency signal can be defined by a user function, where the x coordinate is the time in seconds. These functions are defined without parameters and return a double data type. These functions can use the $x variable, which is assigned the value of time in seconds and $period variable that equals the period value. The $x variable is always less or equal than $period.

The application includes by default five user functions for usage in FMCW. They are in the functions directory.

Sawtooth wave (fmcw_1.java):

double fmcw_1(){
    // This function returns the frequency increment from time '$x'
    // Global parameters
    // $period: period time in seconds.
    // $x: time within the period.
    // 
    // Note: '$x' it is always less than '$period'
    //
    double MAX_BROADBAND = 0.3; // GHz
    return ($x * MAX_BROADBAND) / $period;
}

FMCW User function sawtooth wave

Square wave (fmcw_2.java):

double fmcw_2(){
    // This function returns the frequency increment from time '$x'
    // Global parameters
    // $period: period time in seconds.
    // $x: time within the period.
    // 
    // Note: '$x' it is always less than '$period'
    //
    double x1 = 1./3 * $period;
    double x2 = 2./3 * $period;
    
    if($x < x1) {
        return 0.0;
    } else if($x < x2) {
        return 0.1;
    } else {
        return 0.2;
    }
}

FMCW User function square wave

Range wave (fmcw_3.java):

double fmcw_3(){
    // This function returns the frequency increment from time '$x'
    // Global parameters
    // $period: period time in seconds.
    // $x: time within the period.
    // 
    // Note: '$x' it is always less than '$period'
    //
    double x1 = 1./3 * $period;
    double x2 = 2./3 * $period;
    double x3 = $period;

    double y1 = 0.1;
    double y2 = 0.2;

    if($x < x1) {
        return y1/x1 * $x;
    } else if($x < x2) {
        return y1;
    } else {
        return y1 + ((y2-y1)/(x3-x2)) * ($x-x2);
    }
}

FMCW User function range wave

Triangular wave (fmcw_4.java):

double fmcw_4(){
    // This function returns the frequency increment from time '$x'
    // Global parameters
    // $period: period time in seconds.
    // $x: time within the period.
    // 
    // Note: '$x' it is always less than '$period'
    //
    double BROADBAND = 0.3;
    // first point
    double x0 = 0;
    double y0 = 0;
    // second point
    double x1 = 1./2 * $period;
    double y1 = BROADBAND;
    // third point
    double x2 = $period;
    double y2 = 0;

    if($x < x1) {
        double pending = (y1-y0)/(x1-x0);
        double xOffset = x0;
        double yOffset = y0;
        return pending * ($x-xOffset) + yOffset;
    } else {
        double pending = (y2-y1)/(x2-x1);
        double xOffset = x1;
        double yOffset = y1;
        return pending * ($x-xOffset) + yOffset;
    }
}

FMCW User function triangular wave

Sinusoidal wave (fmcw_5.java):

double fmcw_5(){
    // This function returns the frequency increment from time '$x'
    // Global parameters
    // $period: period time in seconds.
    // $x: time within the period.
    // 
    // Note: '$x' it is always less than '$period'
    //
    double BROADBAND_GHZ = 3.0e-3;
    // change [0, $period] range to [0, 2*PI] range    
    double radians = ($x * (Math.PI*2)) / $period;
    return Math.sin(radians) * BROADBAND_GHZ;
}

FMCW User function sinusoidal wave

See further information in GUI User Guide.

When all the previous parameters will be defined, clicking on "View FMCW Spectrum" button, the spectrum chart appears.

FMCW Spectrum, Data Values

To save the data table values click on the ‘Save as...’ button and select the path for the file.

This chart indicates, for each frequency on the broadband, the contribution of the rays emitted in the frequency and came to the receptor at time ‘t’. The frequency values on X-axis will be indicated referenced to the current frequency (‘Ft’) on the analyzing instant, then a contribution of -2000 Hz means a contribution of a rays emitted to 2000 Hz below of the current frequency.

FMCW Spectrum, Chart

  • t: Indicates the instant of time that ‘Time’ parameter referenced.
  • Ft: indicates the current frequency. This frequency is the frequency on the instant of time ‘t’.
  • Bin: divides the spectrum and modifies the beat signal frequency domain and the beat signal time domain charts.

FMCW Spectrum, Beat signal frequency domain

FMCW Spectrum, Beat signal time domain

We use cookies on this website to improve your navigation experience on this site. By using this site, you agree to our cookie policy.

I agree