12.5. Doppler
This option will be availabe when the simulation type selected in the Simulation Parameters window is Doppler.
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This option will be availabe when the simulation type selected in the Simulation Parameters window is Doppler.
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.
Doppler Spectrum panel
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.
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
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
FMCW Spectrum, Beat signal frequency domain
FMCW Spectrum, Beat signal time domain