73 lines
1.5 KiB
Matlab
73 lines
1.5 KiB
Matlab
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% this script evaluates the same gaussian excitation function, as openEMS does
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%
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clear
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close all
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clc
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f0 = 0e9;
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fc = 10e9;
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dT = 1e-12; % sample time-step
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sigma = 1/sqrt(8/9)/pi/fc;
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t0 = sqrt(18)/sqrt(8/9)/pi/fc;
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len = 2 * 9/(2*pi*fc) / dT; % gauss length
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for n=1:len
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t_(n) = (n-1)*dT;
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ex(n) = cos(2*pi*f0*((n-1)*dT - 9/(2*pi*fc))) .* exp(-((t_(n)-t0)/sigma)^2/2);
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end
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plot(t_/1e-9,ex)
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xlabel( 'time (ns)' );
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ylabel( 'amplitude' );
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disp( ['Amplitude at t=0: ' num2str(20*log10(abs(ex(1))/1)) ' dB'] );
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val = DFT_time2freq( t_, ex, [f0-fc f0 f0+fc] );
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disp( ['Amplitude at f=f0-fc: ' num2str(20*log10(abs(val(1))/abs(val(2)))) ' dB'] );
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disp( ['Amplitude at f=f0+fc: ' num2str(20*log10(abs(val(3))/abs(val(2)))) ' dB'] );
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% calculate frequency domain via slow DFT
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freq = linspace(f0-fc,f0+fc,1000);
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val = DFT_time2freq( t_, ex, freq );
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figure
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plot( freq/1e9, abs(val) )
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% overlay the FFT result
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[f,val_fft] = FFT_time2freq( t_, ex );
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val_fft = val_fft((f0-fc<=f) & (f<=f0+fc));
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f = f((f0-fc<=f) & (f<=f0+fc));
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hold on
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plot( f/1e9, abs(val_fft), 'r' )
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hold on
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if (f0==0)
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Fw = sigma*sqrt(2*pi)*exp(-0.5*(sigma*2*pi*f).^2);
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plot( f/1e9, 2*abs(Fw), 'g--' )
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legend('dft','fft','analytic')
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else
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legend('dft','fft')
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end
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xlim([0 max(f)/1e9])
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xlabel( 'frequency (GHz)' );
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ylabel( 'amplitude' );
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% dB
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figure
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val = val(freq>=0);
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freq = freq(freq>=0);
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plot( freq/1e9, 20*log10(abs(val)/max(abs(val))), 'r' )
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xlabel( 'frequency (GHz)' );
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ylabel( 'amplitude (dB)' );
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