how to generate a chirp pulse and obtain its phase

Hi,

I would like to generate figure showing the a chirp pulse with the Gaussian envelope ( in the code) and to obtain its phase. I have execute the below code but it does not work. Because if it is correct, the spectrum should have the same shape as shown in the attached figure.

So does anyone have any idea on that?

This is the code I use:

c=3*10^8; %the speed of light
fs=10^-15; %femtosecond
nm=10^-9; %nanometer
Fs=2.35*10^16; % Sampling frequency = 10*50Hz
Ts=1/Fs; % Sampling interval
carrier_fre=2.35*10^15; %%(Hz)
 t=-0.8*10^-13:Ts:0.8*10^-13; % Sampling time instants [s]
 t0=0*fs; %%time
tau=40*fs; %%pulse duration
phi=exp(j*carrier_fre*t)
E_field=exp(-2*log(2)*((t-t0)/tau).^2)*phi; % The gaussian envelope
E_phase=angle(E_field);
%% Plot the spectrum
figure;
subplot(2,1,1),plot(t,E_field);
axis([-inf,inf , -inf,inf]) 
xlabel('time');ylabel('E (a.u.)');
title('spectrum without carrier frequency');
subplot(2,1,2),plot(t,E_phase);
axis([-inf,inf, -inf,inf])
xlabel('time');ylabel('phase (rad)');
title('Phase');

[Image Analyst]

From the help:

Description

example

y = chirp(t,f0,t1,f1) generates samples of a linear swept-frequency cosine signal at the time instances defined in array t. The instantaneous frequency at time 0 is f0, and the instantaneous frequency at time t1is f1.

example

y = chirp(t,f0,t1,f1,method) specifies an alternative sweep method option.

y = chirp(t,f0,t1,f1,method,phi) specifies the initial phase.

example

y = chirp(t,f0,t1,f1,'quadratic',phi,shape) specifies the shape of the spectrogram of a quadratic swept-frequency signal.

[dang khoa tran]

In fact, I also try this f0=2.35E15 at t but how to identify the f1 at t1 if it is a up-chirp? And how to obtain the phase of this chirp?

Could you please help me to clarify?

Answer 1

[Priyanshu Mishra]

Hi Dang,

To generate a chirp pulse, you may refer to following link.