Designing artificial signals I'm trying to design a sample signal that has two "components". I want the signal to look like the upper left figure, with the two components shown on the right. The time frequency spectrum is shown in the bottom left. 



I'm using MATLAB to generate this signal, as I am running MATLAB code that uses these signals. I have been trying my heart out with a combination of chirps, sincs and cos functions, but I just can't for the life of me reproduce this sort of a spectrogram. What I have produced looks like this:



It's quite close I feel, but there is something missing. Can someone point me to a way to approach this?

EDIT: 

This is the code I use:

fs = 5000;
x0 = 1;
t = -x0:1/fs:x0;
yi = cos(t).*sinc(t).*chirp(t,150,0.2,250,'quadratic'); 
yj = cos(t).*sinc(t).*chirp(t,50,0.4,150,'quadratic'); 
subplot(2,2,1)
plot(t,yi+yj)
subplot(2,2,2)
plot(t,yj)
subplot(2,2,3)
spectrogram(yi+yj,512,511,256,fs,'yaxis')
subplot(2,2,4)
plot(t,yi)
In the code below I have manually created chirps where the frequency does not increase linearly, but behaves in a cosine-shape, as suggested by Atul Ingle . This waveform resembles the shape of the lines in the spectrogram nicely.

fs = 5000;
x0 = 1;
t = -x0:1/fs:x0;
yi = cos(t).*sinc(t/1.5).*cos(2*pi*500*(1.8-cos(2.2*t)).*t); 
yj = cos(t).*sinc(t/1.5).*cos(2*pi*500*(0.85-0.5*cos(2.3*t)).*t); 
subplot(2,2,1)
plot(t,yi+yj)
subplot(2,2,2)
plot(t,yj)
subplot(2,2,3)
spectrogram(yi+yj,512,511,256,fs,'yaxis')
subplot(2,2,4)
plot(t,yi)