function chirpwavedown=waveform(fc,tm,B)
fc=50e9;
tm=5e-9;
smp=fc*tm;
t=linspace(-tm/2,tm/2,smp);
B=5e8;
mu=-B/tm;
chirpwavedown=cos(2*pi*4e8*t+pi*mu*(t.^2));
plot(t,chirpwavedown);