thank u for ur response
i finally did it with the help of Fm modulation...i think LFm will do also fine
here is what i have done have
T=2e-6;
Fs=440e6;
Fc=120e6;
B=200e6;
ft=0:1/Fs:T-1/Fs;
N=length(ft);
k=(Fc/Fs)*2*pi/max(ft);
y=modulate(ft,Fc,Fs,'fm',k); %%band pass
y_fft=fft
;
y1=y_fft %(1:N/2);
figure;
subplot(2,1,1);
plot(ft,y);
xlabel('t');
ylabel('y');
title('modulated output signal(t)');
subplot(2,1,2);
plot((0:Fs/N:Fs-Fs/N),abs(y_fft));
xlabel('frequency(Hz)');
title('frequency respone');
axis([-50e07 50e+07 0 50])
x=ifft(y1); %%bandpass final
figure
plot(ft,x)
j=sqrt(-1);
x1=x'*exp(-j*2*pi*120e6*ft); %% lowpass
figure
plot((-(Fs-Fs/N)/2:Fs/N
Fs-Fs/N)/2),abs(fft(x1)))