Prototype filter for polyphase implementation

[anmol]

I want to design a prototype filter for polyphase implementation. The polyphase uses FFT to analyze the spectrum. How should i go around the problem?

 

[Klen]

I am not sure if you are still looking for the answer or not, but if you are then program this in matlab, you should get a fairly good prototype filter:

t = 1;
N = number of coefficients you want for your filter (has to be an odd number)
M = number of channels (eg:4,8,16,etc)
h = zeros(1,N);

for i = -1:1/((N-1)/2):1              
    if and(i>=(-1/M),i<=(1/M))
        h(t) = sqrt((cos(i*M*pi)+1)/2);
    else
        h(t) = 0;
    end
    t = t+1;
end

 H = real(fftshift(ifft(ifftshift(h))));
fvtool(H);