I want to design FD (frequency dependent ) IQ (In-phase,Quadrature) distortion that changes the phase mismatch linearly like a+b*K ( where K is the subcarriers 1 to 64) and amplitude remains constant to test my estimation algorithm against it. I need this filter to be in time domain before FFT but changes the IQ imbalance parameters across different subcarriers(hence the name FD) .I wonder how to achieve this ? I was thinking something like H = alpha *exp(2*pi*1i*(a+b*K)) as the frequency response and just take the IFFT of this and convolve with the signal. Do you think this is correct , any help will be appreciated ?