Fractional Delay using Polyphase Filter How to use rectangular window design to design a length-9 polyphase filter which delays an input signal by 3/5 of a sample? An expression for the 9 coefficients is required.
Just sample a Sinc function at the appropriate phase offset, and truncate the FIR as needed to meet your rectangular window length requirement.  You only need 1 phase for a constant delay while keeping the same sample rate.