Digital channelizer with arbitrary output sampling frequency

DETAILED DESCRIPTION OF THE EMBODIMENTS Referring to FIG.
5, a polyphase channelizer 200 according to an embodiment of the invention employs a shift register 210 to distribute the time series data over input channels 220 to an FFT block 230 instead of the commutator 141 of the device of FIG.
2.
Referring now also to FIGS.
3 and 4, the contents of filter registers denoted h.
sub.
i (m) and corresponding data registers corresponding to the polyphase system of FIG.
5 are represented as a chart with the condition of the registers at a certain point in time and the condition of the registers after 2N additional points have been sampled.
In a conventional poly-phase application, the data registers would be shifted by exactly the size of the following FFT, that is, by the number of input channels.
Thus, if the FFT has 2N inputs, the 2N data points would be distributed by the shift register and the FFT invoked.
FIG.
3 shows the contents of an example in which the FFT is of size 2N=14 and FIG.
4 shows the contents 2N=14 samples later (equivalent to one sweep of the commutator 141).
Referring to FIG.
6, the spectrum of an example data set with 4 or 6 frequency bands that need to be separated digitally is shown.
The dashed lines show the ideal spectral response of analog band pass filtering typically employed to filter the analog signal prior to digitizing.
The short-long dashed line shows the spectral response of a less ideal BPF with a slower cutoff rate.
Referring again to FIG.
5, a series of polyphase filters h.
sub.
i (m) are employed.
Each filter is formed by taking every 1/2N.
sup.
th point of a low pass filter finite-impulse-response (FIR) that would ordinarily be needed to extract one band of width B from the input data sample at 2NB.
If a P tap FIR is required to meet the channel separation specification, then each of the polyphase filters h.
sub.
i (m) consists of P/2N taps.
Shift register buffer 210 distributes the input data to the 2N digital filters h.
sub.
i (m), one for each input to FFT module