RRI Receiver PFB Filter

The RRI receivers use a 512 channel, 8 tap, Polyphase Filter Bank. The (signed 12 bit) coefficients of this filter are contained in the following file: 

The Coefficients:

Frequency Response:

Computing the expected bandpass response (including aliasing and leakage effects):

The actual power observed in the MWA coarse channels are affected by aliasing and leakage due to the fine channeliser. The following script can be used to generate the bandpass response at any valid MWAX frequency resolution:

usage:

python3 compute_pfb_aliased_bandpass_MWAX.py <fine-channel resolution in kHz>

First, the script computes the frequency response at the 200Hz ultra-fine channel resolution.

Next it computes the aliased components by shifting the frequency response +- 1 coarse channel across and summing the total power as shown in the following diagram:

Finally, the script combines ultra-fine channels together to form wider fine-channels, as done in the MWAX correlator.

The result is the following expected bandpass response (for 10kHz fine channels):