The C-BASS receivers are a hybrid of a correlation radiometer and a correlation polarimeter. This receiver architecture was chosen to provide stable measurements of both total intensity (Stokes I) and linear polarisation (Stokes Q and U). C-BASS North covers the 4.5 to 5.5 GHz band in a single analog channel with a custom digital readout, while the C-BASS South receiver implements the same architecture with a digital back-end that also provides spectral resolution within the band.
Schematics of the C-BASS receivers are shown below.
Some of the features of the receiver which are intended to reduce systematics are:
- Temperature-stabilised loads are used to obtain accurate total power measurements.
- Each circular polarisation is spread over two amplifier chains to lessen the effects of gain drift (a balanced receiver).
- All the signal paths are phase switched with orthogonal Walsh functions.
We have designed all of the components in the receiver with low cross-polarisation as our primary consideration. One of the major technical hurdles we have overcome was designing a broadband, compact, low cross-polarisation Orthomode Transducer (OMT).