A compact sideband-separating (2SB) arrangement using a turnstile

Important requirements of a millimetre-wave heterodyne receiver for radio astronomy are that it can detect dual-linear polarisation and retain both upper and lower sidebands. One such arrangement, referred to as a sideband-separating (2SB) layout, uses a 90° phase shift on either the LO or signal path before mixing, and the upper and lower sidebands are separated into unique IF outputs once orthogonally re-combined. There is continuing interest to build arrays of heterodyne receivers and part of the challenge is to fit all of the receiver components within a given volume. To realise dual-linear polarisation and 2SB within receiver arrays, a new, more compact approach must be taken. Integrating a turnstile as the signal splitter reduces overall layout space and provides excellent polarisation isolation.