Focal Plane Array Concept for ALMA 2030

Focal plane arrays (FPA), integrated into total power antennas, are noted as a desired technology for ALMA development during the 2030s.  For full compatibility with ALMA, a dual-linear, sideband-separating (2SB) architecture is necessary.

We report on a conceptual design that uses a “unit cell” approach for the front-end 2SB block using waveguide.  Each pixel uses a turnstile OMT for linear polarization, hybrid-tees for isolated power division and higher mode termination, and hole couplers for LO injection.  A 5-layer quasi-platelet layout is used such that the “unit cell” is replicated to facilitate arrayed designs.  Mixers are separately housed within a simplified DSB mixer block (using standard split-block) that allows for separate mixer qualification.

In collaboration with ASU, a waveguide hybrid-tee, scaled for ALMA Band 6, is currently under development to explore the machinability and performance of the component itself, and the notion of using platelet designs at Band 6 frequencies.