In this activity, we develop novel focal plane detector pixels for the next generation CMB B mode detection missions. Such future mission designs will require focal plane pixel technologies that optimizes the coupling from telescope optics to the large number of detectors required to reach the sensitivities required to measure the faint CMB polarization traces. As part of an ESA Technical Research Programme (TRP) programme we are tasked with developing, manufacturing and experimentally verifying a prototype multichroic pixel which would be suitable for the large focal plane arrays to reduce the focal plane size requirement. The concept of replacing traditional single channel pixels with multi frequency pixels will be a key driver in future mission design and the ability to couple radiation effectively over larger bandwidths (30 - 100%) is a real technical challenge. In the initial part of the programme we reviewed the science drivers and this determined the technical specifications of the mission. Various options for focal plane architectures were considered and then after a tradeoff study and review of resources available, a pixel demonstrator was selected for design manufacture and test. The chosen design consists of a novel planar mesh lens coupling to various planar antenna configurations with Resonant Cold Electron Bolometer (RCEB) for filtering and detection of the dual frequency signal. The final cryogenic tests are currently underway and a final performance will be verified for this pixel geometry.
The main objective of this activity is to develop new focal plane coupling array concepts and technologies that
optimise the coupling from reflector optics to the large number of detectors for next generation sub millimetre
wave telescopes particularly targeting measurement of the polarization of the cosmic microwave background
(CMB). In this 18 month TRP programme the consortium are tasked with developing, manufacturing and
experimentally verifying a prototype multichroic pixel which would be suitable for the large focal plane arrays
which will be demanded to reach the required sensitivity of future CMB polarization missions. One major
development was to have multichroic operation to potentially reduce the required focal plane size of a CMB
mission. After research in the optimum telescope design and definition of requirements based on a stringent
science case review, a number of compact focal plane architecture concepts were investigated before a pixel
demonstrator consisting of a planar mesh lens feeding a backend Resonant Cold Electron Bolometer RCEB for
filtering and detection of the dual frequency signal was planned for manufacture and test. In this demonstrator
the frequencies of the channels was chosen to be 75 and 105 GHz in the w band close to the peak CMB signal.
In the next year the prototype breadboards will be developed to test the beams produced by the manufactured
flat lenses fed by a variety of antenna configurations and the spectral response of the RCEBs will also be
verified.
Current and future generations of astronomical instruments in the millimetre (mm) and sub-mm range are in
need of increased sensitivity through the use of ever larger focal planes with 1000s of pixels. Mass, dimensions
and manufacture requirements, mainly for new space missions, is driving the technology to go from feedhorn,
and generally waveguide based cold optics to planar coupled detectors, while maintaining RF performance. The
present results of a current ESA TRP are presented with respect to the work on planar antennae that will be
coupled to cold bolometric detectors through the use of planar mesh lenses. Two planar antennae operating at
W-band are developed, namely, a broadband sinuous antenna and a variation on the classical dual-slot antenna
to realise multi-band functionality.
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