A polarimetric radiometer that operates at a frequency of 40 GHz has been designed and built as a prototype of multiple identical units that could be arranged in a planar array for scientific measurements. Such an array is planned for use in studying the cosmic microwave background (CMB).

All of the subsystems and components of this polarimetric radiometer are integrated into a single multi-chip module (MCM) of substantially planar geometry. In comparison with traditional designs of polarimetric radiometers, the MCM design is expected to greatly reduce the cost per unit in an array of many such units.

The MCM performs all the microwave functions (other than initial reception and orthomode transduction) of a polarimetric microwave radiometer.
The design of the unit is dictated partly by a requirement, in the planned CMB application, to measure the Stokes parameters I, Q, and U of the CMB radiation with high sensitivity. (A complete definition of the Stokes parameters would exceed the scope of this article. In necessarily oversimplified terms, I is a measure of total intensity of radiation, while Q and U are measures of the relationships between the horizontally and vertically polarized components of radiation.) Because the sensitivity of a single polarimeter cannot be increased significantly, the only way to satisfy the high-sensitivity requirement is to make a large array of polarimeters that operate in parallel.

The MCM includes contact pins that can be plugged into receptacles on a standard printed-circuit board (PCB). All of the required microwave functionality is implemented within the MCM; any required supporting non-microwave (“back-end”) electronic functionality, including the provision of DC bias and control signals, can be implemented by standard PCB techniques.

On the way from a microwave antenna to the MCM, the incoming microwave signal passes through an orthomode transducer (OMT), which splits the radiation into an h + i? beam and an h – i? beam (where, using complex-number notation, h denotes the horizontal component, ? denotes the vertical component, and ±i denotes a ±90° phase shift). Each of these beams enters the MCM through one of two WR-22 waveguide input terminals in the lid of the MCM. The h + i? and h – i? signals are amplified, then fed to a phasediscriminator hybrid designed specifically to fit the predominantly planar character of the MCM geometry and to enable determination of Q and U. The phase-discriminator hybrid generates four outputs, which are detected and used to calculate I, Q, and U.

This work was done by Pekka Kangaslahti, Douglas Dawson, and Todd Gaier of Caltech for NASA’s Jet Propulsion Laboratory. NPO-41335.

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MCM Polarimetric Radiometers for Planar Arrays

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NASA Tech Briefs Magazine

This article first appeared in the September, 2007 issue of NASA Tech Briefs Magazine (Vol. 31 No. 9).

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Overview

The document outlines a technical disclosure related to the development of MCM (Multichip Module) Polarimetric Radiometers for Planar Arrays, identified by NTR Number 41335, and dated September 23, 2004. The primary motivation behind this innovation is the need to detect the Q and U Stokes polarization parameters of cosmic background radiation with high sensitivity. Traditional polarimeters have limitations in sensitivity improvements, necessitating the creation of large arrays of polarimeters that can operate in parallel. However, to make this approach feasible, it is crucial to significantly reduce the cost per polarimeter compared to conventional designs.

The solution presented involves the integration of the complete Q/U detecting polarimeter into a single multichip module (MCM). This MCM is designed as a planar module with pins that can easily connect to a standard printed circuit board (PCB). By consolidating all microwave functionality within the MCM, the backend electronics can be constructed using standard PCB technology, streamlining the manufacturing process and reducing costs.

The novelty of this work lies in the development of a planar radiometer capable of detecting electromagnetic radiation polarization, which is a significant advancement over prior art. The integration of the polarimeter into a single MCM not only enhances the efficiency of the detection process but also allows for the construction of large arrays at a lower cost, making high-sensitivity measurements more accessible.

The document is part of NASA's Commercial Technology Program, which aims to disseminate aerospace-related developments that have broader technological, scientific, or commercial applications. It emphasizes the potential for further assistance and collaboration through NASA's Innovative Partnerships Program.

In summary, the document presents a significant technological advancement in the field of polarimetry, specifically for applications related to cosmic background radiation. By integrating polarimeters into cost-effective multichip modules, this innovation paves the way for enhanced sensitivity in measurements and opens up new possibilities for research and exploration in astrophysics and related fields. The work is supported by NASA's Jet Propulsion Laboratory, highlighting its importance and potential impact on future scientific endeavors.