Revisiting the performance of free-standing polarizing wire grids in light of the use of cross grids

Le résumé fourni par la source

Free-space polarizing wire grids are often a vital component in quasi-optical circuits. We have long held the belief that they are close to perfect components. An example of this is their ability to create circular polarization (CP) based circulators with extremely good performance (isolation > 50dB) enabling, for example, the W-band cloud profiling radar multiplexing on EarthCARE [1].We are using polarizing wire grids in a number of future space-based projects, for example WIVERN – a candidate for ESA’s 11thEarth Explorer mission - is a dual-polarization W-band doppler radar that uses wire grids to combine and separate channels in a novel cross-grid geometry, presented here.However experimental results from a WIVERN breadboard have led us to challenge the assumption that free-standing polarizing wire grids are perfect components. We have seen higher levels of cross-polar generation where a component of the electric field of a gaussian beam on boresight (Ez) – necessary for Div.E to be zero - is allowed to interact with the long axis of the wires. We have matched experimental result and model, and refined our knowledge of how to apply free-standing polarizing grids in low-gain beams, where this effect is most pronounced.

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