Broadband Finline Ortho-Mode Transducer for the 750-1150 GHz Band

Details Broadband Finline Ortho-Mode Transducer for the 750-1150 GHz Band Broadband Finline Ortho-Mode Transducer for the 750-1150 GHz Band

May 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005stt..conf..513g&link_type=abstract

Sixteenth International Symposium on Space Terahertz Technology, held May 2-4, 2005 at Chalmers University of Technology. Göte

Physics

Optics

Scientific paper

We present the design and fabrication of a novel full waveguide band ortho-mode transducer (OMT) for operation from 750-1150 GHz, and scalable to frequencies as high as 5 THz. At submillimeter and THz frequencies, quasioptical techniques are generally used to implement dual polarization receiver systems. OMTs offer significantly increased simplicity, eliminating polarization diplexing optics. Since both linear polarizations use the same feedhorn and optics, alignment issues between polarizations are also eliminated. Advances in micromachining technology, semiconductor processing techniques and electromagnetic simulation now allow the design and fabrication of OMTs at frequencies where quasioptical approaches were the only viable option. While most OMTs used for radio as stronomy are derivatives of the Bøifot design, the proposed design uses a finline circuit to separate orthogonal linear polarizations. Unlike Bøifot type designs, the Robinson OMT is fully planar, allowing easy fabrication as a single split block waveguide structure with all ports in one plane. The finline circuit is also planar, and can be fabricated using photolithographic techniques on a thin dielectric substrate. This design uses micromachining technology to fabricate the waveguide splitblock by laser etching a silicon substrate that is later metallized. At lower frequencies, direct micromilling can be used to fabricate the split block directly. The finline chips are fabricated on a thin (1 μm) SOI substrate with thick (5 μm) gold finline metallization, and gold beam leads for chip grounding. This chip construction technique compatible with both direct and laser machined waveguide blocks. Both the waveguide and the finline structures can be scaled to frequencies as high as 5 THz using these fabrication techniques. Feedhorns are integrated with the structure at all three ports to allow testing with a Fourier transform spectrometer and 4He bolometer system. This technique can measure the throughput, cross-polarization and isolation of the OMT through comparison with a back to back feedhorn. Later, this OMT design could be a part of a fully integrated dual polarization mixer block, with the input horn, OMT and both mixers fabricated in a single flangeless split block. Integrated dual polarization mixers of this type can dramatically decrease the complexity of dual polarization imaging arrays as well as traditional single beam receiver systems at submillimeter and THz frequencies.

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