Novel orthomode transducer for millimeter wave and terahertz frequencies. Design, fabrication and characterization of novel probe-based orthomode transducer

Abstract

There exist a vast number of orthomode transducer designs for microwave frequen cies. At sub-millimeter wave frequencies however, high accuracy requirements are set on the manufacturing techniques. This work seeks to design a novel orthomode transducer combining different manufacturing techniques resulting in low loss, wide bandwidth and a compact design. These are all important parameters for radio astronomy applications. Several design ideas from literature are considered. Room for improvement is iden tified and the novel design is developed using an electromagnetic full-wave solver. Fabrication of two demonstrator devices is done using CNC milling and micro fabrication in a clean-room environment. Lastly, the demonstrators are character ized. In summary, an orthomode transducer working between 270 − 385 GHz (36% frac tional bandwidth) was demonstrated. The produced devices work as proof of concept with insertion loss of 2 dB and return loss of 15 dB achieved for both polarizations symmetrically at room temperature. It is concluded that insertion loss of less than 1 dB and return loss of more than 20 dB are possible to achieve with further im provements of the design. The design is in theory scale-able to 1 THz and could be used instead of quasi-optical polarization diplexers. The design is also very compact.