Wideband 220–330GHz Turnstile OMT Enabled by Silicon Micromachining

This paper is the first publication on the first turnstile-junction orthogonal mode transducer (OMT) above 110GHz, which is enabled by silicon micromachining. In contrast to other OMT concepts, turnstile OMTs are wideband and allow for co-planar ports, but require accurate and complex fabrication and have therefore, to the best of our knowledge, not been implemented above 110GHz in any technology. As shown in this paper, the fabrication and assembly accuracy of silicon micromachining enables the realization of such complex OMT designs at 220–330GHz with excellent performance. The measured insertion loss is better than 0.7dB for the whole waveguide band, with mean values of 0.34dB and 0.48dB for the vertical and horizontal polarizations, respectively. The measured return loss for both polarizations, even with an open-ended common port, is better than 14dB for the whole waveguide band, and an average level of 18dB. An estimation of the worst-case cross-polarization level, derived from measurements, results in at least 20dB for the whole waveguide band, with an average of 25dB for the upper half of the band.