A Vertical Transition between Microstrip Line and Air-Filled SIW at Ka-band

A low-loss vertical transition between microstrip line and air-filled substrate integrated waveguide (AFSIW) at Ka-band is proposed. The objective is to be able to connect active components based on microstrip technology with passive components based on AFSIW technology. The coupling between the quasi-TEM mode of the microstrip line and the TE
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mode of the AFSIW guide is carried out by a slot and a copper line placed on one layer of the substrate. To obtain reliable measurements, a back-to-back transition has been designed and fabricated. The measured results obtained show that over a frequency range of 27.5 GHz to 29.8 GHz the proposed transition has a reflection coefficient of between −10 dB and −15 dB and insertion losses between 0.78 dB and 1.45 dB.