A 90$^\textrm\textbackslashcirc\$$ curved microstrip transmission line is characterized in the time domain and frequency domain with the transmission line matrix method in 3D space and with supporting measurements up to 40 GHz. Results of this structure realized on 10 mm alumina substrate are presented. The S-parameters as a function of frequency and the time-domain step response are discussed in detail. The microstrip line consists of a bend with short straight transmission lines on both sides of the bend. The structure is placed in a 90$^\textrm\textbackslashcirc\$$ corner with two electric walls, which represent a housing. The other two sides and the top lid are far removed in order to avoid any additional disturbances of the fields. Measurements and simulation verify the operation at frequencies above 40 GHz
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