Compact in-line waveguide-to-microstrip coaxial probe transition for millimeter-wave

A novel in-line waveguide-to-microstrip transition using coaxial probe structure in the U-band is proposed. This transition has the advantages of low loss, compact structure and hermetic package. A metal post is inserted into the center E-plane of the waveguide to prompt the conversion of electromagnetic wave. Experimental results of the transition verify the validity of the design. A net transition loss of 1 dB is obtained within a wide frequency range from 42 GHz to 50 GHz. The length of overall transition is less than 0.7 ¿g, which is wavelength of the operation center frequency.