Wideband In-Line Waveguide-to-Microstrip Transition With Antisymmetric Rectangular Probes

In this letter, a simple and clear in-line waveguide-to-microstrip (MS) transition using a pair of antisymmetric rectangular probes is presented for monolithic millimeter-wave integrated circuit (MMIC) packaging. The two rectangular probes are arranged on both sides of a substrate within the <tex-math notation="LaTeX">E</tex-math> -plane waveguide. The probe tips are close to two sides of the waveguide and their roots overlap, which help them gradually rotate the coupled <tex-math notation="LaTeX">E</tex-math> -field from the waveguide into the microstrip. The probe tip is one-quarter wavelength away from the back-short for the maximum <tex-math notation="LaTeX">E</tex-math> -field coupling. Moreover, quarter-wavelength lines are used to match the probe to the 50- <tex-math notation="LaTeX">Ω</tex-math> line in a wideband. To verify the package effect, the MMIC was replaced by a 50- <tex-math notation="LaTeX">Ω</tex-math> microstrip, and a passive back-to-back prototype was demonstrated. In the entire <tex-math notation="LaTeX">W</tex-math> -band (75–110 GHz), the back-to-back package achieves a return loss of higher than 13 dB with an average insertion loss of 1.29 dB.