Abstract
A transducer with a wide step from a post-wall waveguide to a hollow waveguide width is proposed which is tolerant against the aperture offset. The modes in the step width of about 1.50 wavelengths are stable for the aperture offset and the fields are not so perturbed while in the conventional stepped structure with step width of about 1.00 wavelength, the higher evanescent mode of TE30 is excessively enhanced by the aperture offset. The operation of the transducer with the wider step is robust for the fabrication errors in the millimeter wave band. It is also suggested that the anti-symmetrical TE20 mode which is excited only by non-zero offset or the misalignment of the aperture exists in both structures and can not be the dominant factor for the improvement. The transducers are designed and fabricated at 61.25GHz using PTFE substrate with glass fiber of εr=2.17. The bandwidth for the reflection lower than -15dB is almost unchanged (6.30-6.60GHz) for the offset from -0.2mm to 0.2mm, while it is degraded in the conventional stepped structure, from 7.65GHz for no offset to 3.30-5.70GHz for the same range of the offset.
