Wideband Transition From Microstrip Line-to- Empty Substrate-Integrated Waveguide Without Sharp Dielectric Taper

In this letter, a wideband transition from microstrip line-to-empty substrate-integrated waveguide (ESIW) without sharp dielectric taper is proposed. A section of ESIW with an expanded width is employed to replace the commonly used dielectric taper. The dielectric loss of the taper is eliminated, and the low reflection is achieved over a broad bandwidth. A design procedure is presented to provide initial dimensions of the transitions for different frequency bands and different substrates. A tolerance analysis shows that the reflection performance is insensitive to the dimensional parameters related to the printed circuit board cutting process. A Ku-band back-to-back transition prototype has been designed and manufactured using RO4350B substrate of 0.508-mm thickness to validate its performance. The measured return loss is better than 21 dB with an insertion loss of 0.83 ± 0.25 dB (0.415 ± 0.125 dB for a single transition) over the entire Ku-band.