A compact ultra-wideband ridge waveguide to coaxial line transition

A novel compact single-ridge waveguide (SRW) to coaxial line ultra-wideband transition is proposed in this paper. The transition using shorter matching networks between the coaxial port and the SRW port achieves maximum matching bandwidth; meanwhile, a wideband short circuit is also introduced to further broaden bandwidth performance. The whole structure is very simple and can be readily fabricated with a conventional computer numerical control machine. The prototype transitions were designed, manufactured, and measured. The measured results are reasonably consistent with the simulated results. Measurements show that the return loss and insertion loss of the back-to-back transition are better than 18 dB and 0.2 dB, respectively, from 6 to 18 GHz, with 100% fractional bandwidth. Besides, the measured return loss of the single transition is higher than 23 dB in the entire bandwidth. Compared with some other reported SRW transitions, the proposed SRW transition exhibits extreme compactness, lower insertion loss, and more excellent bandwidth performance. The dimensions of the transition structure are only 0.75λ * 0.7λ * 0.35λ (λ is the wavelength at the center frequency) for the central frequency of 12 GHz. The design's transition is completely scalable to other needed frequency band.