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This work presents a 16-way Ku-band radial power combiner for high power and high frequency applications, using the very low loss TE circular waveguide mode. The accomplished design shows an excellent performance: the experimental prototype has a return loss better than 30 dB, with a balance for the amplitudes of (±0.15 dB) and (±2.5°) for the phases, in a 16.7% fractional bandwidth (2 GHz centered at 12 GHz). For obtaining these outstanding specifications, required, for instance, in high-frequency amplification or on plasma systems, a rigorous step-by-step procedure is presented. First, a high-purity mode transducer has been designed, from the TE mode in the rectangular waveguide to the TE mode in the circular waveguide, with very high attenuation (>50 dB) for the other propagating and evanescent modes in the circular waveguide. This transducer has been manufactured and measured in a back-to-back configuration, validating the design process. Second, an E-plane 16-way radial power divider has been designed, where the power is coupled from the 16 non-reduced-height radial standard waveguides into the TE circular waveguide mode, improving the insertion loss response and removing the usual tapered transformers of previous designs limiting the power handling. Finally, both the transducer and the divider have been assembled to make the final radial combiner. The prototype has been carefully manufactured, showing very good agreement between the measurements and the full-wave simulations.

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This chapter presents a comprehensive analysis of the applications of a low-cost version of additive manufacturing (AM). The technique called Fused Filament Fabrication (FFF), which makes use of plastic as raw material, is explained in the context of its applications to the microwave waveguide engineering field. The main advantages of this technology include the promptness to print models, the variety of feasible geometries, and specially the reduced cost. The main limitations are also explained. Two important applications are considered: (1) rapid prototyping of complex devices and (2) manufacturing of fully functional devices. The former is relevant to get a more realistic perspective of the actual geometry in computer-aided designs, as shown in several examples. It also helps to forecast possible issues in the fabrication process that the computer sometimes fails to detect at the design stage. In the latter case (2), the subsequent and necessary metallization of plastic devices is also addressed. Several examples of state-of-the-art passive waveguide devices are presented, including waveguide filters, a diplexer, a branch-line coupler, a load or horn antennas, which have been printed, metallized, and measured. The results show the potential of three-dimensional (3D) printing and provide a different insight into this innovative technology.