Optimum stepped transformers from rectangular waveguide to ridged and all-metal finned waveguides are designed with the method of field expansion into eigenmodes, which includes higher order mode interaction between the step discontinuities. Computer-optimized design data are given for a Ku-band ridged waveguide prototype with a ridge width of 1 mm, as well as for Ku-band and E-band finned waveguide transformers with commercially available metal fin thicknesses of 0.19 mm and 0.1 mm, respectively, suitable for metal-etching manufacturing technique. The optimum designs achieve a minimum return loss of about 36 dB, or 34 dB for the whole Ku- or E-band, respectively. The theory is verified by comparison with measured results.

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Modal-S-Matrix Design of Optimum Stepped Ridged and Finned Waveguide Transformers

Most reported spatially combined or quasioptical amplifier arrays exhibit resonant narrowband performance (<10%) and have not addressed thermal management issues. We report a waveguide-based spatial combining scheme using broadband tapered-slot transitions, capable of realizing full waveguide band coverage (40% fractional bandwidth) with good thermal properties. An X-band prototype using eight medium-power GaAs monolithic microwave integrated circuits (MMICs) produced an output power of 2.4 W and 9-dB power gain at 1-dB compression, with a combining efficiency of 68% and </spl plusmn/1-dB gain variation over the full waveguide band (8-12 GHz).

Broadband spatially combined amplifier array using tapered slot transitions in waveguide

Dense arrays of tapered-slot or finline transitions have proven useful in the design of compact spatial power combiners. In this paper, a design procedure is established for tapered finline arrays, providing a broad-band impedance match to a target load over the waveguide band. The procedure is based on an extension of the Klopfenstein optimal taper design to non-TEM waveguiding structures, and employs the spectral-domain method for the computation of propagation constants in the array structure. The method has been experimentally verified for a small X-band array. Data are also presented, which show that insertion loss in the finline arrays is independent of the number of array elements, assuming the designs are optimized for the desired return-loss characteristics in each case.

Design of waveguide finline arrays for spatial power combining

Both 1.6- and 3.3-W power-amplifier (PA) modules were developed at 24 GHz using a waveguide-based power combiner. The combiner is based on a double antipodal finline-to-microstrip transition structure, which also serves as a two-way power combiner. The proposed 1/spl times/2 combining structure was analyzed and optimized by finite-element-method (FEM)-simulations and experiments. An optimized 1/spl times/2 power combiner showed a very low back-to-back insertion loss of 0.6 dB and return losses better than 17 dB over most of Ka-band. The resonant behavior of the combiner was also identified and analyzed using an FEM simulator. The two-way power-combining approach was extended to four-way (2/spl times/2) power combining by vertical stacking inside the waveguide. No degradation in the combining efficiency was observed during this process, demonstrating the scalability of the proposed approach. The implemented 1/spl times/2 power module that combines two 1-W monolithic-microwave integrated-circuit (MMIC) PAs showed an output power of 1.6 W and a combining efficiency of 83% around 24 GHz. The 2/spl times/2 PA module combining the four 1-W MMICs showed an output power of 3.3 W together with an almost identical combining efficiency. This paper demonstrates the potential of the proposed power combiner for high-power amplification at millimeter-wave frequencies.

1.6- and 3.3-W power-amplifier modules at 24 GHz using waveguide-based power-combining structures

In this paper, a novel transition, based on the ridged-waveguide together with the microstrip-probe approach, is proposed. With this structure, it overcomes the difficulties in the mounting reproducibility and DC-block restriction of the ridged-waveguide-to-microstrip transition in applications. Centered at 42.5GHz, such a transition, employing Duriod based substrates, has been designed and verified by the HFSS simulator. Also, the simulation results are presented.

A Novel Waveguide-to-Microstrip Transition for Millimeter-Wave Applications

This paper presents closed-form expressions for the design of a quarter-wave transition-matching transformer. This structure takes the form of a notch or protrusion cut in the finline substrate at the waveguide-to-finline interface. The dimensions of the transformer are calculated using a homogeneous waveguide model for the partially loaded sections. The characteristics of this model are found with perturbation theory. Several transformers were designed and measured. A 5-dB improvement in return loss over a full waveguide band is typical.

W.J.R. Hoefer

Papers

Quarter-Wave Matching of Waveguide-to-Finline Transitions (Short Papers)