Improvements in bandwidth and frequency capability of microwave power combinatorial techniques

THE DEVELOPMENT of a technique for combining successfully the power from a number of X-band IMPATT coaxial circuit modules has been previously discussed’. Briefly, the coaxial modules (developed from a circuit described earlier’) are transmission lines which are series loaded (magnetically coupled) at some point along their length to a high Q, TICIono resonant cylindrical cavity. As shown in Figure 1, the coaxial modules have a quarter-wave transformer at the IMPATT end (to transform the low IMPATT impedance) and are terminated in a material that is amicrowave absorber and a dc insulator. The coaxial modules are located around the circular periphery of the cylindrical cavity. Figure 2 is a photograph of a typical 16-diode power combiner designed along these lines. The combiner uses a Titlolo mode aluminum cavity and has a computed Qo of 6500. In amplifier operation this combiner has an output power of 20 W at 3-dB gain. Its bandwidth is 125 MHz; a gain curve for several input powers is shown in Figure 3