$Ka$ -Band Symmetric V-Shaped Meander-Line Slow Wave Structure

A symmetric configuration of two V-shaped microstrip meander-line slow wave structures (MLSWSs) is studied for application in Ka -band traveling-wave tubes (TWTs). Simulated dispersion characteristics and coupling impedance are presented for an optimized design. Particle-in-cell (PIC) simulation results show that for a 3.6-kV, 50-mA sheet-beam, the output power can potentially reach 28 W at 32 GHz with a gain of 28- and a 3-dB bandwidth of about 25% centered at 32 GHz. The proposed configuration is realized by first microfabricating a number of V-shaped MLSWSs on a 4” quartz wafer and then laser-dicing individual SWSs. A metal enclosure with waveguide input-output couplers is fabricated to house the SWSs and facilitate measurements. With two of the SWSs placed symmetrically inside the metal enclosure, the measured S11 for a 150-period symmetric MLSWS is better than -15 dB over 24-40 GHz. The reasons for the measured S21 being higher than expected are identified and verified by measurements on another set of SWSs which is fabricated using printed-circuit technique. An assembly that can be used for hot-tests is also presented.