Dielectric slab based spatial power combiners

Spatial power combiners have the potential for realization of moderate power sources at millimeter wavelengths by summing the output signals of large numbers of solid-state devices. Most previous work has focused on three-dimensional approaches, such as the wave beam type, grid type, microstrip coupling type, and lens type. A quasi-optical structure based on the dielectric slab-beam waveguide (DSBW) is two-dimensional and therefore more amenable to planar fabrication technologies. An oscillator and several amplifiers based on the DSBW have been reported. These structures excited an electric field parallel to the slab ground plane. Such a mode has very low loss but is difficult to excite cleanly with no perturbation or scattering loss. Dielectric lenses were used to focus and constrain the guided waves. Both the TM and TE surface wave combiners described herein use microstrip delay lines to focus the guided waves in a manner similar to that reported by Schoenberg, Bundy and Popovic (see IEEE Trans. on Micowave Theory and Techniques, vol.MTT-42, p.2480-5, 1994). The delay line length is analogous to the thickness of a conventional dielectric lens. Commercial gain blocks are used to amplify the RF signals. Yagi-Uda slot antenna arrays, fed by microstrip lines, were used to efficiently excite the dominant TM surface wave mode with the electric field normal to the slab ground plane. A microstrip to parallel strip balun was used to feed a dipole antenna and launch TE surface wave in a homogeneous slab. TE and TM surface wave power combiners with net system gain and reasonable bandwidth have been demonstrated.