New techniques, employing spatial combining, enable high power and flat gain over a broad bandwidth. Spatial combining can be used to sum a much larger number of amplifiers over a decade-wide frequency range, than would be practical using conventional planar circuit techniques.
For example, an amplifier cell can be created using tapered-gap antipodal finline baluns2 to transition microstrip to a balanced finline structure suitable for launching into a coaxial waveguide. Antipodal finline is a balanced planar transmission line structure where two conducting strips of metal, separated by a dielectric substrate, are offset by a typically small gap (see Figure 2). Antipodal finline can provide a wide range of characteristic impedances. Closed form design equations for this transmission line media are not available; however, if the dielectric media is thin, and the gap is large, the design equations for unilateral finline can be used as an approximation.