Ultra-broadband high-directivity directional coupler design

The theory and design of ultrabroadband high-directivity tapered-line directional couplers are discussed. Causes of imperfect directivity are examined from both a theoretical and experimental standpoint. This includes the effects of nonunity VSWR terminations and internal connections, unequal even-mode and odd-mode velocities, and unequal even-mode and odd-mode attenuation constants. Practical considerations in the design of asymmetrical tapered couplers are discussed. A design example is presented which displays a bandwidth that is believed to be approximately 1.7 octaves greater than any other coupler of comparable directivity.<>