A microstrip re-entrant mode quadrature coupler for hybrid and monolithic circuit applications

The reentrant mode TEM (transverse electromagnetic) coupling method allows the MMIC (monolithic microwave integrated circuit) design engineer to fabricate low loss couplers on either GaAs or Al/sub 2/O/sub 3/ substrates without the problems encountered in fabricating long fine-line structures. In addition, since the odd mode energy is mainly contained in a high-dielectric region rather than in air, the even and odd mode velocities are closely matched, thus enabling the coupler to exhibit excellent VSWR (voltage standing wave ratio) and differential phase performance. Because of the excellent coupler performance and design flexibility obtained with this technique, coupled structures which used to require multilayer stripline or suspended substrate approaches can now be easily fabricated and integrated with conventional MIC (microwave integrated circuit) circuitry. The technique also allows the MMIC designer to fabricate very tightly coupled structures without the problems encountered with fine-line lithography.<>