Low-loss Lange coupler

The Lange coupler is used to make hybrid 3 dB couplers. In order to equalize the odd- and even-mode phase velocities, bond wires have to be used to join alternate lines of the coupler. In monolithic circuits the incorporation of bond wires is not possible, and techniques have been developed which involve the replacement of bond wires by air bridges. The present investigation is concerned with a comparison of the loss associated with air-bridge and wire-bonded couplers on alumina. It is found that the use of air-bridge straps on Lange couplers constructed on alumina gives couplers with a transmission loss which is lower than that observed in the case of an identical coupler using bond wires. The air-bridge technique also makes the mass production of circuits employing Lange couplers easier. The assembly step of bonding the coupler is eliminated at the expense of an extra fabrication step.