A Lumped-Element Wideband 3-dB Quadrature Hybrid

A novel lumped-element topology is presented for a wideband 3-dB 90° hybrid coupler where design and implementation are straightforward. In the design, only lumped LC elements are used, and the topology employs a simple widebanding technique. Depending on the allowed ripple, theoretical bandwidths up to 80% are achievable. Both return losses and isolations are theoretically infinite at the center frequency and remain better than 15 dB over the band depending on the proper choice of design parameters. Design can be optimized with respect to bandwidth, passband ripple, and balance between output signals. To have common grounds at the ports, lattice-type LC baluns are used. Theoretically, the phase difference between output signals deviates less than 2° depending on the application. An X-band monolithic microwave integrated circuit (MMIC) is realized for the topology. The measurement results show that the circuit has a 49% bandwidth with 1.2-dB ripple and less than 6° phase deviation from 90° over the band.