A new broadband monolithic passive differential coupler for K/ka-band applications

A new broadband monolithic passive quadrature differential coupler has been realized at millimeter-wave frequencies. The new coupler is implemented on a multidielectric layer structure to achieve a broadband performance from 15 to 45 GHz in a simple coplanar configuration. The coupler has been monolithically fabricated using the IBM SIGEHP (BICMOS 5HP) process. Measured return loss better than 20 dB, with an isolation of 15 dB, and adequate phase and amplitude mismatch have been achieved over 3 : 1 bandwidth centered at 30 GHz. This performance is especially important to the intended use with wideband double-balanced mixers and amplifiers. To shrink the overall coupler area, a slow-wave technique has been introduced, resulting in an overall size reduction of the coupler by almost 38%. The fabricated slow-wave differential coupler measured results show return loss better than 25 dB, isolation better than 15 dB, and phase and amplitude mismatch within plusmn5deg and plusmn1 dB, respectively