GCPW GaAs broadside couplers at H-band and application to balanced power amplifiers

This paper reports on the first H-band broadside hybrid coupler based on a three-metallization layer process and a grounded coplanar waveguide environment. The performance of this integrated coupler is carefully examined through electromagnetic (EM) simulations and experimental evaluation, and compared to a Tandem-X hybrid, which is based on a two-metallization layer process and requires twice the chip area. The EM analysis covers S-parameter simulations of the coupler structures as well as even- and odd-mode impedance analysis of the edge- and broadside-coupled lines. The broadside hybrid exhibits insertion losses of 3.8-4.3 dB in the through and coupled ports from 246 to 297 GHz. This corresponds to a fractional bandwidth of 19%. In this frequency range, the imbalance is lower than 0.2 dB and a phase difference of 93.6° ± 1.4° is obtained. It is demonstrated that the broadside coupler overcomes the performance of Tandem-X hybrids when applied to medium power amplifiers (MPAs). An MPA monolithic microwave integrated circuit based on triple-stacked FETs and broadside couplers achieves at least 4.5 dBm at 300 GHz and large-signal gain of 7.5 dB at the 3-dB compression point.