37.1-dBm W-Band Power Amplifier Module Using GaN-Based HEMTs Stabilized With Resistive Back Metal for Broadband Wireless Applications

Abstract

This letter presents a four-way W-band power amplifier (PA) module that packages GaN-based high electron mobility transistor (HEMT) millimeter-wave monolithic integrated circuits (MMICs) designed with coplanar waveguides (CPWs). A resistive-back-metal (RBM) layer was formed on the back side of the MMICs to keep stable in the module even without using substrate vias. The verification of the effect of the RBM layer was performed using CPW-based MMIC test chips. The assembled PA module, where millimeter-wave components, such as a waveguide (WG) combiner/divider and a WG-to-microstrip line transition, were optimized to reduce losses and flatten frequency responses, demonstrated stable and broadband characteristics in a frequency range of 88–100 GHz. A peak output power ( $P_{\text {OUT}}$ ) of 37.1 dBm with a power-added efficiency (PAE) of 9.9% was achieved at a frequency of 92 GHz and a bias voltage ( $V_{\text {DS}}$ ) of 15 V. $V_{\text {DS}}$ was set to 20 V to enhance the power performance of the PA module, achieving a peak $P_{\text {OUT}}$ of 38.8 dBm with a PAE of 8.1%. To the best of our knowledge, the PA module exhibited the highest peak $P_{\text {OUT}}$ value among W-band single PA modules with a bandwidth (BW) of more than 10 GHz.