A major challenge for low-cost silicon-based mm-wave wireless links, e.g., for the 5G communication, is to provide large transmitter (Tx) output power (P _out ) with high energy efficiency and linearity from a limited supply voltage, so that the high path loss and limited link budget at mm-wave can be compensated. Power combining is often required for high-power mm-wave Tx. The existing power-combining techniques are mainly in two categories. Passive on-chip/on-package networks can combine P _out from multiple power amplifiers (PAs) and feed a single antenna port [1-4]. However, lossy power combiners and large impedance transformation ratios degrade the total P _out delivered to the antenna and lower the Tx efficiency. Alternatively, spatial power combining using antenna array increases the total EIRP but at the expense of a large array-panel size. Moreover, a large antenna array often presents an exceedingly narrow (or even pencil-sharp) beamwidth; this complicates the Tx/Rx alignment and is challenging for dynamic and mobile mm-wave applications, such as 5G links. In addition, adding silicon lens enhances EIRP but increases cost and packaging complexity.