With the evolving spectral allocations across bands ranging between 24-100 GHz, future mmWave front-ends will need to address multiple band allowing spectral agility and spectrum sharing capabilities for high capacity and robust links. Such characteristics are extremely challenging to achieve in transmitter front-ends particularly at the power amplifiers. This paper presents a broadband and efficient mmWave PA with Ptextsat,3dB bandwidth covering 30-97 GHz capable of supporting concurrent multi-band modulation operation. Implemented in GlobalFoundries 90 nm SiGe process, we employ common-base HBT transistors with broadband, yet highly efficient power combiner exploiting mix of open and short stub transmission line network. For single carrier CW operation, the proposed PA achieves 18.5-21.5 dBmPtextsat, 18-26% PAE across 106% bandwidth. We demonstrate one of the first concurrent multi-band mmWave modulation capability with three 32 QAM signals (total data rate up to 7.5 Gbps) across licensed/unlicensed spectrum of 36/39/66 GHz exhibiting 7.9/8.2/11.5 dBm linear average power and concurrent PAE of 11%. The PA exhibits one of the highestPtextsat,3dB bandwidth with peak output power exceeding 20 dBm, peak PAE greater than 25%, and concurrent multi-band capability allowing new capabilities in spectrum sharing, frequency diversity and always connected capability in resource-constrained environment.