The postwar period foregrounded vacuum-electron devices as the primary means of generating and amplifying microwave energy, accompanied by growing emphasis on space-charge effects, stable high-frequency performance, and the deployment of these devices in radar and communication infrastructure. A parallel thread pursued the development of planar transmission concepts, as reflected in early microstrip ideas, and systematic antenna theories that translated laboratory advances into practical, efficient microwave hardware. Methodologically, the era combined experimental refinement with evolving models of wave propagation and spectral behavior to support rapid technology transfer across military and civilian applications. Historical Significance: This era laid the foundation for microwave engineering by establishing electron-wave tube technology as the workhorse device, introducing planar microstrip paradigms that would grow into modern RF circuits, and revealing the potential of transit-time effects and negative resistance for compact oscillators. The period's breakthroughs also seeded generalized collision-broadening insights that informed spectral analysis and remote sensing, connecting the microwaves field to broader electromagnetic theory and enabling future progress in solid-state and integrated microwave technologies.