Multichip modules are important to the advancement of modem high-performance radar, communication, and navigation systems. Besides improved electrical performance, these modules offer reductions in weight, enhanced thermal and mechanical characteristics, and improved reliability. With the growing need for smaller, lighter electronics for spaceborne and defense applications, the Applied Physics Laboratory is using state-of-the-art design software, materials, and microelectronics fabrication techniques to build multichip modules for advanced microwave applications. This article describes two of these applications: a 14-GHz transmit and receive module and a 32-GHz active antenna array. These advanced design and packaging initiatives have demonstrated the dramatic reductions in size and weight that their application to modem electronics systems can achieve.