Phased array radar system developments using X-band transmit/receive (T/R) module technology are summarized. Requirements are developed from systems concepts for fighter aircraft radar applications. Factors influencing system performance are discussed in terms of the allowable tradeoffs that must be considered for deployable systems. T/R module architectures are investigated in light of the system derived performance requirements. These module requirements are reduced to the individual circuit function level, and examples of circuits developed to meet these requirements are presented. Critical T/R module technologies are discussed in view of the latest developments in microwave active and control devices, manufacturing assembly processes and equipment, package materials and fabrication processes, and test automation. Module developments during the past 25 years are discussed chronologically and described in terms of the performance characteristics attained. Test requirements unique to module integration and aperture-level performance verification are highlighted. Module price targets are derived from affordability constraints imposed by the fighter aircraft radar application.>