A novel MMIC frequency doubler using a GaAs-based pHEMT process is proposed to achieve a miniature area and simplified layout. The circuit configuration is composed of a spiral balun, two common-source transistors, and a band pass filter with a dc-isolated capacitor, for an 18-38 GHz broadband operation. Both the spiral balun and the band pass filter are directly connected to the DC bias. The topology of the frequency doubler can thus be simplified to reduce the use of the bias components, such as the inductor. Thus, this doubler design of the chip size was considerably small and the operating bandwidth was wide. The spiral balun with bias also provide to suppress the fundamental frequency and reduce chip dimension. The fabricated frequency doubler results in a compact core chip size of 0.50 mm 2, a 0.5-5 dB conversion loss, and an output power of 5 to 9.5 dBm at an input power of 10dBm.