This paper presents a complete top-down design and experimental results for a fast-hopping 11-band 3-10-GHz frequency synthesizer. The system requirements for a synthesizer in an ultrawideband (UWB) radio are discussed. The synthesizer specifications for 480-Mb/s- and 1-Gb/s-data-rate multiband orthogonal-frequency-division-multiplexing UWB radios using quadrature phase shift keying and 16-quadrature amplitude modulation, respectively, are provided. The circuit-level implementation of this microwave system is described in detail including layout considerations. Fabricated in a 0.25-mum SiGe BiCMOS process and integrated in a receiver, the synthesizer was characterized in a quad-flat-no-leads package while being mounted on an FR-4 substrate. Measurement results and a model-hardware correlation analysis are presented.