This thesis presents a unique view on radio systems that can simultaneously function at multiple frequency bands. These radios offer a higher data-rate and robustness in addition to the added functionality in the performance of wireless systems. Our treatment includes the definition of such novel radios, formulation of their singular characteristics, proposition for transceiver architectures, and invention of circuit blocks.Various transceiver architectures for this new class of concurrent multi-band radios are proposed. The results for an integrated concurrent dual-band receiver operating at 2.4 GHz and 5.2 GHz frequency bands for wireless networking applications are presented. Meticulous frequency-planning results in a high level of integration and a low power design for the concurrent receiver. Several new circuit concepts including the concurrent multi-band low-noise amplifier are demonstrated in this design. A general class of these concurrent multi-band amplifiers is investigated with numerous implementations of integrated concurrent dual-band and triple-band amplifiers.A theoretical treatment of nonlinear oscillators with multi-band resonator structures is also offered. It is shown that given certain nonlinearities these oscillators can generate multi-frequency outputs. The phase-noise of such negative-resistance oscillators with general resonator structure is addressed. By providing a link between the stored and dissipated energies of a network and its associated circuit parameters, useful interpretations of resonator quality factor are derived. With the aid of this analysis and the previously developed phase-noise models, dependencies of phase-noise on the resonator structure are derived. Based on our theoretical results, enhanced resonators with higher quality factor providing a superior oscillator phase-noise are proposed.Finally, in order to enhance the performance of wireless systems by exploiting the spatial properties of the electromagnetic wave, multiple-antenna radios in phased-array configuration are investigated. The phased-array technology results in higher immunity to unwanted interference and therefore achieves a superior overall system capacity in a shared environment. The first fully integrated multiple-antenna receiver targeting the 24 GHz ISM band using silicon technology is presented. The phased-array radio at 24 GHz is a cheap solution for high data-rate WLAN, as well as for fixed wireless broadband access applications.
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