Wideband antennas are capable of maintaining consistent near- and far-field performance over wide bandwidths. With the rapid growth of information technologies and ever increasing needs for high data throughput, these antennas become increasingly important for modern communication systems. However, many challenges arise in the design of wideband antennas and their use in different regions of the frequency spectrum.;Majority of wideband antennas designed for commercial applications nowadays operate at microwave frequencies, for which low-cost and low-profile are often as important as antenna's consistent electrical performance. This thesis first proposes a new feeding method to increase the bandwidth of the inherently narrowband patch antennas, the workhorse of modern communication industry. Compared with the previously published approaches, the proposed feeding technique delivers significantly increased impedance and far-field bandwidths, while maintains the antenna's low-cost and low-profile properties. The associated challenges including radiation pattern degradation, mutual port couplings, and electrical sensitivity on structural variations are thoroughly discussed and carefully addressed.;Considering the congestion of lower microwave spectrum, modern wireless systems are often designed for millimeter-wave spectrum. Typically they require wideband millimeter-wave antennas capable of seamless, preferably monolithic integration with the system's electronic circuitry. Recent advances in micro-electro-mechanical technologies have contributed to the development of micromachining processes capable of achieving many desired features of millimeter-wave systems. The second part of the thesis demonstrates millimeter-wave log-periodic dipole array (LPDA) antennas designed for and fabricated with a thick photolithography manufacturing process. It is shown for the first time that millimeter-wave LPDA antennas can be reliably achieved in the millimeter-wave region. It is also demonstrated that it is possible to monolithically integrate different devices within the LPDA antenna without impacting the antenna performance. For low-cost dual-polarized wideband antenna solutions, millimeter-wave planar log-periodic antennas fabricated using printed circuit board (PCB) process are also investigated as an alternative to the LPDA antennas.;Finally, wideband on-chip optical antennas are demonstrated for low-loss low-latency optical interconnects for the next generation microprocessor multi-core systems. Due to the high metallic loss at these frequencies, silicon-on-insulator based dielectric antennas are developed and over 50THz bandwidth is demonstrated. Based on the designed optical antennas, wideband optical signal hubs for wavelength-division-multiplexed (WDM) channel interconnects and data broadcast are developed. Theoretical study shows the proposed interconnect solution provides significantly increased power efficiency compared with the traditional electrical interconnect solution.
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