In conventional wireless and microwave communications, voice or data signals are exchanged between the users, suppliers, or both. The wireless communications need not be limited to information signals alone. Power can also be transmitted or exchanged. This possibility will extend the use of wireless systems to many new applications, simplify hardware designs, and remove the current requirement of wireless communication channels for locations with available power, or batteries. The latter places severe limitations on the use of wireless networks and prevents innovation in the related technologies and applications. In addition, the availability of wireless power will expand the use of wireless sensors to many new areas in remote sensing and medicine. It will also enable innovations in non-communication-related technologies such as transportation, unmanned aerial vehicles, and mechanical systems.
The technology of wireless power transmission is currently known as microwave power transmission (MPT), or “energy harvesting.” While the former deals with any wireless power transmission, the latter refers mostly to small power levels. Historically, MPT has dealt with large power transmissions. Small power transmissions were not considered, mostly because wireless devices were not widespread and the power requirements of electronic devices were large. However, many new devices and technologies need small power levels to operate. Thus, energy harvesting is currently the primary area of interest, and this chapter will address the antenna designs for its applications, in particular antennas that can share both power and communication channels concurrently. However, since most research in the literature deals with communication antennas, for completeness a historical background is provided, to review the steps in the development of MPT, and the role of the antennas in its development. This is followed by a review of different antenna types that are useful for both energy harvesting and communications, and a few design examples.
In selecting the design examples effort is made to choose antennas with low-profile structures, having geometries compatible with technologies for both passive and active devices, mass production techniques and low-cost fabrication. In addition, since most innovations in communication, remote sensing and medical applications deal with small sizes, the design examples are selected to have potential for antenna miniaturizations. However, the actual antenna miniaturization techniques are not discussed in this chapter.