Wireless power transfer is a technique of power supply for
some special applications. Since the first wireless power
transmission (WPT) system was demonstrated in 1958 [1, 2], it
has become an increasingly interesting topic for wireless
engineering community. One of the most important elements in
this technique is the rectenna which is the combination of an
antenna and a rectifier and it is composed by a receiving
antenna and rectifying circuit to covert electromagnetic energy
to direct current (DC) energy. Some rectennas have already
been developed but most of them are linearly polarized and of
a narrow bandwidth. Most researches have focused on single
element rectenna design [3]. With the rapid development of
various wireless systems, there have been many wireless
systems developed and installed in our cities. The radio
frequency (RF) power in the environment has increased
significantly. For example, we can easily receive TV, cellular
radio, and WiFi signals, and the RF power density has become
quite considerable in many areas. How to recycle or collect
these transmitted RF signals has become a subject of increasing
interest, there is a need of using a broadband rectenna array
with dual polarization to harvest these RF energies.