Editing Wireless power transfer (section)

=== Post-war developments ===

Before World War II, little progress was made in wireless power transmission.<ref name="Brown1984"/> [[Radio]] was developed for communication uses, but could not be used for power transmission since the relatively low-[[frequency]] [[radio wave]]s spread out in all directions and little energy reached the receiver.<ref name="Shinohara" /><ref name="Brown1984"/> In radio communication, at the receiver, an [[amplifier]] intensifies a weak signal using energy from another source. For power transmission, efficient transmission required [[transmitter]]s that could generate higher-frequency [[microwave]]s, which can be focused in narrow beams towards a receiver.<ref name="Shinohara" /><ref name="Brown1984"/><ref name="Curty">{{cite book |last1=Curty |first1=Jari-Pascal |last2=Declercq |first2=Michel |last3=Dehollain |first3=Catherine |last4=Joehl |first4=Norbert |title=Design and Optimization of Passive UHF RFID Systems |publisher=Springer |date=2006 |page=4 |url=https://books.google.com/books?id=uFjpH3Cl7z8C&pg=PA4 |isbn=978-0387447100}}</ref>

The development of microwave technology during World War II, such as the [[klystron]] and [[magnetron]] tubes and [[parabolic antenna]]s,<ref name="Brown1984"/> made some radiative ([[Near and far field|far-field]]) methods practical for the first time, and the first long-distance wireless power transmission was achieved in the 1960s by [[William C. Brown]].<ref name="Shinohara" /> In 1964, Brown invented the [[rectenna]] which could efficiently convert microwaves to DC power, and in 1964 demonstrated it with the first wireless-powered aircraft, a model helicopter powered by microwaves beamed from the ground.<ref name="Brown1984"/>