A major problem facing Planet
Earth is provision of an adequate supply of clean energy. It has been that we
face "...three simultaneous challenges -- population growth, resource consumption,
and environmental degradation -- all converging particularly in the matter of
sustainable energy supply." It is widely agreed that our current energy practices
will not provide for all the world's peoples in an adequate way and still leave
our Earth with a livable environment. Hence, a major task for the new century
will be to develop sustainable and environmentally friendly sources of energy.
Solar power from the satellite is sent to Earth using a microwave transmitter. This transmission is transmitted to the relevant position via an antenna. The transmission is transmitted through space and atmosphere and received on earth by an antenna called the rectenna. Recent developments suggest using laser by using r ecently developed solid state lasers allow efficient transfer of power. A range of 10% to 20% efficiency within a few years can be attained, but further experimentation still required taking into consideration the possible hazards that it could cause to the eyes. In comparison to laser transmission microwave transmission is more developed, has high efficiency up to 85%, beams is far below the lethal levels of concentration even for a prolonged exposure. The microwave transmission designed has the power level well below the international safety standard (Frequency 2.45 GHz microwave beam). The electric current generated from the photovoltaic cells is passed through a magnetron which converts the electric current to electromagnetic waves. This electromagnetic wave is passed through a waveguide which shapes the characteristics of the electromagnetic wave.
Effectiveness of Wireless Power Transmission (WPT) depends on many parameters. Only a part of WPT system is discussed below, which includes radiating and receiving antennas and the environment between them. The wave beam is expanded proportionately to the propagation distance and a flow power density is increased inversely proportional to the square of this distance. However the WPT has some peculiarities, which will be mentioned here. WPT systems require transmitting almost whole power that is radiated by the transmitting side. So, the useful result is the power quantity at the receiving antenna, but not the value of field amplitude as it is usually required. Efficiency of WPT systems is the ratio of energy flow, which is intercepted by receiving antenna to the whole radiating energy.
Field distribution on the receiving antenna usually is uniform because its size is small comparatively to the width of the beam. For WPT systems this distribution isn't uniform. It has a taper form and it depends on the field distribution on the transmitting antenna.
For increasing of the energy concentration on the receiving antenna the phase distribution on the radiating antenna has usually a spherical form with the center in the point on crossing of the receiving plate and the radiating axis. Radiating antenna of the WPT systems usually has a taper distribution of the field. This distribution allows to increase the efficiency and to decrease the field out of the receiving antenna.
The efficiency of energy transmission is expressed by the functional ? 2 . To increase ? the field distribution on radiating aperture is made as a tapered distribution. High value of ? is supposed to be in the majority of known projects of the WPT systems.