Investigation of planar antennas with photovoltaic solar cells for mobile communications

This paper describes the application of photovoltaic (PV) solar cells in planar antenna structures. The radiating patch element of a planar antenna is replaced by a solar cell. Furthermore radiating slots are built due to the cell spacing in a solar cell array. The original feature of a solar cell (DC current generation) remains, but additionally the solar cell is now able to receive and transmit electromagnetic waves. Both single solar cells as well as solar cell arrays can be used as antennas. At first some basics regarding the RF properties of solar cell patches are discussed. The efficiency of solar cell antennas is measured by means of the Wheeler Cap method, which is investigated by means of numerical simulations. The lossy substrate of the feed lines has the strongest influence on the antenna efficiency. Finally two applications are presented: a solar cell GPS antenna for vehicular applications and a solar cell slot antenna for mobile communications (GSM). The aim is to integrate these antennas into vehicular glass roofs which are covered with photovoltaic solar cells in order to deliver the electric power for the indoor ventilation of the car. The GPS antenna provides circular polarisation and a main lobe in zenith direction whereas the GSM antenna is vertically polarized and has a monopole-like radiation pattern. Both antennas are built up with commonly used solar cells. The comparison of measured and simulated antenna properties shows a good agreement.