Patent ID: 7917093

Claim:
A wireless monitoring system using a base station and a child station, comprising: said base station including: a base-station transmitting antenna for transmitting an electric power supplying carrier and a signal transmitting carrier to said child station; and a base-station receiving antenna for receiving an output from said child station; said child station including: a child-station receiving antenna which comprises a balanced antenna; a nonlinear circuit that receives an output from said child-station receiving antenna; a smoothing circuit that receives an output from said nonlinear circuit; a first high-frequency band-pass filter, a pass band of said first high-frequency band-pass filter comprising a frequency of said electric power supplying carrier; an intermediate-frequency band-pass filter, a pass band of said intermediate-frequency band-pass filter comprising an intermediate frequency which comprises a differential frequency between said electric power supplying carrier and said signal transmitting carrier; a demodulator that receives an output from said intermediate-frequency band-pass filter and uses an output from said smoothing circuit as a power source; a baseband circuit that modifies a baseband signal using an output from said demodulator; a modulator for modulating a high frequency signal outputted from said first high-frequency band-pass filter by using said baseband signal; and a child-station transmitting antenna for radiating an output from said modulator, wherein said base-station transmitting antenna and said child-station receiving antenna comprise circularly-polarized antennas which have a same rotating direction, and said child-station transmitting antenna and said base-station receiving antenna comprise circularly-polarized antennas which have a polarization characteristic rotating in a direction opposite to said base-station transmitting antenna and said child-station receiving antenna.