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Active antenna for two-way transmission

  • US 5,280,633 A
  • Filed: 03/14/1991
  • Issued: 01/18/1994
  • Est. Priority Date: 03/27/1990
  • Status: Expired due to Term
First Claim
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1. An active antenna for the two-way transmission of information, by the modulation/demodulation of a microwave carrier, between a central station that sends out first modulated interrogation signals and a terminal station that responds to said central station by second modulated signals, the terminal station including said active antenna, wherein a modulation/demodulation means or modem of said antenna includes a transistor to which a bias current (Ids) is applied, said bias current being switched over between a value that is low at reception, with the transistor being in the detector/demodulator state, and a value that is high at transmission, with the transistor being in the amplifier/modulator state.wherein the circuit for switching over the bias current of the transistor is constituted by three resistors (Rd, Rgd, Rg) with high values, series-connected between the two poles (+V, -V) of a voltage supply, the second resistor (Rgd) of this series being connected between the gate and the drain of the transistor, wherein the source of the transistor is grounded, said three resistors (Rd, Rgd, Rg) being switched over from a high value in the demodulation state to a low value in the modulation state by means of a pair of transistors controlled by two switch-over signals that alternately take the positive (+V) and negative (-V) values of the supply.

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