Active antenna for bidirectional transmission.

This active antenna is incorporated in the terminal station of an information exchange system with a central station by modulation of a microwave carrier. The terminal station is card type chip. The modem of the active antenna is constituted by a transistor (10) whose bias current is switched from a low value to demodulation at a high value to the modulation. Switching is achieved by means of a circuit of three resistors (Rd, Rg, Rg), themselves switched values ​​by two transistors (13, 14) connected in parallel with the resistors, these transistors being controlled by two signals ( M1, M2) transmitted by the terminal station control circuit. Applications: Remote data exchange such as electronic toll collection, remote ticketing, mobile location etc ... .