Abstract: An emitted wave is transmitted from a central station to a passive end. A phase modulation circuit in the passive end modulates a signal resulting from the emitted wave for retransmitting it in the form of a two-phase-state modulated signal at the rhythm of a clock signal. In the central station, the modulated signal is demodulated into two quadrature signals. On the basis of the product of the two quadrature signals and the sign of the difference between the moduli of the rectified quadrature signals, the count of an up-down counter in a digital processing circuit is incremented or decremented in order for said count to be representative of the distance separating the passive end and the central station.

Abstract: The radio system embodying the invention comprises a central station and a passive terminal station. First and second data signals are transmitted between data processing units respectively connected to the central and terminal stations. The terminal station comprises a same low-cost circuit associated with a square two-dimensional antenna for detecting the amplitude of a first incident microwave emitted by the central station thereby recovering the first data signal and deriving, in response to the first microwaves, a microwave modulated in phase by the second data signal by means of a retroreflection of a second incident microwave. This second incident microwave is emitted by the central station to the two-dimensional antenna of the terminal station. The terminal station is of very simple design, is compact and can therefore be included as well as the corresponding data processing unit in a contact-free chip card.

Abstract: The radio system embodying the invention comprises a central station and a terminal stations or passive end. Data signals are transmitted between data processing units which are respectively connected to the central and terminal stations. The radio system is essentially characterized in that the terminal station comprises a square two-dimensional antenna and a microwave switcher so as to phase modulate, by means of a data signal, a microwave transmitted from the terminal station to the central station. This phase modulated microwave is produced from an incident microwave transmitted by the central station and issued to the terminal station by the square two-dimensional antenna. The design of the terminal station is very simple and compact and can be included, as well as the corresponding data processing unit, in a contact-free chip card.

Abstract: A multifunction ultra-high frequency circuit and bidirectional transmission means using such a circuit. The circuit according to the invention comprises a directional coupler, two diodes, a transistor and an access connected to the diodes. The state of the transistor defines several functions of the circuit: modulation, mixing and transmission-reception separation. Application to half-duplex transmission.