Realizzazione di un beamforming analogico per sistemi RFID

The job developed in this thesis has been that to plan an electric circuit that realize an analog beamforming with two dipole spar, related to the receiving chain of the systems RFID, in the UHF (860÷868 MHz) frequencies band. Such a project puts in evidence a solution of system and the realization of the circuit it is a part of it. In fact the use of two spar allows to increase the general profit in comparison to a single spar and therefore to exploit such advantage for the range of action of the device or to parity of this last to decrease the power in transmission. The circuit reduces to zero the phase between the signals received by the two spar allowing to drive the principal lobe of the diagram of spar in direction of the transmitter or rather that of maximum field of radiation, so maximizing the received signal. The circuit is constituted by varicap diodes which inversely polarized works as capacitances controlled in voltage. The same function is developed by the MOS varactor but the choice of the diodes it is due to the fact that in the MOS varactor the variation of the capacitance is at the most of 2 pF while with the varicap they reach variation of 15-18 pF allowing to reduce to zero the phase between the signals on a greater range of delays. This allows us to check and to reset the bewilderment among the induced signals around two spar making to vary the voltage of polarization. This happens changing the phase of the received signal by one of the two spar of 90° through a net realized with the diodes opportunely polarized in the point of select rest in a linear zone of the characteristic ability-tension of the varicap. Then the signals are opportunely amplified and multiplied. The output of the multiplier is filtered getting a value of proportional continuous tension to the bewilderment of the two signals. This tension is applied, in reaction, on the diodes making to vary their polarization, therefore the value of their ability until to reduce to zero the difference of phases. To this point the value of the continuous tension to the output of the multiplier is void, we have so corrected the error of phase. To correct the error of phase means to aim the lobe of radiation of the spar in the direction of maximum field. The circuit corrects a bewilderment among the signals equal to 0.15 ns. The two spar allow us to get a double profit in comparison to the single spar. This allows us to choose whether to decrease the power in transmission of 2 or to increase the range of action of the device, practically than in base to the equation that exists between the power of transmission and the power in receipt among two spar, a transmitting station and the other receiver. The circuit in matter, being realized with discreet components has enough elevated consumptions of power, 12 V of power supply, as well as the noise and the parasitic capacitances are greater in comparison to an integrated device. For this reason in a future development of integrated circuit realization on silicon, the required amplifications will surely be smaller and therefore to reduce notably the consumption of power. This will also allows the use of such a circuit on the semipassive or active tags. At present, the component discreet electric scheme of the design surely allows the use in the reader.