The field of the invention relates to the field of Radio Frequency (RF) transponders (RF Tags) which receive RF electromagnetic radiation from a base station whether or not the RF tags have a battery (which may be charged by the received RF energy), and send information to the base station by modulating the load of an RE antenna,
There are many wireless communication applications in the prior art that use mobile communication units. One application area is radio frequency identification (RF ID) systems, which involve a large number of these mobile units. A mobile antenna is an antenna that is attached to an article capable of moving.
There is a desire to minimize the cost of these mobile units, particularly when, such as in RF ID, there are a large number of mobile units in a system. While a battery is a reliable way to supply power to these mobile units, there are significant manufacturing costs incurred in using this device. Furthermore, batteries dictate certain shapes of the mobile unit, occupy area on the mobile circuit, and reduce the mechanical flexibility of the mobile circuit.
Passive mobile circuits exist in the prior art that have no battery supplying power to the circuit. These passive mobile circuits use the antenna structure on the circuit to seize energy from an electromagnetic field received by the passive circuit. The antenna used the energy in the field to provide the passive circuit with the power (both energy and voltage) to operate. In addition, these antennas detect (field detection) the presence of the electromagnetic field and may re-radiate a signal.
Typical field probing antennas in the prior art are made of short (non-resonant) dipoles loaded with a diode that is connected to the signal processing equipment (part of the mobile circuit) via a pair of high-impedance leads. These field-probing antennas are designed to minimize the disturbance to the field being detected.
One fundamental problem with passive tags is that the range is limited by the voltage picked up by the tag antenna and rectified by the tag power conditioning circuits. The voltage must be high enough to run the tag electronics, and the voltage is generally the limiting factor in determining the distance from the base station antenna at which the tags may be used. Even active tags having a battery to run the tag electronics are limited in the voltage picked up by the tag antenna.
Included are several variations of a mobile power antenna. Disclosed are resonant antennas coupled to a half wave rectifier, a full wave rectifier, and a voltage multiplier. This disclosure also shows a cascaded antenna. Additionally, planar elements can be added to these antennas to increase efficiency without reducing mobility.
The present invention also relates to a system, apparatus and method to use multiple antennas to receive RF power and signals from a base station, where circuitry is provided which will cascade the DC voltages produced by rectifying the signals at each of the multiple antennas.
An object of this invention is an improved antenna for powering a passive circuit on a mobile unit. A second object of this invention is an improved antenna for powering a passive circuit on a mobile unit when the antenna is non-resonant with the received frequency. A third object of this invention is an improved antenna for collecting power from an electromagnetic field of minimal power. A fourth object of this invention is an improved antenna and associated circuit for generation of a voltage from an electromagnetic field of minimal power.