A planar flexible radio-frequency, RF, tag for use in a real-time location system, the planar flexible RF tag comprising: a flexible substrate; a planar complementary patch antenna comprising first and second antenna patches and a differential input, the first and second antenna patches being positioned on a first side of the flexible substrate; an RF transmitter circuit positioned on the flexible substrate and having a differential output electrically coupled to the differential input; and a microcontroller circuit positioned on the flexible substrate and electrically coupled to control the RF transmitter circuit to drive the planar complementary patch antenna to transmit a radio signal; characterized in that it further comprises: a first decoupling circuit positioned on the flexible substrate and electrically coupled to the first antenna patch; a second decoupling circuit positioned on the flexible substrate and electrically coupled to the second antenna patch; a full-wave rectifier positioned on the flexible substrate and having a first half electrically coupled to the first decoupling circuit, and a second half electrically coupled to the second decoupling circuit; and a charging regulator circuit positioned on the flexible substrate and electrically coupled to the full-wave rectifier to receive power, via the first and second antenna patches, from a charging device that capacitively couples to the first and second antenna patches. a flexible substrate; a planar complementary patch antenna comprising first and second antenna patches and a differential input, the first and second antenna patches being positioned on a first side of the flexible substrate; an RF transmitter circuit positioned on the flexible substrate and having a differential output electrically coupled to the differential input; and a microcontroller circuit positioned on the flexible substrate and electrically coupled to control the RF transmitter circuit to drive the planar complementary patch antenna to transmit a radio signal; characterized in that it further comprises: a first decoupling circuit positioned on the flexible substrate and electrically coupled to the first antenna patch; a second decoupling circuit positioned on the flexible substrate and electrically coupled to the second antenna patch; a full-wave rectifier positioned on the flexible substrate and having a first half electrically coupled to the first decoupling circuit, and a second half electrically coupled to the second decoupling circuit; and a charging regulator circuit positioned on the flexible substrate and electrically coupled to the full-wave rectifier to receive power, via the first and second antenna patches, from a charging device that capacitively couples to the first and second antenna patches. a first decoupling circuit positioned on the flexible substrate and electrically coupled to the first antenna patch; a second decoupling circuit positioned on the flexible substrate and electrically coupled to the second antenna patch; a full-wave rectifier positioned on the flexible substrate and having a first half electrically coupled to the first decoupling circuit, and a second half electrically coupled to the second decoupling circuit; and a charging regulator circuit positioned on the flexible substrate and electrically coupled to the full-wave rectifier to receive power, via the first and second antenna patches, from a charging device that capacitively couples to the first and second antenna patches.