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This paper deals with a low-cost method for the assembly of flexible substrate antennas and UHF RF identification silicon (Si) chips. Such a method exploits a magnetic coupling mechanism, thus not requiring for galvanic contacts between the Si chip and antenna itself. The magnetic coupling is established by a planar transformer, the primary and secondary windings of which are implemented on flexible substrate and Si chip, respectively. As a result, the Si chip can be assembled on the antenna with a mere placing and gluing process. First, the idea has been validated by theory. Electromagnetic simulations of a square heterogeneous transformer (1.0-mm side) show a maximum available power gain (MAG) of -0.4 dB at 868 MHz. In addition, the heterogeneous transformer is also quite tolerant with respect to misalignment between primary and secondary. An offset error of 150 μm reduces the MAG to - 0.5 dB. A sub-optimal matching strategy, exploiting a simple on-chip capacitor, is then developed for antennas with 50- Ω input impedances. Finally, the idea has been experimentally validated exploiting printed circuit board (PCB) prototypes. A PCB transformer (1.5-mm side) and a transformer rectifier (two-diode Dickson multiplier) have been fabricated and tested. Measurements indicates a MAG of -0.3 dB at 868 MHz for the transformer and the capability of the developed rectifier to supply a 220-kΩ load at 1.5 V with a - 2-dBm input power.