Development of a switching passive 2.4 GHz RFID transponder on flexible substrate

For the detection and tracking of a football on a playground, a transponder was developed on a flexible substrate suitable for integration in the ball. The transponder secures permanent detection and identification with FMCW radar, thus enabling an easy and cost-effective tracking of the ball. The transponder consists of a dipole antenna and a microprocessor controlled switch which shorts at a programmable rate the input port of the dipole. The user selectable switching frequency or switching sequence can be recognised in the radar Doppler spectrum, since the transponder´s received amplitude and phase vary between the on- and off-state. This approach is patented under nr. 07112606.4. The design, realisation and first results of the transponder are discussed in this article.