Generating an Energy Efficient Discrete Chirp Signal for UWB Chipless RFID Reader Circuit
The radio frequency identification (RFID) technology utilizes the radio frequency (RF) wave for identification of
a tagged object. The chipless RFID system operates in the microwave band and exploits the ultra-wideband (UWB)
technology. Though the reader of this type RFID system comprises a sophisticated electronic circuitry, the tag does not
contain any electronic circuits or silicon chip. The chipless tag is a special arrangement of numbers of microstrip resonators
together with antennas, and each resonator represents a logical bit 1 or 0. The detection methodology for microstrip resonator
type tag relies on a constant and continuous linear chirp from the UWB RFID reader. The entire UWB (7.5 GHz) needs to be
continuous frequency sweep or chirp to detect all the bits from the tag. However, when the bandwidth goes up to 4 GHz it is
difficult to generate a continuous linear chirp and the reader circuit becomes complicated. Alternatively, for detection of a
particular microstrip resonator or a bit on the tag, only concerning frequency of the microstrip resonator is needed and
consequently, the other frequencies are not being used. An electronic nonlinear frequency mixer circuit utilizes two different
frequencies and produces many new frequencies with the summing and differencing of the original frequencies. The desired
frequency can be extracted by using a narrow bandpass filter. Therefore, some required frequencies relevant with the
microstrip resonators (bits) in the tag can be generated by cascading the frequency mixer and the filter circuits. The
generation is only limited on those concerning frequencies allocated for the bits. As a result, the data bit from a tag can be
read without using a continuous frequency sweep in the entire UWB. Moreover, the procedure is simple and energy efficient.
In this paper, a new approach has been proposed to design an RF front-end for the chipless RFID reader circuit where the
continuous chirp is not essential. The design has been verified by using standard microwave simulation software. Four
different frequencies each successively 200 MHz apart have been generated in the UWB. The output power has been
observed for each discreet frequency aimed at a balanced load.
Keywords - UWB, RFID, Microstrip Resonator, Frequency Mixer, Narrow Bandpass Filter, RF Front-End, Balanced Load.