Novel Approach to Enhance Spectral Width of the Interrogating Signal for Reading Ultrawideband Chipless RFID Tags

In the state-of-the-art, the spectral width of the interrogating signal in frequency-domain RFID readers is the same as that of a voltage-controlled oscillator (VCO). The amount of information extracted from the tag is limited by the bandwidth of the VCO. However, VCOs with wider bandwidth are an expensive solution. In this paper, we propose a novel RFID reader approach that utilizes only a 1.2-3.6 GHz VCO in conjunction with two mixers to generate an interrogating signal with a frequency range of 1.2-10.8 GHz. This way, it achieves an interrogating signal fractional bandwidth of 160% thus providing a low-cost solution for commercial applications. A 24-bit lumped circuit model of a microstrip chipless RFID tag is exploited to illustrate the effectiveness of the proposed reader approach. The fractional bandwidth of the interrogating signal is analytically derived and compared with the current state-of-the-art.