# Constraints of Using Conductive Screen-Printing for Chipless RFID Tags with Enhanced RCS Response
## 1 Introduction  
Radiofrequency identification technology (RFID) is widely used in a variety of applications, primarily in logistics, industry, and health care [1]. The modern Internet of Things paradigm is conditioned by the successful development of this concept mainly for wearable or metal-mountable solutions [2; 3; 4; 5], and sensing purposes [6; 7; 8; 9]. The relatively high price of the chipped RFID transponders impedes the further expansion of this technology. The chipless RFID [10] as a method of identification information storage without a semiconductor chip represents a promising way of reducing tag costs. The frequency-domain chipless RFID technology represents the most investigated solution, which potentially enables low-cost manufacturing by means of conductive ink printing. The frequency-domain chipless RFID tag is typically composed of an array of mutual detuned scatterers [11; 12; 13; 14; 15; 16; 17; 18]. The presence or absence of particular resonant peaks in the RCS response represent the logical one or zero, respectively. The description of a frequency-domain chipless transponder's behavior can be performed by two fundamental quantities, dependent on the _ka_ product. The radar cross section (RCS) level is the first one, and the quality factor \(Q\) determined by a 3 dB bandwidth of resonance peaks or drops is the second one. The power received at a potential reader of a chipless RFID transponder is directly proportional to the level of the RCS response, and is also inversely proportional to the distance of the reader from the transponder to be identified. Based on this fact, it is reasonable to expect that there will be a specific distance from which the lowest of the resonant peaks/drops of the RCS response will no longer be readable, leading to a fatal decrease in the readability of the entire tag. On the other hand, the quality factor \(Q\) is a crucial parameter of the chipless transponder resonators with respect to the spectral bit capacity. Given the above, we require the narrowest possible bandwidth per transponder resonator for frequency-domain chipless RFID. In other words, we require that the quality factor along with the overall RCS response level be as large as possible. This is a new perspective with respect to conventional antennaapplications. Similarly, for sensor tags, the bandwidth of the resonant dips, which is a key parameter for maximizing the resolution of the frequency shift and hence the sensitivity of the sensing structure, has to be reduced accordingly. The smaller the electrical size \(ka\), the lower the RCS response, and, concurrently, the higher the \(Q\). As a result, the higher spectral bit capacity, though at the expense of limited read range, is reached. The well-balanced trade-off of these parameters enables reliable identification of the chipless RFID tags in real conditions in conjunction with well-established measurement methods [19; 20]. The manufacturing of the transponders by a conductive inkjet- or screen-printing technology [21; 22; 23; 24; 25; 26] enables a further reduction of the price cost. Screen- and inkjet printing are forms of modern electronic fabrication technology that can bring a low-cost and environmentally friendly alternative to the common etching fabrication process [23; 26]. Due to the refinement of various printing materials, various planar radiating structures have been manufactured by screen-printing or inkjet printing on flexible or rigid substrates [23; 24; 25; 26]. However, the influence of reducing \(Q\), due to the lower conductivity of screen-printing to the frequency-domain chipless RFID tags properties mentioned above, has to be verified. In this paper, an analysis and experimental verification of the performance properties of tags with an increased RCS level (as a crucial parameter for identification in real conditions) designed and fabricated by means of conductive screen-printing was performed.