# Trade-Off Analysis for Array Configurations of Chipless RFID Sensor Tag Designs
## 1 Introduction  
Radio frequency identification (RFID) technology has gained significant interest in the past few decades due to its potential applications in various fields [1]. These traditional RFID tags use a microchip and a battery to store information and connect to wireless networks [2]. However, these wireless tags can be expensive, difficult to incorporate with wearable devices, and difficult to operate in harsh environments. As a result, chipless RFID technology has emerged as a promising alternative, as it can be produced at a lower cost and with greater flexibility in various applications, such as supply chain management [3], healthcare [4], environmental monitoring [5], food packaging [6], and structural health monitoring [7]. Unlike traditional RFID tags, chipless RFIDs do not have a microchip or energy source. Instead, they use unique patterns of resonant structures to encode sensing and identification (ID) information and extract energy from the interrogation signal. These patterns can be detected using a reader that transmits an electromagnetic (EM) signal to the tag, causing it to resonate and retransmit a unique EM signature that can be decoded to extract information [8]. Therefore, the resonator structure, the size of the tag, the quality(Q) factor, and the radar cross section (RCS) are the critical parameters that determine the performance and precision of the chipless RFID system [9]. In chipless RFID systems, the RCS parameter crucially influences the magnitude of the reflected signal, thus affecting the overall system performance [10]. In other words, it determines the magnitude of the reflected signal; therefore, the detectability of the chipless tags depends on it. In general, the RCS of chipless RFID tags depends mainly on the size of the tag [11]. Therefore, designing an optimised tag with a high RCS is essential to achieve reliable and accurate performance in real-world applications. Array configurations are the most promising approach to improving the RCS. This paper aims to analyse linear and planar array configurations to improve the RCS of the chipless RFID tag. In addition, the Q-factor also plays an important role in determining the resolution and detectability of chipless RFID tags and sensors [12]. A high Q-factor creates sharp spectral dips in chipless RFID sensors, enhancing sensing precision and resolution. However, a low Q-factor generates broad spectral dips, diminishing sensitivity and accuracy. Similarly, a high Q-factor improves readability and detectability in chipless RFID tags by producing separate spectral signatures. However, a low Q-factor may lead to broader and not-so-clear responses, thereby making identification uncertain. Thus, an optimal balance in the case of chipless RFID sensors and tags is demanded in order to achieve all-around improvement and consistency in all applications. Therefore, this study will further investigate the Q-factor and linear and spherical detectability analysis with the array configurations. However, despite the widespread use of array configurations, the proper theoretical and experimental analysis still needs to be improved to understand the trade-offs between these parameters. Therefore, this paper addresses the identified gaps and proposes solutions. The novel contributions of this paper are as follows:  
1. Experimental validation of the performance of chipless RFID tags using linear and planar array configurations. 2. Examination of detectability highlights trade-offs between tag identification range and angular coverage. 3. Comprehensive analysis elucidates trade-offs among parameters such as linear detectability, spherical detectability, RCS, and Q-factor. 4. Providing guidance for optimising the design and operation of chipless RFID tags based on planar array configurations. The paper is organised as follows: In Section 2, the RCS is introduced, and techniques that can be used for its improvement are discussed. Section 3 presents a link budget analysis of chipless RFID arrays.