This paper provides a comprehensive analysis of a complete design of chipless RFID tags on the frequency domain, draw attention to the challenges encountered using two different low-cost flexible substrates at microwave frequencies. The study focuses on present the performance of the L-Bent Dipole and L-Bent Slot at 3.5 GHz to 7.5 GHz frequency band, with resonator’s operation bands designed not to exceed one octave. The implications of this research are especially relevant for future designs of chipless RFID tags, which are highly sensitive to high-loss substrates. The study also provides various models with different codes and highlights the challenges faced during the entire design process.