## 3 Results and Discussions
### RF Characteristics of MS lines  
RF components, such as antennas, couplers, and filters, can be formed from MS lines, whereas the resistance of the strip conductors becomes a considerable parameter for laser-scribed MS lines. In this regard, the S-parameters, which quantify how RF signals react with MS lines, were monitored using a vector network analyzer. Moreover, three-dimensional electromagnetic simulations were conducted using CST Studio Suit at a frequency range from 1 GHz to 18 GHz. The parameters for the simulations are according to Table 1.  
The S\({}_{21}\) spectra, which presents the transmission of RF signals through MS lines, is shown in Figure 5. Here, five MS line samples with sheet resistances of 0.25 \(\Omega/\square\), 0.32 \(\Omega/\square\), 0.52 \(\Omega/\square\), 4.61 \(\Omega/\square\), and 186.3 \(\Omega/\square\) were chosen for the simulation and test. The corresponding laser powers were 200 mW, 150 mW, 100 mW, 75 mW, 50 mW, and 37.5 mW, respectively. Figure 5a plots the simulation results. The black dash line shows the idea conditions where the sheet resistance is set as zero. The slightly decrease of S\({}_{21}\) at a frequency below 7 GHz and the wavy shaped curves at higher frequencies are mainly attributed to the impedance discontinuities between the SMA connectors and the MS line. When sheet resistance is below 0.52 \(\Omega/\square\), the S\({}_{21}\) spectra illustrates a similar variation trend to the idea case. The minute differences between curves are partially due to the ohmic losses from the strip conductors that convert electromagnetic waves to Joule heat [13; 14]. Further increasing the sheet resistance to 4.61 \(\Omega/\square\) tremendously reduced the signals transmitted through the MS lines. The S\({}_{21}\) values decreased to around \(-12\) dB, accordingly. Given a more extreme example with a sheet resistance of 183.6 \(\Omega/\square\), the S\({}_{21}\) values dropped well below \(-20\) dB, and even smaller than \(-40\)dB at a frequency below 9 GHz. Note that the presence of resistance can result in an impendence mismatch, whereby the reflection will also reduce the transmit signal lead to a drop of S\({}_{21}\). The reflection will be discussed with the S\({}_{11}\) parameter. The experimental results plotted in Figure 5b are consistent with the simulation results. Compared with the simulations, faster decreases of the S\({}_{21}\) values with an increasing frequency can be attributed to the non-uniformity and discontinuity of the laser-scripted conductors on a micro scale, which increased losses and reflections in higher frequencies. This result also explains the significantly lower S\({}_{21}\) at sheet resistances exceeding 0.52 \(\Omega/\square\). The surface roughness of the samples prepared with a lower laser power is obviously higher than those prepared with a relatively higher laser power. The S\({}_{11}\) spectra illustrates the reflection of RF signals (shown in Figure 6). The periodic curves can be attributed to the discontinuities between the MS line and connectors, which are consisted with the S\({}_{21}\) spectra in Figure 5. The reflection is approximate to the idea of conduction (sheet resistance is zero), with sheet resistances below 0.52 \(\Omega/\square\) for simulations and below 0.32 \(\Omega/\square\) for experiments. On the other hand, the reflection of the signal is more pronounced if we further increase the sheet resistance. S\({}_{11}\) values around \(-10\) dB and above \(-5\) dB were observed when the sheet resistances were 4.61 \(\Omega/\square\) and 183.60 \(\Omega/\square\), respectively. Figure 4: The sheet resistance as a function of laser power.