## 3 Results  
### Reflection Coefficient  
The reflection coefficient of the four types of glass antennas (case 1-4) was measured by using Agilent N5230A Vector Network Analyzer (VNA) (Agilent Technologies, CA, USA). The calibration kit 3.5 mm Agilent 85052D was used for VNA calibration of both ports before measurement. The measurement setup for antenna reflection coefficient was depicted in Figure 5. The reflection coefficients of the antennas when connecting with port one and port two were tested in order to verify calibration property and reduce measurement error. Figure 6 presents the measured reflection coefficients and the corresponding simulation result. Note that all simulations of these antennas in four cases are set as follows: The boundary settings of both radiator and ground plane are ideal conductive surfaces, and the sweep range is 6-10 GHz with a step size of 0.01 GHz. Table 3 summarizes the measured and simulated results with more detail, including the resonant frequencies, the corresponding reflection coefficients and the \(-\)10 dB bandwidths of these four cases. As observed from Table 3 and Figure 6a, the measurements of the case one antenna with CCF as the radiator and ground plane are in a good agreement with the simulation. However, the resonant frequencies of case two and case three antennas are 9.2 GHz and 11.1 GHz, with a frequency shift of 1.2 GHz (15%) and 3.1 GHz (39%), respectively, when compared with the simulated resonant frequency (8 GHz). For the case four antenna composed of CSP as the radiator and ground plane, it has two resonant frequencies at 7.15 GHz and 9.43 GHz, as shown in Figure 6d, with 0.85 GHz (11%) and 1.43 (18%) offset. For the structures of case 1-3 antennas, case two and case three are equivalent to replacing the radiator and ground plane of CCF layer in case one with ITO material, respectively. Combining the measured reflection coefficients of case two and case three antennas for analysis, the case two antenna has a smaller frequency shift, but the magnitude of the reflection coefficient at the resonant frequency for case three antenna is closer to the simulated one. Although ITO films have the advantage of highlight transmission, the best resistivity available in literature might only reach 0.4 \(\times\) 10\({}^{-3}\)\(\Omega\)\(\times\) cm [25], which is too large when comparing with metallic copper material. Therefore, the high resistivity of ITO films has an impact on the magnitude of reflection coefficients. In addition, one study presented by [PERSON] et al. implies that the semiconductor property of ITO films may affect the effective dielectric constant of the fabricated antenna [26], resulting in a shift of resonant frequency. The case two antenna uses ITO film as the radiator, and due to the aforementioned high resistivity and semiconductor property of ITO films [27], there is a frequency shift for the resonance point, and the corresponding magnitude of reflection coefficient is larger than the simulated results. A similar reason is also applicable for explaining the measured reflection coefficient of the case three antenna. While since the ground plane in case three antenna is an ITO film, the measured reflection coefficient of the case three antenna is different from that of the case 2 antenna. Figure 5: The measurement setup for antenna reflection coefficients. CSP material was employed for both the radiator and ground plane of the case four antenna, for which its electrical conductivity is between CCF and ITO film. We also investigated the cause of resonance shift in the case four antenna by analyzing fabrication and processing sizes. Finally, we found that the actual size of the rectangular patch width of case four antenna is 7.58 mm, which is much larger than the designed value of 7.10 mm. Figure 7 depicts the microscopic images of the radiation patch edges of the case one antenna and case four antenna, which are manipulated by laser etching technology and printing technology, respectively.