## 3 Results and Discussions  
The validation test of the sensor ensures that this sensor can be practically used in the frequency range of 0.5-4.0 GHz at 25 \({}^{\circ}\)C to measure the accurate complex relative permittivity, electrical conductivity, and phase constant of material. The measurement test of pure honey can be done by immersing the sensor in pure honey and connecting the other end of the cable to the vector network analyzer and recording the reflection coefficient of the pure honey. In this experiment, three samples with known complex relative permittivity are air (A), distilled water (B), and ethanol (C). Equation (9) is applied to determine the complex relative permittivity of the unknown material. The honey samples are considered the unknown material (UN). The experimental setup is shown in Figure 5.  
The reflection coefficients are used to determine the complex relative permittivity according to Equation (9). Equations (3) and (4) are used to calculate the electrical conductivity and the phase constant. The results of complex relative permittivity both real part and imaginary part, electrical conductivity, and phase constant in the frequency range of 0.5-4.0 GHz are shown in Figure 7. Figure 7a demonstrates the complex relative permittivity in the microwave frequency range of 0.5-4.0 GHz. The complex relative permittivity of pure honey both real part and imaginary part monotonically decreased with increasing  
Figure 6: Sensor validation with (**a**) real part of the complex relative permittivity (**b**) imaginary part of the complex relative permittivity (**c**) electrical conductivity (**d**) phase constant using methanol as an unknown material. frequency. However, in Figure 7b,c, the electrical conductivity, and the phase constant of pure honey increased with increasing frequency. The real part values of complex relative permittivity range between 9.77 and 20.35 while the imaginary part values lie between 5.20 and 10.10. The electrical conductivity values range between 0.28 and 1.12 S/m while the phase constant values lie between 0.05 and 0.26 rad/mm. The real part of the honey sample decreases with increasing frequency (0.5-4.0 GHz), similar to water [23], since the honey sample contains up to 15.90%\(w\)/\(w\) moisture content. The complex relative permittivity, the electrical conductivity, and the phase constant of honey samples in the frequency of 0.5-4.0 GHz are revealed in Figure 7. Further study is performed with water adulteration in honey samples. The sample preparation for the detection of water adulteration in honey can be done by preparing seven different adulterated honey samples as follows: pure honey, honey with water adulteration at 5-30%\(w\)/\(w\). Each adulterated honey sample has five samples to measure for average values. The experiments are performed with the sample temperature of 25 \({}^{\circ}\)C.  
After the measurement, the complex relative permittivity, the electrical conductivity, and the phase constant of the honey samples at different frequencies are calculated and shown in Figures 8-10, respectively. From Figure 8a, when the water content in the honey increases, the real part of the complex relative permittivity increases throughout the 0.5-4.0 GHz frequency range because the real part of the relative permittivity of water is as high as 78.3 [23], results in the real part of the complex relative permittivity of adulterated honey increases as well. Figure 8b shows the imaginary part of complex relative permittivity of the adulterated honey samples with water in the range of 0-30%\(w\)/\(w\). The imaginary part of the complex relative permittivity increases when compared to the pure honey sample. However, each adulterated honey sample with different water content shows slight difference in the imaginary part of complex relative permittivity. The difference of the real part of complex relative permittivity of each honey sample is the highest at lower frequencies.