## 3 Experimental Results  
Figure 17 shows the fabricated antenna and its measured performances in the P-band. An antenna without the metamaterial absorber was also fabricated for comparison. The far-field radiation performance at 580 MHz was measured in an anechoic chamber. Figure 17d,f show the simulated and measured performances (reflection coefficient, isolation) of the proposed antenna with and without absorber. As shown in Figure 17d,f, the measured \(-10\) dB reflection coefficient bands cover the target band, regardless of the presence of the absorber; however, the measured isolation characteristics are changed due to the absorber. Without the absorber, the measured isolation characteristics between the Tx and Rx antennas are lower than 20 dB over the target band. On the other hand, with the absorber, the measured isolation characteristics are higher than 20 dB over the target band. Figure 17b shows the simulated and measured radiation patterns at 580 MHz with the absorber. Measurements were performed when Port 1 was excited. The simulated and measured  
Figure 16: Proposed antenna: (**a**) geometry of proposed antenna, (**b**) simulated S-parameters of P-band, and (**c**) simulated radiation patterns at 580 MHz when Port 1 is excited.  
\begin{table}
\begin{tabular}{c c c} \hline
**Structure** & \(\mathbf{-10}\) **dB Reflection Coefficient Band** & **Isolation (\(\mathbf{1S_{MN}}\)) in Target Band** \\ \hline Without metamaterial absorber & 433.81–796.3 MHz & \(\mathbf{|S_{MN}|}\)\(\mathbf{|<19.2}\) dB \\ With metamaterial absorber & 311.26–838.12 MHz & \(\mathbf{|S_{MN}|}\)\(\mathbf{|>23.44}\) dB \\ \hline \end{tabular}
\end{table}
Table 5: Simulated S-parameter performances of the proposed antenna with and without metamaterial absorber.  
radiation gains at \(\theta=0^{\circ}\) were 1.83 and 1.36 dBi, respectively. Discrepancies between the simulated and measured results may be caused by fabrication and measurement errors, such as slight misalignment between the reference antenna and the fabricated antenna.  
Figure 18 shows the measured performances of the fabricated antenna in the Ka-band. As shown in Figure 18a, the measured \(-10\) dB reflection coefficient bands fully cover the target band. Isolation characteristics between the Tx and Rx Ka-band antennas were measured, as shown in Figure 18b. Simulation could not be performed, because the proposed antenna structure is electrically large at 35 GHz. The distance between the Tx and Rx patch antenna arrays is 208 mm (\(\approx\)24.26 \(\lambda_{0}\) at 35 GHz), which is sufficient to allow for high isolation characteristics. According to the measured results, isolation characteristics of more than 60 dB over the target band were achieved. Figure 18c shows the simulated and measured radiation patterns at 35 GHz when Port 5 is excited. The simulated and measured radiation gains were 10.25 and 8.49 dBi, respectively. The simulated FBR was  
Figure 17: Fabricated antenna: (**a**) photographs of fabricated antenna, (**b**) simulated and measured radiation patterns at 580 MHz with absorber (when Port 1 is excited), (**c**) measurement setup of fabricated antenna without absorber, (**d**) simulated and measured performances (reflection coefficient, isolation) of the proposed antenna without absorber, (**e**) measurement setup of fabricated antenna with absorber, and (**f**) simulated and measured performances (reflection coefficient, isolation) of the proposed antenna with absorber.  
13.23 dB, although FBR measurements could not be performed due to the limitations of the rotating angle at the measurement facility.