## 4 Measurement and Comparison of Related Antenna  
Figure 14 depicts the fabrication and comparison of measurement and simulation results for ESEPT-CVA and MLPT-CVA. At 4 GHz, both antennas have a greater gain than the RPT-CVA, as seen in Figure 7. Antenna measurements are carried out by taking \(S_{11}\) antenna data using a brand VNA Siglent which works from a frequency of 100 kHz to 3.2 GHz. From the measurement results, it is found that the \(S_{11}\) antenna measured by VNA produces better results at low frequencies. It is known that the measurement results are in agreement with the simulation results where most of the antennas have \(S_{11}\) below \(-10\) dB. High-gain antennas can be applied to radar applications. The Vector Network Analyzer is a tool that can use for measuring radio frequency scattering properties in radar applications. When two ports of the VNA are linked to the antenna, the \(S_{21}\) data can explain the transfer function of the signals emitted and received as shown in Equations (4) and (5). \(S_{x}(t)\) represents the chirp signal with a certain period and bandwidth, whereas \(S_{y}(t)\) represents the received signal chirp [49]. \[S_{y}(f)=S_{21}S_{x}(f) \tag{4}\]  
\[S_{r}(t)=F^{-1}S_{y}(f) \tag{5}\]  
In this study, we used an antenna to detect objects behind the wall. The antenna used is MLPT by connecting it to a portable nano VNA that works at a frequency of 0.5-3 GHz. The antenna and the detected object are varied in distance to the wall. The detected object is a laptop varying the object's distance from the wall and the detection process is carried out by placing the antenna on the E-plane. The antenna is connected to the VNA and the VNA is connected to the laptop. The Scattering signal received will be seen on the laptop display as shown in Figure 15.  
The detected wall has an area of 60 \(\times\) 150 cm\({}^{2}\) by dividing the area into several segments area in the \(x\) and \(y\) direction. The \(S_{21}\) data received on the laptop will be processed and a signal reconstruction process will be carried out so that object detection results are produced as shown in Figure 16. The yellow circle shows the position of the detected target in the x-y plane. Figure 14: Simulation and measurement result of (a) ESEPT-CVA and (b) MLPT-CVA. Table 2 reveals that there has been some research on Vivaldi antennas that operate at low frequencies, but they have not taken into account mutual coupling. In this case, we also compare the antenna element. As shown in Table 2, Our antenna has a smaller width than the antenna at [50]. It employs ceramic materials to operate at a frequency of 0.5 to 3 GHz. The antenna has a wide bandwidth of 0.5-6 GHz has been discussed in [51]. That antenna achieves a gain of 8 dBi at a frequency of 2 GHz, but as frequency increased, the gain declined. A big CVA antenna, which operated at a very low frequency has been evaluated in [52]. However, the maximum frequency used in research [53; 54] is 2.1 GHz. The AVA antenna for GPR application with metamaterial and DGS structure has been discussed in [55; 56] with a larger size than our purposes study. Aspects of our research operate between 0.5 and 4.5 GHz. The ESEPT-CVA and MLPT-CVA antennas, with  
Figure 16: Radar target detection in the xy-planes. Figure 15: Radar target measurement with MLPT-CVA prototype. respective elemental gains of 9.7 dBi and 13.4 dBi at 4 GHz, are used in this comparison. In this study, ESEPT-CVA and MLPT-CVA were arranged in MIMO \(1\times 2\) to produce 12.87 dBi and 16.561 dBi gains at 4 GHz frequency. The comparative performance of 15 Vivaldi antennas is displayed in Table 3 to get the performance in \(1\times 2\) Palm Tree MIMO antenna. Table 3 shows that the best \(S_{11}\) at the 0.5 GHz frequency was obtained by ESEPT which is \(-16.86\) dB, but for the overall working frequency included in \(S_{11}\) less than \(-10\) dB is BCPT as shown in Figure 3b. Table 3 also shows that the best S21 at the 0.5 GHz frequency was obtained by HWSPT which was \(-18.57\) dB.