## 4 Experimental Validation  
The photo of the built prototype is presented in Figure 8a. The simulated and measured impedance show good agreement, both operating in the Ka-band as shown in Figure 8c. A  
Figure 7: Simulated 4-by-4 array DLTSA. (**a**) Array design with the proposed DLTSAs with FGM-125. (**b**) Array design with the proposed DLTSAs without FGM-125. (**c**) Reflection coefficients. (**d**) \(\theta\)-sweep radiation patterns (\(\phi=90^{\circ}\)). slightly wider impedance matching at high frequencies and some less-matched points from the measurement are attributed to the fabrication losses and error of the built prototype, respectively. The simulated realized gain of the proposed array antenna with the EM absorber is 14.7 dBi at 35 GHz at \(\theta=\phi=0^{\circ}\) and those for the measured boresight realized gains show 10.1 dBi and 9.8 dBi with and without the FGM-125 absorbers in the proposed array, respectively. The difference according to the presence of the absorber is only 0.3 dB, close to the 0.1 dB difference from the simulation of the single DLTSA. The absolute gain is measured lower than the simulation by 4.6 dB. The deviation might be caused by fabrication errors, especially from the connection loss of the divider to the antenna, which was hardly soldered due to their small dimensions. Other than that, the simulated and measured radiation patterns exhibit overall good agreement as shown in Figure 8d. Furthermore, the radiation patterns in Figure 8e demonstrate that the radiation characteristics are well maintained regardless of the presence of the FGM-125 absorbers, verifying the unique characteristic of the proposed DLTSA expected from the simulations. The null points observed in the back lobe in the measured results are attributed to the CATR environment, which has a jig behind the AUT, as shown in Figure 8b. The RCS is assessed in the X-band. Figure 9 shows the monostatic RCS measurement setup using two standard SGH-90 horn antennas from the MTG corporation and a vector network analyzer (VNA). During the measurement, the two horn antennas are closely positioned, in front of the antenna under test (AUT) aperture as a means of measuring the monostatic RCS. The RCS measurement was carried out indoors using the transmission coefficient method [22; 23; 24]. The indoor measurement setup could be noisy. Therefore, during the measurement, we narrowed the IF bandwidth of the VNA to lower its noise level and obtain more accurate measured results [25]. The distance between the horn antennas and the AUT is denoted as \(R\), and was set to 1.1 m, which is the distance where the AUT can be finely detected considering its electrical dimension. The gain (\(G_{t}\) and \(G_{r}\)) of the horn antenna is 22.1 dBi at 10 GHz [26]. Consequently, the RCS \(\sigma\) can be calculated using (1), where \(P_{r}/P_{t}\) is obtained from \(\left(S_{21}\right)^{2}\) (ports 1 and 2 of the horn antennas) and \(\lambda\) ranges from 36.6 mm to 25 mm [22]. The AUT is rotated by \(90^{\circ}\) for the cross-polarized electric field incidence. \[\sigma=\frac{P_{r}}{P_{t}}*\left[\frac{\left(4\pi\right)^{3}*R^{4}}{G_{t}*G_{ r}*\lambda^{2}}\right] \tag{1}\]  
The RCS values from the simulation and measurement results are presented in Figure 10. As shown in Figure 10a, the cross-polarized monostatic RCS is reduced for the proposed DLTSA with FGM-125 absorbers about 10.6 dB in the X-band. The peak envelope of the measurement results in Figure 10b verify that the RCS is reduced by about 6.5 dB on average in the X-band, and maximally by 14 dB by applying the absorber. The difference between the simulation and measurement might be caused by the non-anechoic chamber environment and the small electrical size of the AUT. The overall RCS is measured lower than the simulation, which is due to the large absorber plane where the AUT is inserted, as shown in the measurement environment photo.