## 4 Results  
The manufactured prototype is shown in Figure 5, while the comparison of the measured and simulated reflection coefficients is presented in Figure 6. The initial results without the microstrip-ESIW transition have been included (denoted as simulated no transition). It can be observed that the measured \(-\)10 dB impedance bandwidth achieves a value of 19%, which is very close to the simulated value of 20%, probably due to a small deviation in _hair_ during welding, as explained before. The difference in the \(S_{11}\) parameter between the simulated and prototype (Figure 6) is due to the presence of the previously mentioned transition from planar to SIC, which produces resonances along the working band due to small impedance mismatches. If we compare the measured results with a simulation of the patch with the microstrip-to-ESIW transition, it can be seen that they are very similar. This confirms that the transition degrades the original response of the patch shown in Figure 6. In an integrated ESIW system, the transition would not be necessary, and the performance with a pure ESIW feed would be recovered. The measured radiation efficiency reaches 90.48% at the central frequency (10 GHz) once the microstrip and connector losses have been removed, closely matching the simulation results. At 9 GHz, this efficiency is 80.77%, and 80.11% at 11 GHz, exceeding 80% efficiency along the bandwidth, again, once the microstrip and connector losses have been removed. To remove these losses, a stand-alone microstrip was manufactured and measured with the same length as that of the feeding line, so that the losses of the feeding can be deduced from the measured S\({}_{21}\) parameter of the line. The radiation characteristics are shown in Figures 7 and 8, showing minimal differences between the simulated and measured results, proving the robustness of the manu  
Figure 6: Measured and simulated \(S_{11}\) of the proposed antenna. The reflection coefficient of the patch without the transition has been included. facturing method. The beam width at \(-3\) dB is around \(40^{\circ}\) for both the XZ and XY cuts. The copolar-to-crosspolar ratio is quite low within the \(-3\) dB beam width, exceeding 20 dB. In Figure 9, the antenna and anechoic chamber can be seen. To compute the gain and measured efficiency, the comparison method was used [25], with the horn antenna _DRH40_ as the reference. In Table 2, a comparison with other similar devices is presented. The proposed ESIW device demonstrates a bandwidth of 19% at a centre frequency of 10 GHz, with a measured radiation efficiency of 90.48% and a directivity of 8.11 dBi. Comparing these results with other devices, the [10] device has less bandwidth and similar radiation efficiency (96%) but higher directivity (9.63 dBi). This antenna uses floating microstrip technology (not a complete integration), so it is not integrated with an ESIW line. This is not significant for a single antenna and a short microstrip feed. However, if this patch is used to develop an array, the microstrip feeding network will introduce more loss than ESIW feeding, and the efficiency of the ESIW integrated array will be notably higher than that of the equivalent array fed with a microstrip. The structure reported in [26] presents a lower bandwidth, efficiency, and directivity, with this antenna being integrated in the microstrip. A single-layer, dual-polarised, high-gain cross-patch microstrip antenna is presented in [27]; it has a lower bandwidth, similar efficiency, and higher directivity. The [14] device shows a lower bandwidth, similar  
Figure 8: Three\(-\)dimensional E\(-\)field radiation pattern simulated (**left**) vs measured (**right**). Figure 7: Normalised radiation farfield cuts at 10 GHz (simulated and measured). efficiency, and lower directivity, using slot integration technology; also, the main difference is that the proposed work has been fully integrated in an ESIW and is fed by a rod, not by a coupled slot.