## 4 Experimental Results  
Once the simulations had demonstrated the feasibility of the presented structure, the proposed antenna system was manufactured for its validation, and its performance was examined. The fabricated components of the DM-CHA system, including the DMC and  
Figure 8: E-field simulation of the Dual-Mode Conical Horn Antenna (DM-CHA). (**a**) Excitation by the \(TE_{10}{}^{rec}\) mode of port 1, generating the sum (\(\Sigma\)) radiation pattern. (**b**) Excitation by the \(TE_{10}{}^{rec}\) mode of port 2, generating the difference (\(\Delta\)) radiation pattern. Figure 9: Simulated reflection coefficient for the \(TE_{10}{}^{rec}\) mode: in the \(TE_{10}{}^{rec}\)-\(TE_{11}{}^{cir}\) and \(TE_{10}{}^{rec}\)-\(TE_{01}{}^{cir}\) mode converters working independently; in the Dual-Mode Converter (DMC); and in the Dual-Mode Conical Horn Antenna (DM-CHA). the isolated CHA, are shown in Figure 10. The port names follow the same criteria used in Figures 7 and 8. Subtractive manufacturing by Computer Numerical Control (CNC) was used to fabricate the DMC. This minimized possible fabrication asymmetries that would result in high-order mode excitation. Additive Manufacturing (AM) by Direct Metal Laser Sintering (DMLS) was used to fabricate the CHA, with a post-processing treatment of sandblasting to reduce the roughness of the metal powder. The DMC network is made up of two parts. The lower part contains two standard WR-28 rectangular waveguide flanges (_port_ 1 for the sum \(\Sigma\) pattern and _port_ 2 for the difference \(\Delta\) pattern) and the mode converters. The upper part serves as a cap to cover the feeding network. It also includes a small part of _port_ 2 to complete it. The measurement setup of the integrated DM-CHA system, which is connected to a two-port Vector Network Analyzer (VNA - Anritsu model MS46122B-040), is presented in Figure 11a. The S-parameters were measured and a comparative study was carried out between the simulated and measured results in Figure 11b. The return losses for the \(S_{11}\) (sum \(\Sigma\) pattern) and \(S_{22}\) (difference \(\Delta\) pattern) are better than 20 dB and 9 dB, respectively, in the frequency range of 37.5 to 39 GHz. This shows a good agreement with the simulated results. Likewise, the measured isolations \(S_{12}\), \(S_{21}\) are better than 35 dB across the whole bandwidth, providing a satisfactory level of isolation between both the sum and difference ports. It should be noted that the simulated \(S_{12}\), \(S_{21}\), with perfect symmetries, are below \(-70\) dB. Figure 11: Dual-Mode Conical Horn Antenna (DM-CHA). (**a**) Measurement setup. (**b**) Measured and simulated S-parameters of the DM-CHA system. Figure 10: Manufacturing scheme of the Dual-Mode Conical Horn Antenna (DM-CHA). It includes the Dual-Mode Converter (DMC) and the Conical Horn Antenna (CHA). In the next step, the measurement setup in the anechoic chamber of Escuela Politecnica Superior of Universidad Autonoma de Madrid [61] is presented in Figure 12 to analyze the radiation patterns. Both sum (\(\Sigma\)) and difference (\(\Delta\)) radiation patterns were generated by exciting subsequently their associated nominal WR-28 standard rectangular waveguide ports in the frequency bandwidth of 37.5-39 GHz. A waveguide matched load was connected to the port associated to the non-measured pattern. The purity of the two modes generated by the DMC and their interaction with the CHA were checked, comparing them with the simulations for the radiation of the DM-CHA in Figure 8. Figure 13 shows the simulation and measurement results of the normalized radiation pattern in azimuth plane (\(\varnothing=0^{\lx@math@degree}\), according to the coordinate system presented in Figure 8), at the three selected frequencies of 37.5, 38, and 38.5 GHz.