# A Broadband Ultra High Frequency (UHF) Fat-Dipole Antenna for Digital TV Applications
## 3 Results  
The antenna element was initially tested to assess the influence of the balanced-to-unbalanced conversion. An F-type connector was directly soldered to each of the dipole arms, and the results were later compared to those obtained using an infinite balun. All measurements were conducted in a laboratory environment without shielding or absorbing walls, as an anechoic chamber was not available. Nevertheless, this setup aligns with the intended condition for indoor applications. It is important to note that the measurement results may vary depending on the antenna's position and placement. In addition to laboratory evaluations, virtual simulations allow for antenna verification prior to prototyping, thereby providing confidence during the design phase. To validate this specific case, two different 3D numerical methods were employed using a commercial full-wave electromagnetic field solver. Ideally, these two numerical methods and their respective meshes should yield similar results when analyzing the same structure, demonstrating the consistency of the simulation. The numerical methods used are as follows:  
* CST Microwave Studio transient solver, based on the Finite Integration Technique (FIT) [17]. * CST Microwave Studio frequency domain solver, based on Finite Element Method (FEM) [18]. Figure 9 illustrates the simulation methods alongside the results obtained with the direct connection excitation. It is evident that the results from the two simulation methods vary; however, within the frequency band of interest, the FIT method yielded the best results. Both simulations used a discrete port, which represents an ideal balun with signals 180\({}^{\circ}\) out of phase between its terminals. The difference in simulation results can be attributed to the use of different meshes (tetrahedral for the FEM and hexahedral for the FIT), as well as variations in internal convergence criteria. In the plots, a rectangle delineates the bandwidth of interest. Figure 10 presents a comparison between the two excitation approaches (balun and direct connection), along with the simulation performed using the transient solver of CST Microwave Studio. The balun is constructed by soldering the coaxial inner conductor and the shield to each of the dipoles. The length of the shield section that is soldered is proportional to the wavelength; in this case, approximately 4 cm was used. A realistic 3D simulation of an infinite balun is not feasible because accurately representing the coaxial braided shield requires very fine modeling of the copper mesh, taking into account the holes and gaps in the braided area [19]. Although a section of a coaxial cable was simulated in 3D for electromagnetic compatibility (EMC) purposes, it was performed with a limited length [20]. This geometrical constraint, resulting from the imperfect shielding and the overall length of the cable, leads to a very large aspect ratio with respect to the antenna dimensions. Therefore, the virtual models and the prototype are not rigorously identical due to the presence of the balun. It is evident that the ideal excitation implemented in  
Figure 8: Simulated isolation between the co- and cross-polarizations, for two frequencies, 580 and 700 MHz. The co-component is aligned to the \(\theta\) direction, as the figure shows. the virtual simulation is of paramount importance. Unless a real broadband balun is utilized, additional geometric optimizations are relatively insignificant, as the sensitivity of the prototype connection to the feed cable has a much greater influence on the results compared to minor structural changes. During measurements, it was also observed that common-mode currents flowed in the vector network analyzer cable when touched during direct excitation, generating visible changes in the S11 curve being measured. This indicates a poor conversion between the unbalanced currents from the network analyzer and the balanced termination presented by the antenna.