# Reconfigurable Diplexer-Based Filtenna for Tx/Rx Operation in Mobile Satellite Terminals
## 4 Results and Discussion  
The projected reconfigurable filtenna was manufactured, and the prototype is shown in Figure 10. In this section, the antenna is characterized in terms of its main properties, for both operating bands (20 GHz and 29 GHz), through simulation and measurements results. Port 1 was used for the downlink band and port 2 was used for the uplink band. The filter structures combined in the antenna feeding network, as presented in Figure 11, were simulated to analyze the losses of the structure, and the results are shown in Figure 12.  
Figure 10: Photography of the fabricated filtenna prototype. Figure 9: Complete structure of the designed reconfigurable filtenna (dual-band antenna and feeding arrangement with filters). Figure 12 shows the attenuation of the signals (in both bands 20 GHz and 29 GHz) in the feeding structure (filters and microstrip lines). It is possible to observe that the uplink signal suffers an attenuation of 4.6 dB until it reaches the antenna and the downlink signal suffers an attenuation of 1.5 dB until it reaches port 1. Figure 13 presents the comparison between the simulated and measured reflection coefficient in port 2, in the transmission mode (operating at 29 GHz). Analyzing Figure 13, it is possible to observe a similar behavior of both simulated and measured curves, despite a slight deviation in the central resonance frequency. Regarding the simulation results, it can be concluded that the filtenna is properly adapted with a reflection coefficient of \(-\)21.3 dB at 29 GHz. The simulated bandwidth is 1.58 GHz (28.35-29.93 GHz). In terms of the measured results, the antenna at 28.55 GHz has an S\({}_{22}\) of \(-\)15 dB with a bandwidth of 1.1 GHz (27.85-28.95 GHz). The main discrepancies could be explained by possible inaccuracies in the manufacturing process, due to the small dimensions of the structure. Figure 11: Structure of antenna feeding using filters. Figure 12: Simulated losses of the filtenna feeding structure. Figure 13: Simulated and measured reflection coefficient of the filtenna in transmission mode. In Figure 14, the simulated and measured normalized radiation patterns are shown for the two main radiation planes, at 29 GHz. It is possible to see an adequate correspondence between both curves. The simulated gain was 7.41 dBi, and the measured gain was 4.61 dBi. Some deviations can be explained by the impact of connectors and the DC wires in the radiation. When the PIN diode is forward-biased, the filtenna changes the operation frequency band to 20 GHz for the receiving mode. In such case, the comparison between the simulated and measured S\({}_{11}\) is shown is Figure 15.  
According to Figure 15, the simulated S\({}_{11}\) is \(-42.4\) dB at 20 GHz, and its measured value is \(-21.3\) dB (also at 20 GHz) with a bandwidth of 2.55 GHz (18.8-21.35 GHz), assuming the commonly used criteria of S\({}_{11}<-10\) dB. Figure 16 shows the comparison between the simulated and measured radiation patterns for both planes, at 20 GHz. It is possible to notice an identical performance in both curves. The simulated gain was 5.62 dBi, and the maximum measured gain was 4.01 dBi. An important measure in a two port system, such as this designed structure, is the isolation between the two ports, as provided in Figure 17, which reflects the level of effect that a signal on one port has on the opposite port. Figure 14: Radiation pattern to 29 GHz, (**a**) Plane \(\varphi\) = 90\({}^{\circ}\) and (**b**) Plane \(\varphi\) = 0\({}^{\circ}\). Figure 15: Simulated and measured reflection coefficient of the filtenna to 20 GHz. When the PIN diode is ON and the antenna is in receiving mode (at 20 GHz), it is possible to conclude that the simulated and measured values are similar, and the isolation is higher than 30 dB at 20 GHz, and it is always above 25 dB in the evaluated band. These results were expected since the downlink signal should be sent all the way to port 1.