## 3 Results and Discussion  
Using the configuration described in Section 2.3, the testbed was implemented to test the RABE prototype, obtaining similar results to those from the IC manufacturer's test card AD9364 [12]. Two types of experimental measurements were carried out in order to verify the proper operation of the implemented prototype. In both scenarios, the same settings were used for output power, transmission frequency, and bandwidth parameters. As a result, it was noted that RABE output power (Figure 9a) was reduced by 2 dB compared to FMComMS4 (Figure 9b), which was 7 dB. It is important to mention that according to the AD9364 datasheet, it is able to transmit with a maximum power of 7.5 dBm when matched to 50 ohms load at 2.4 GHz. Based on the Nyquist noiseless channel, the theoretical maximum bit rate is defined as equal to twice the bandwidth symbol (BW) per second. If each symbol can carry M different distinguishable levels, then each pulse carries log M bits of information, which is described by  
\[\mathbf{C}=2\text{BW }\text{log}_{2}(M)\quad\text{bits/sec} \tag{1}\]  
Since the bandwidth of the AD9364 ranges from 200 KHz to 56 MHz, the data rate capacity for quaternary modulation, \(M=4\), will be between 0.800 and 224 Mbps. Figure 8: Testbed block diagram. Configuration for the connection of the test bed for the prototype. In Figure 10, the graph of the data collected in the test bench shows the spectrum transmitted by a signal with a carrier frequency of 2.6095 GHz to verify the correct operation of the design in different frequencies. The spikes shown at 2591 and 2599, are unidentified carriers external to the prototype system. The output power available at the carrier frequency in Figure 10 was \(-\)20 dBm, as shown. A Gaussian 3 dB resolution bandwidth (RBW) filter was applied into the signal analyzer followed by a Fast Fourier Transform (FFT) with a BW of 411.9 kHz. The BBP was set in a QAM modulation scheme at the testbed (as shown in Figure 11). The resulting modulation process was controlled and synchronized by the BBP to the RABE stage via the FMC connector. The Total Harmonic Distortion (THD) percentage was measured as described in [17] and is given by  
\[\mathrm{THD}_{n}=\sqrt{\frac{\sum_{n=2}^{\infty}Po_{n}}{Po_{1}}}\times 100, \tag{2}\]  
where \(Po_{n}\) is the output power of the n-th harmonic in watts, and \(Po_{1}\) is the output power of the fundamental frequency in watts. Figure 10: Spectrum of signal transmitted at 2.6095 GHz. Further processing of the data shows the spectrum of the carrier signal transmitted at 2.6095 GHz. Figure 9: Implementation of the test bed for the RABE prototype. (**a**) tests of the manufactured prototype. (**b**) tests of the FMCOMMS4 card. According to measurements made in the Lab using the N9030A Signal Analyzer, for \(n=10\) harmonics, as shown in Table 4, it was found that  
\[\mathrm{THD}_{n}=3.81\%.\]  
The distortion values due to the harmonics generated by the transmitter stage could reach values of up to 3.8%, reducing the output power of the RF signal, as shown in Table 4.  
Communication systems with a low THD produce less interference between electronic devices connected to or close to the PCB. In Figure 12, the spectrum generated by the RABE is shown, which was taken directly from the RF output by the N9030A analyzer, all this at a frequency centered at 2.300 GHz, in which it is allowed by the Mexican government for experimental satellite links according to the frequency allocation table [18]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Harmonic** & **Frequency (GHz)** & **Value (dBm)** \\ \hline
1 & 2.30 & \(-12.01\) \\
2 & 4.60 & \(-40.4\) \\
3 & 6.90 & \(-72.25\) \\
4 & 9.20 & \(-81.3\) \\
5 & 11.50 & \(-80.9\) \\
6 & 13.80 & \(-79.9\) \\
7 & 16.10 & \(-79.7\) \\
8 & 18.40 & \(-76.9\) \\
9 & 20.70 & \(-75.11\) \\
10 & 23.00 & \(-74.32\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Harmonics generated by the RABE at 2.30 GHz. Figure 11: Signal analyzer, RABE and Zedboard on QPSK.