## 4 Polar-Mode Wideband VHF PA Demonstrator Results  
The combination of the SEPS, WLEA, and VHF class-D PA was carried out, as shown in Figure 15, where all the implemented circuits can be seen, and their main elements are identified. In this assembly, special attention was paid to the connection between the output of the WLEA and the power port of the class-D PA. This should be as short as possible, since large bandwidth signals are handled by these circuits, and the increase in inductance at this point may contribute to a deformation of the amplified envelope waveform. Figure 14: Time-domain measured EA output (\(v_{SE}\)) and SEPS output (\(v_{E}\)) for the envelope of the 4C-CH VDL-T signal at 125 W peak output power: (**a**) envelope waveforms (\(v_{SE}\) and \(v_{E}\)) and (**b**) detail of the EA output (\(v_{E}\)) waveform. Figure 13: SEPS slow envelope DPWM (\(\tau_{PWM}\)) control signal spectra for the envelope of the 4C-CH VDL-T signal together with the frequency response of the SEPS low-pass filter magnitude. To verify the viability of the polar amplification system developed in this work, the test bench shown in Figure 16 was employed. All the test and measurement instruments used are described in Figure 16, and a PC running MATLAB was used for the control of these instruments and for the generation, capture, and processing of the signals used in the tests that were carried out. These measurements include tests of multicarrier signals with analog and digital modulations. The signals were generated using MATLAB, and the constant envelope-phase modulated signal was loaded into the vector signal generator (Agilent E4438C), using a sampling rate of \(f_{\mathrm{s}}\) = 100 MHz, while the envelope signal and the PWM of the slow envelope were transferred to the arbitrary waveform generator (Agilent 81150A), with a resulting sampling frequency of approximately \(f_{\mathrm{s}}\) = 50 MHz. In the first case, the results shown in Figure 17a correspond to the 2C-CH AM-T signal with a carrier spacing of 5 MHz (at 125 MHz center frequency). In the second test, the carriers of the 2C-CH AM-T signal were separated up to 10 MHz to determine the limits of the demonstrator, as shown in Figure 17b. The AM test ends with a 4C-CH AM-T signal (located at 120 MHz, 123 MHz, 128 MHz, and 130 MHz), which can be seen in Figure 17c. This test covers a total bandwidth of 10 MHz, with more than 40 dB of attenuation for the unwanted spectral components, and presents good linearity figures for each individual channel, as seen in the detail of one of the channels shown in Figure 17d. The main supply voltage used to take these measurements was \(V_{S}\) = 34 V, the peak output power reached \(P_{OUT}\) = 94 W PEP, and the resulting overall power efficiency was \(\eta_{O}\) = 47%. This can be considered a satisfactory figure considering that the signal used in the test has a PAPR = 6.5 dB and taking into account the PSD of the signal envelope. Figure 15: Demonstrator circuit of the SEPS, WLEA and class-D VHF PA polar-mode assembly. Figure 16: Test bench used to take the measurements of the implemented polar-mode VHF PA demonstrator. Figure 17: Spectral measurements of AM-T multicarrier signals at the output of the polar-mode PA at 94 W peak output power (RF PA \(I_{Q}\) = 2 A; and main supply voltage, \(V_{S}\) = 34 V): (**a**) 2C-CH AM-T signal 5 MHz carrier spacing, (**b**) 2C-CH AM-T signal 10 MHz carrier spacing, (**c**) 4C-CH AM-T signal 10 MHz bandwidth, and (**d**) detail of the 123 MHz channel. The second set of measurements was carried out using the 4C-CH VDL-T signal (located at 120 MHz, 123 MHz, 128 MHz, and 130 MHz). The metrics used to determine the performance that can be obtained in this case, were the adjacent channel power ratio (ACPR) and error vector magnitude (EVM) for each channel, the measurement of spurious in the operating band, and the total power efficiency of the polar amplifier.