## 4 Experimental Results
### Measurements with Modulated Signal  
In order to verify the proposed integrated mmWave power amplifier in a real signal environment, we measured the error vector magnitude (EVM), adjacent channel leakage ratio (ACLR), average input and output channel power and PAE using a 100 MHz 16-QAM 3 GPP/NR OFDM signal. A 16-QAM modulation scheme was selected so that EVM and ACPR limits would occur around the same output power range. With 64-QAM and 256-QAM, the EVM limits would have been at a lower output power compared with the more relaxed ACPR limit (see Tables 1 and 2). The measurement setup is explained in Section 3. The reference measurement at the center of the 3 GPP/NR FR2 band n258--i.e., 26 GHz--including cables, probes and the on-chip Thru standard is presented in Figure 10. The loss of the complete measurement path was 7.2 dB with the reference EVM level of 1.63 %. Figure 9: Measured figure of merits vs. frequency. (**a**) Pout, (**b**) PAE and (**c**) gain with I\({}_{\text{QQ}}\) = 17.7 mA (solid line) and I\({}_{\text{QQ}}\) = 48.7 mA (dashed line). The losses of the input and output paths to the reference planes, shown in Figure 5, were 2.5 dB and 4.7 dB, respectively. The measurement results at the center of band n258--i.e., 26 GHz--are shown in Figure 11 and at the lower edge of the band at 24 GHz in Figure 12, where single-tone measurements showed the highest PAE and output power. Results are shown with three different \(\mathrm{I_{4Q}}\) values: \(\mathrm{I_{4Q}}=17.7\) mA (minimum bias, red curves), \(\mathrm{I_{4Q}}=36.7\) mA (medium bias, blue curves) and \(\mathrm{I_{4Q}}=48.7\) mA (maximum bias, black curves). The measured results are plotted in Figures 11 and 12 as a function of average output channel power. PAE and EVM are plotted in the same subfigure and ACLR upper and lower in another subfigure. Figures also include the EVM and ACRL specifications (see Tables 1 and 2), which for the used signal were 12.5 % and \(-\)28 dBc, respectively. The EVM results at the center of the band n258 (Figure 11a) show that the black and blue curves were similar. On the other hand, the EVM with the minimum bias current was above 5 % at lower average channel power levels but matched with others above the average output channel power of 13 dBm where the EVM = 8 %. The specified EVM limit 12.5 % was achieved at 14.5 dBm average channel power regardless of the bias current. This was a very good result considering that the measured 1 dB compression point at 26 GHz was around 17.5 dBm. The specified ACLR limit \(-\)28 dBc (see Figure 11b) was achieved with the minimum bias current (red lines) at an average channel power of 13.5 dBm while the EVM = 9 %. With medium and maximum bias currents, the ACLR increased linearly, overlapped and showed good symmetry. With the minimum bias current (\(\mathrm{I_{4Q}}=17.7\) mA), one can clearly see the asymmetry and higher distortion at lower drive levels. Interestingly,  
Figure 11: (**a**) EVM, PAE and (**b**) ACLR as a function of average output channel power at three different bias currents at 26 GHz using 100 MHz 16-QAM 3 GPP/NR2 OFDM signal. Figure 10: Reference measurement of the test systems at 26 GHz using 100 MHz 16-QAM 3 GPP/NR OFDM signal. there seems to be a sweet spot for the IMD before a rapid increase in ACLR takes place and the ACLR levels of the higher bias are reached. At the lower end of band n258 (24 GHz in Figure 12), a similar behavior can be seen in terms of EVM. However, at 24 GHz, asymmetry can be seen in each bias current. Thus, the specified \(-\)28 dBc limit was met only up to 12 dBm of average output channel power with the higher bias setting and 13 dBm with the lowest bias setting. The PAE results shown in Figure 11a are different from the EVM and ACLR results. For instance, at the specified EVM of 12.5%, the average output channel power was 14.5 dBm, which was the same for each bias current, but with \(\text{I}_{\text{QQ}}=48.7\) mA PAE = 12%, which was a good result. However, with \(\text{I}_{\text{QQ}}=17.7\) mA bias current, the PAE was as high as 16%.