# A Broadband Analog Predistortion Linearizer Based on GaAs MMIC for Ka-Band TWTAs
## 6 Conclusions  
In this paper, a Ka-band broadband APD MMIC with an area of 1.6 mm \(\times\) 2.0 mm is proposed based on the 0.15 \(\upmu\)m GaAs pHEMT process. The APD circuit has independent gain and phase adjustment capabilities, which is suitable for the nonlinear compensation of multiple TWFAs with inconsistent nonlinearities. The independent tuning performance of gain and phase conversion improves the compensation accuracy effectively. Meanwhile, the APD MMIC achieves broadband phase matching with a TWTA in the operating bandwidth of 25.1-27.5 GHz through the addition of the NFAM. When the APD MMIC is  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Reference**} & **Operating** & **Signal** & **C/IM3 or ACPR** & **Independently** & **Co-Design** & \multirow{2}{*}{**Size**} & **Technique** \\  & **Band** & **Bandwidth** & **Improvement** & **Tunable** & & **with PA** & \\ \hline
[12] & 29-31 GHz & N/A &
\begin{tabular}{c} 903 dB \\ OPBO(C/IM3) \\ \end{tabular} & Yes & No & \(28.5\times 31.4\) mm\({}^{2}\) & HMIC \({}^{2}\) \\ \hline
[13] & 5.5–5.8 GHz & N/A &
\begin{tabular}{c} 1383 dB \\ OPBO(C/IM3) \\ \end{tabular} & Yes & No & N/A & HMIC \\ \hline
[16] & 3.4–3.6 GHz & 55 MHz &
\begin{tabular}{c} 8.406 dB \\ OPBO(ACPR \({}^{1}\)) \\ \end{tabular} & Yes & No & N/A & HMIC \\ \hline
[19] & 40–50 GHz & 1 MHz &
\begin{tabular}{c} 803 dB \\ OPBO(ACPR) \\ \end{tabular} & No & Yes & \(2.0\times 1.0\) mm\({}^{2}\) & MMIC \\ \hline
[22] & DC-90 GHz & N/A & \
\begin{tabular}{c} 903 dB \\ OPBO(C/IM3) \\ \end{tabular} & No & Yes & \(1.6\times 0.7\) mm\({}^{2}\) & MMIC \\ \hline This work & 25.1–27.5 GHz & 500 MHz &
\begin{tabular}{c} 1003 dB \\ OPBO(C/IM3) \\ \end{tabular} & Yes & No & \(2.0\times 1.6\) mm\({}^{2}\) & MMIC \\ \hline \hline \end{tabular}  
\({}^{1}\) ACPR refers to the adjacent channel power ratio. \({}^{2}\) HMIC refers to the hybrid microwave integrated circuit.  
\end{table}
Table 2: Comparison with similar APD linearizers.  
combined with a Ka-band TWTA, the gain compression is reduced from 7 dB to 3 dB and the phase compression is reduced from 40\({}^{\circ}\) to 12\({}^{\circ}\). When OPBO = 3 dB, the C/IM3 is better than 28 dB over the whole operating band and the NPR remains basically steady and better than 15.7 dBc as the signal bandwidth increases from 100 MHz to 500 MHz, which shows that the APD circuit can improve the nonlinearity of broadband TWTAs effectively. This type of APD circuit has high consistency in batch production. Moreover, due to its small size and monolithic design, it is very suitable for integration with other microwave circuits in the front-end of TWTAs to form an APD microwave module with complex and diverse functions.  
Conceptualization, T.L., X.S. and G.W.; methodology, T.L., X.S. and G.W.; software, T.L. and R.F.; validation, T.L., R.F. and D.Z.; formal analysis, T.L.; investigation, T.L. and B.Z.; resources, T.L. and D.Z.; data curation, T.L.; writing--original draft preparation, T.L.; writing--review and editing, B.Z., X.S. and G.W.; visualization, T.L.; supervision, T.L.; project administration, T.L.; funding acquisition, T.L. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.