## 4 Conclusions  
This work introduces a co-design methodology for a microwave amplifier-phase shifter. By integrating the reflection-type phase shifter as the input matching network of the microwave transistor, the optimum source impedance of the microwave transistor matches 50 \(\Omega\) directly. For experimental validation, a standalone conventional microwave amplifier, a conventional reflection-type phase shifter cascaded with a conventional microwave amplifier, and a proposed co-design microwave amplifier-phase shifter were designed,  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**MAs** & **Gain (dB)** & \(P_{\text{M}}\)**(dBm)** & **PSR (\(\cdot\))** & **PDE (\({}^{*}\))** & **Size** \\ \hline CMA & 14.13 & 25.72 & – & – & 0.42 \(\lambda_{0}\times\)0.37 \(\lambda_{0}\) \\ \hline CRTS cascaded with CMA & 13.28 & 24.77 & 195.35 & \(\pm\)6.14 & 1.06 \(\lambda_{0}\times\)0.47 \(\lambda_{0}\) \\ \hline Proposed co-design MA-PS & 13.74 & 25.26 & 185.62 & \(\pm\)4.3 & 0.74 \(\lambda_{0}\times\)0.50 \(\lambda_{0}\) \\ \hline \end{tabular}
\end{table}
Table 4: Electrical performances summary of three fabricated microwave amplifiers above a 200 MHz bandwidth (MA: microwave amplifier; PSR: phase shift range; PDE: phase deviation error; CRTS: conventional reflection-type phase shifter; CMA: conventional microwave amplifier; IMN: input matching network; MA-PS: microwave amplifier–phase shifter).  
Figure 14: Comparison results of three fabricated microwave amplifiers: (**a**) gain and (**b**) \(P_{\text{out}}\) and gain according to \(P_{\text{in}}\) (CMA: conventional microwave amplifier; RTPS: reflection-type phase shifter; CRTS: conventional RTPS; MA: microwave amplifier; CMA: convetional MA; IMN: input matching network).  
fabricated, and their results were compared at \(f_{0}\) of 2.45 GHz. The co-designed structure exhibits a measured gain of 13.74 dB and P1 dB of 25.26 dBm. At 200 MHz, the designed phase shifter achieves a phase shift range of 185.62\({}^{\circ}\) with a phase deviation error of \(\pm\)4.3\({}^{\circ}\). The proposed co-design microwave amplifier-phase shifter not only offers higher gains and better output power performances but it also has a 38.5% smaller size and less design complexity than the typical conventional reflection-type phase shifter cascaded with a conventional microwave amplifier. The proposed topology is effectively suited for the compact and high electrical performances of RF front-end transmitter systems.  
Conceptualization, Y.J.; investigation, P.T.; methodology, Y.J.; supervision, Y.J.; validation, P.T.; writing--original draft, P.T.; writing--review and editing, P.T., P.P. and G.C. All authors have read and agreed to the published version of the manuscript.  
This work was supported in part by the National Research Foundation of Korea (NRF) grant, funded by the Korean Government [Ministry of Science and ICT (MSIT)] (grant number RS-2023-00209081, 40%); in part by the Basic Science Research Program through NRF of Korea funded by the Ministry of Education (under grant RS-2019-NR040079, 40%); and in part by the Institute of Information & Communications Technology Planning & Evaluation (IITP)--Innovative Human Resource Development for Local Intellectualization Program, grant funded by the Korean Government (MSIT) (grant number IITP-2024-RS-2024-00439292, 20%).  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors declare that they have no conflicts of interest to report regarding the present study.