## 4 Conclusions  
This study addresses the challenges of high loss and bulkiness in MRI RFPA combiners. Leveraging the Wilkinson combiner theory, a novel four-way microstrip capacitor-loaded combiner was designed and fabricated. Through optimization of the microstrip's length and capacitor loading, followed by testing, the combiner achieved an insertion loss reduction of 0.4 dB (30% lower than that of conventional 0.6 dB designs), a power-handling 8 kW peak power, a compact size of 320 \(\times\) 200 \(\times\) 10 mm (30% smaller than its traditional counterparts), a port performance VSWR \(<\) 1.25 (equivalent to a \(-\)25 dB return loss), and isolation \(>\) 30 dB. Finally, the RF combiner was integrated into the RFPA system to achieve the bulk volume, and then imaging experiments were conducted with the 3.0T MRI system; this RFPA combiner demonstrated high efficiency due to lower loss.  
The capacitor-loading technique optimizes the microstrip's electrical parameters, balancing loss and size for high-field MRI systems. Future research directions include scaling to multi-stage combiners for higher-channel MRI systems, adjusting the capacitor-loaded microstrip length Z\({}_{0}\) and structures to make them adaptable to 1.5T-7.0T MRI systems, and microchannel cooling or Low Temperature Co-fire Ceramic (LTCC) processes for 8 kW plus thermal stability. This design methodology can extend to RF ablation and communication systems, advancing high-power RF devices toward miniaturization and low-loss operation.  
Writing--review & editing, Y.L.; Supervision, S.L. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the MRI 3.0T Super Scan Project of Xingaoyi Medical Equipment Co., Ltd., China (No. XGY3T2018001), the Key Project of the Ministry of Science and Technology of China, \"Liquid Helium-free Magnets and Their Integrated Systems\" (No. 2019 YFC0118700), Ningbo Key Research and Development Program (Unveiling and Leading)-Development of a 3T Vertical Brain-Dedicated Innovative Liquid Helium-Free Nuclear Magnetic Resonance Imaging System (No. 2023Z182) and National Key Research and Development Program for Technology-based SMEs-Development of a Liquid Helium-Free Superconducting 3.0T Brain Structure and Function-Dedicated Magnet (No. 2022 YFC2408900). The design was simulated using ANSYS HFSS 2019 R1 for 3D electromagnetic analysis and co-optimized with Keysight ADS 2018; the critical parameters were validated.  
Not applicable.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Combiner Type** & **Insertion Loss (dB)** & **Combining Efficiency** & **Integration Factor** & **Normalized Volume** & **FoM** \\ \hline Microstrip & & & & & \\ Combiner [18] & 0.6 & 87\% (0.87) & 1.2 & 0.44 & 4.0 \\ Lumped- & 0.6 & 87\% (0.87) & 1 & 1 & 1.45 \\ Element [19; 20; 21] & & & & & \\ Magnetic Core & & & & & \\ Transformer [22] & 0.6 & 87\% (0.87) & 1 & 1 & 1.45 \\ This Work & 0.4 & \textgreater{}91\% (0.91) & 1.2 & 0.4 & 6.83 \\ \hline \hline \end{tabular}
\end{table}
Table 11: FoM analysis of this work.  
Data Availability Statement: The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors declare no conflict of interest.