# A 2.4 GHz 20 W 8-Channel RF Source Module with Improved Channel Output Balance
## 3 Measurement Results  
The proposed RF source module was implemented in an aluminum body as shown in Figure 9a. The total module size was 244 mm \(\times\) 247.4 mm \(\times\) 30 mm in width, length, and height, respectively. Each part was divided into 5 mm partition walls to prevent interference with between sections. As preparation before the measurement, seven of the eight channels were terminated with attenuators using 50 Ohm termination, and the remaining channel was connected to measurement setup. The measurements were performed by rotating each channel under the same conditions. The measurement setup consisted of E4417A (Keysight Technologies, Santa Rosa, USA) as a power meter, E9323A (Keysight Technologies, Santa Rosa, USA) as a power sensor, E4404B (Keysight Technologies, Santa Rosa, USA) as a spectrum analyzer, N5767A, E36312A, and E3632A (Keysight Technologies) as a DC supply, and Exos-2.5 (Koolance, Auburn, USA) as a liquid circulator. The measurement was performed with the top plate of the module covered, and coolant was circulated at a room temperature of 25 \({}^{\circ}\)C. The details of the measurement results are presented in Figure 9b. As for the output power, it can be confirmed that the target performance was achieved by securing an average of 43 dBm (20 W) for each channel. Moreover, in the previous module, there was a 0.75 dB difference in the output power between channels. In the proposed module, however, the difference of the output power was reduced to 0.18 dB; thus, it was confirmed that the channel output balance was improved. Furthermore, the proposed module has a volume 53.3% lower than that of the previous module.  
Figure 8: Simulation and measurement results of the phase difference between channels: (**a**) in the previous module, (**b**) in the proposed module.  
Figure 7: Photograph of the power dividing part using Wilkinson divider.  
In Table 3, the RF performance of the proposed RF source module is compared with that of the conventional research on plasma generator applications. In the conventional 1-channel application, the module has been manufactured as a pallet amplifier [9; 10] or just a PA test unit [22]. The high-level output power can be presented as an advantage of the conventional 1-channel application, but the output power level of the proposed module can be further increased if it is replaced with a high-power transistor. In contrast, in the conventional multi-channel application, a method that combined several 1-channel modules was presented [4; 5; 23], but only the previous module implemented 8-channel operation by itself [11]. As the conventional modules are implemented by connecting multiple transistors or PA modules, the channel output balance may be different from that of the proposed module; however, the operation of the proposed module can achieve uniformity, high area coverage, and reliability. Further work could improve the module to be stackable to configure more output channels, which would allow it to cover a wider area under stable conditions.  
Figure 9: (a) Photograph of the proposed RF source module with measurement setup; (b) measurement results of each channel.