## 5 Discussion  
From the performance summary in Table 3, it is evident that the output power of current dual-band or multi-band power amplifiers is generally insufficient (below 26 dBm). Furthermore, when the distance between high and low frequency bands is significant, both the output power and efficiency in the higher frequency bands tend to decrease. However, the saturated output power of the proposed dual-band power amplifier, achieved using the design methodology proposed in this paper based on the insertion loss optimization of matching networks, is significantly higher than that of current power amplifiers of the same type. Moreover, its efficiency does not show notable degradation, which validates the correctness of the proposed design methodology. This paper addresses the issue of insufficient output power commonly found in current dual-band and multi-band power amplifiers.  
In terms of topologies of PAs, both this paper and references [17, 28, 29, 30] employ a linear power amplifier topology biased in Class A or Class AB. In contrast, reference [31] uses a switching power amplifier biased in Class E, which offers a significant efficiency advantage over linear power amplifiers. In terms of occupied area, references [17, 29]  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **This Work *** & [17] ** & [28] ** & [29] ** & [30] ** & [31] ** \\ \hline Freq (GHz) & **2.4/4.9–5.9** & 2.4/5–6 & 2.4/ 4.9–5.9 & 2.5/3/3.5 & 1.8/2.6 & 2.4/5 \\ \hline Bandwidth & **2.06–3.04/3.15–6.6** & 2.1–2.8/4–6 * & 2.2–3.2/3.8–6.5 * & 2.2–2.8/2.8–3.6/3.1–4.1 * & N. A & 2–5 * \\ \hline Gain (dB) & **9.45/11.48–10.03** & 14/18–16 & 9.2/11.3–11.9 & \(\sim\)15 & 10–11 * & 12.3/8.4 \\ \hline \(P_{sat}\) (dBm) & **28.03/27.5–28.2** & 25.4/24.4–24.8 & 23/21.9–22.4 & 22.5/21.5 & 26.2/23.1 & 21.5/21.4 \\ \hline PAE (\%) & **33.25/24.6–31.1** & 25/20.8–27.3 & 27/24.2–28.2 & 16.5/15(DE) & 32.2/31.8 & 38.4/31 \\ \hline VDD (V) & **3.3** & 2.5 & 2.5 & 1.2 & 3.3 & 3.6 \\ \hline Chip Area (mm\({}^{2}\)) & **0.57** & 1.14 & 0.72 & 2.97 & 1.4 & 0.5 \\ \hline Technology & **55 nm** & 40 nm & 40 nm & 65 nm & 0.35 \(\upmu\)m & 0.18 \(\upmu\)m \\ \hline \hline \end{tabular}  
* Graphically estimated; ** measurement results; *** post-layout simulation results.  
\end{table}
Table 3: Comparison with other dual-band PAs.  
Figure 22: Simulated IMD3 versus output. At (**a**) 2.4 and (**b**) 5.5 GHz modes.  
require a larger area due to the multi-path linear power combining, which, however, offers a significant gain advantage over other power amplifiers. The remaining amplifiers utilize a single-stage amplification structure, resulting in a smaller occupied area but consequently lower gain. In summary, the proposed dual-band power amplifier has a compact footprint and demonstrates a distinct advantage in output power. Additionally, it achieves a favorable trade-off between gain and efficiency, making it well-suited for dual-band IEEE 802.11 ax applications.  
To continuously boost data throughput, WLAN standards are progressively increasing bandwidth, optimizing spectral efficiency, and adopting more complicated modulation schemes, which pose more stringent linearity and efficiency requirements on power amplifiers. The future research focus for power amplifiers in WLAN applications may aim at improving linearity and efficiency at power back-off levels while meeting high linearity requirements in broadband or multi-band switching conditions