## 4 Experimental Results
### Comparison  
A comparison of the conversion ability of several microwave photonic converters was completed and the results are presented in Table 2. In [28; 29; 30], the research was carried out based only on the downconversion, and practical application as a transceiver is limited. Apart from this, the bandwidth limiting factors, including optical and electrical devices, are more than the proposed microwave photonic converter for the entire system. Considering the purity of the electrical spectrum, we find that [28; 30] just show spurious suppression within a fraction of the bandwidth, but our converter has a suppression ratio of the mixing spurs >40 dBc in the whole in-band of 0.8-18 GHz.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Schemes** & **Conversion Type** & **Conversion Efficiency** & **Purity of Electrical Spectrum** & **Modulation Mode** & **Limitation of Bandwidth** & **Demonstrated Bandwidth** \\ \hline
[28] & Downconversion & 8.8 dB & \
\begin{tabular}{c} Good (spurious \\ suppression \(>\) 40 dBc \\ in 90–110 MHz) \\ \end{tabular} & CS-SSB &
\begin{tabular}{c} Edge roll-off of \\ optical filter and \\ DPMZM \\ Edge roll-off of \\ optical filter and \\ MZM and \\ DPM-MZM in \\ series \\ \end{tabular} & 6–40 GHz \\
[29] & Downconversion & \(-\)3.5 dB & Not measured & CS-DSB &
\begin{tabular}{c} Edge roll-off of \\ DPMZM \\ Edge roll-off of \\ optical filter and \\ MZM and \\ DPM-MZM and \\ series \\ \end{tabular} & Not measured \\
[30] & Downconversion & \begin{tabular}{c} Around \\ \(-\)27 dB \\ \end{tabular} & \begin{tabular}{c} Good (spurious \\ suppression \(>\) 40 dBc \\ in 400–600 MHz) \\ \end{tabular} & DSB & \begin{tabular}{c} DMZM and \\ PDM-MZM in \\ series \\ \end{tabular} & 2–9 GHz \\ This paper & \begin{tabular}{c} Both upconversion \\ and downconversion \\ \end{tabular} & \
\begin{tabular}{c} Around \\ \(-\)35 dB \\ \end{tabular} &
\begin{tabular}{c} Good (spurious \\ suppression \(>\) 40 dBc \\ in the whole in-band) \\ \end{tabular} & CS-DSB & MZM & 0.8–18 GHz \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of the conversion ability of several microwave photonic converters.  
Figure 8: Input 1 dB power compression point (IP-1), (**a**) for upconversion and (**b**) for downconversion.  
Figure 9: Spurious-free dynamic range (SFDR), (**a**) for upconversion and (**b**) for downconversion.  
On the other hand, we compared the proposed microwave photonic converter to the traditional electrical conversion utilizing an MUC + EF setup. Generally, the traditional electrical converter needs multi-stage conversion when it is used in a transceiver. The one-stage electrical conversion system cannot cover the whole band of 0.8-18 GHz, which means an increase in the system complexity. In order to expand the conversion bandwidth and the number of parallel processing signals, the traditional microwave frequency conversion system needs to continuously increase the number of antennas. Thus, the costs and size will increase. However, the microwave photonics frequency conversion system used in our system does not significantly increase device count as processing demands increase. Therefore, from this perspective, our system is simpler than the MUC + EF setup [31].