## 4 Conclusions  
In this study, we proposed a micro-nano scale BPF comprising an approximate circular (36-gon) winding inductor and a circinate capacitor using the GaAs-based IPD technology. The equivalent circuit model was established by considering various capacitive and inductive parasitic effects. The three-layer BPF was fabricated in 12 steps using thin-film and photolithography processes. The fabricated BPF had a miniaturized overall size of 1538 \(\upmu\)m \(\times\) 800 \(\upmu\)m (0.029 \(\uplambda_{0}\)\(\times\) 0.015 \(\uplambda_{0}\)). The insertion loss is as low as 0.53 dB, and the 3-dB FBW is as wide as 70.59%, which shows that the measured results share a relatively good consistency with the theoretical prediction and simulation. Furthermore, the proposed BPF can be employed in modern communication systems owing to its high performance and miniaturized size. Additionally, it can also be used as a biosensor due to its quick RF response time and non-contact detection. However, considering that this study did not investigate the lifecycle and compatibility of the device in practical applications, it will be explored and ameliorated in our future research. Furthermore, its selectivity is limited considering it is a low-order device, which will also be improved and studied in our next research to promote the development of the IPD technology in practical applications. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & **Fabrication** & **Circuit** & **Passband** & **3-dB Fractional** & **Insertion** & **Return** \\  & **Process** & **Area \({}^{\ast}\)** & **(GHz)** & **Bandwidth (\%)** & **Loss (dB)** & **Loss (dB)** \\ \hline \multirow{3}{*}{[40]} & \multirow{3}{*}{Glass-IPD} & \(<\)1.00 mm\({}^{2}\) & \multirow{3}{*}{2.6} & \multirow{3}{*}{49.62} & \multirow{3}{*}{0.6} & \multirow{3}{*}{30} \\  & & & 0.018 \(\uplambda_{0}\)\(\times\) & & & \\  & & 0.009 \(\uplambda_{0}\) & & & & \\ \hline \multirow{3}{*}{[41]} & \multirow{3}{*}{Si-IPD} & 0.72 mm\({}^{2}\) & \multirow{3}{*}{2.4} & \multirow{3}{*}{33.33} & \multirow{3}{*}{2.3} & \multirow{3}{*}{10} \\  & & 0.024 \(\uplambda_{0}\) & & & & \\ \hline \multirow{3}{*}{[42]} & \multirow{3}{*}{Si-IPD} & 3.9 mm\({}^{2}\) & \multirow{3}{*}{1.7} & \multirow{3}{*}{\(\approx\)17.72} & \multirow{3}{*}{2.54} & \multirow{3}{*}{12} \\  & & 0.037 \(\uplambda_{0}\) & & & & \\ \hline \multirow{3}{*}{[43]} & \multirow{3}{*}{Glass-IPD} & 1.69 mm\({}^{2}\) & \multirow{3}{*}{2.1} & \multirow{3}{*}{\(\approx\)8.6} & \multirow{3}{*}{3.2} & \multirow{3}{*}{22} \\  & & 0.019 \(\uplambda_{0}\) & & & & \\ \hline \multirow{3}{*}{This work} & \multirow{3}{*}{GaAs-IPD} & 1.23 mm\({}^{2}\) & \multirow{3}{*}{1.53} & \multirow{3}{*}{70.59} & \multirow{3}{*}{0.53} & \multirow{3}{*}{26.49} \\  & & 0.029 \(\uplambda_{0}\) & & & & \\ \cline{1-1}  & & 0.015 \(\uplambda_{0}\) & & & & \\ \hline \hline \end{tabular} \({}^{\ast}\uplambda_{0}\) is the guided wavelength of the operation frequency.  
\end{table} 
Table 4: Performance comparison of the proposed BPF and published BPFs. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & **Manufacturing** & **Fractional** & **Insertion** & **Return** & **Passband** & **Circuit Area** \\  & **Technology** & **Bandwidth (\%)** & **Loss (dB)** & **Loss (dB)** & **(GHz)** & **Circuit Area** \\ \hline \multirow{2}{*}{[44]} & Microstrip & 13.3 & 1.1 & \(>\)20 & 0.975 & 0.094 \(\uplambda_{0}\)\(\times\) 0.08 \(\uplambda_{0}\) \\ \hline \multirow{2}{*}{[8]} & HTS & 66.7 & 0.2 & 19 & 1.5 & 20.8 \(\times\) 16.15 mm\({}^{2}\) \\  & HTCC & 5.5 & 1.8 & \(>\)15 & 2.25 & 0.182 \(\uplambda_{0}\)\(\times\) 0.156 \(\uplambda_{0}\) \\ \hline \multirow{2}{*}{[5]} & LTCC & 12.5 & 2.4 & 15 & 2.4 & 6.9 \(\times\) 39.9 mm\({}^{2}\) \\ \hline \multirow{2}{*}{This work} & GaAs IPD & 70.59 & 0.53 & 26.49 & 1.53 & 1.538 \(\times\) 0.8 mm\({}^{2}\) \\  & & & & & (0.029 \(\uplambda_{0}\)\(\times\) 0.015 \(\uplambda_{0}\)) \\ \hline \hline \end{tabular}
\end{table}