# Experimental Test of Continuous Wave Frequency Diverse Array Doppler Radar +
## 6 Concluding Remarks  
In this work, we present the data collected from four different experimental test setups of a linear CW FDA radar, with an emphasis on the signal-model-level agreement between theoretical analysis and experimental results. These collections also showcase the potential utility of the FDA as a low-complexity perimeter surveillance system with an auto-scanning mainbeam feature.  
We experimentally demonstrated the following:  
* Two key attributes of far-field pattern: temporal periodicity and angular scanning behavior of the mainbeam.
* Basic radar capabilities through binary target detection tests in a controlled anechoic environment.
* Doppler shift from two moving targets: a car and a drone.
* Extraction of micro-Doppler features from rotating blades using the STFT as a tool for time-frequency analysis.  
In conjunction with our work in [31], where we capture the fast-time response of a linear FDA using fast-time binary phase-shift keying (BPSK) modulations at each element, this collective body of work provides a solid experimental exploration of the linear FDA at the signal model level.  
Future work in this area would see an expansion of the current system into larger linear arrays, as well as planar array architectures, to experimentally capture fast-time behaviors from advanced FDA frequency offset schemes and array architectures (see Section 1) often seen in the academic literature.  
In this work, differences can be seen in the experimental and theoretically expected values. Sources of experimental error include SDR phase noise, hardware timing mismatch, and non-ideal antenna locations. Thus, sensitivity studies are also pertinent next steps in the evolution of this research thrust. Existing motivation for such work can be found in [10, 11, 58, 59], where FDA manifold sensitivity, beampattern sensitivity due to frequency offset error, and phase noise sensitivity are studied. The theoretical analysis can be extended with data collections and subsequent analysis and study using different FDA transmit/receive architectures.  
Conceptualization, B.C.J. and R.M.N.; methodology, B.C.J.; software, N.R.M.; validation, N.R.M.; formal analysis, B.C.J. and R.M.N.; investigation, B.C.J. and N.R.M.; resources, R.M.N.; data curation, N.R.M.; writing--original draft preparation, N.R.M. and B.C.J.; writing--review and editing, N.R.M., B.C.J., R.M.N. and T.D.B.; visualization, N.R.M.; supervision, B.C.J., R.M.N. and T.D.B.; project administration, B.C.J. and R.M.N.; funding acquisition, R.M.N. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the US Office of Naval Research grant number N00014-20-1-2160.  
**Data Availability Statement:** The datasets presented in this article are not readily available because of sponsor restrictions.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline \(\mathbf{K^{sys}}\) (\# of Blades) & \(\mathbf{\Lambda_{0}^{sys}}\) (m) & \(\mathbf{\Omega^{sys}}\) (rad/s) & \(\mathbf{L_{KD}^{sys}}\) (m) & \(f_{mD}^{calc}\) (Hz) & \(f_{mD}^{meas}\) (Hz) & \(\mathbf{L_{KD}^{est}}\) (m) \\ \hline
1 & 0.0508 & 5.24 & 0.165 & 34 & 36 & 0.175 \\
2 & 0.0508 & 5.24 & 0.145 & 29.8 & 32 & 0.155 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Estimated (est) and calculated (calc) propeller blade length comparison. Note (meas) and (sys) represent experimentally measured and implemented system parameters, respectively.  
**Conflicts of Interest:** Author [PERSON] was employed by the company ARKA Group, L.P. RST. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.