# A Wideband Dielectric Waveguide-Based 160-GHz Radar Target Generator
## 5 Measurements  
The functionality of the RTG was verified in measurements with a single-channel 160-GHz radar and compared to radar measurements with free-space propagation. The ramp duration of the FMCW radar was set to 1 ms with a bandwidth of 19.2 GHz at the center frequency of 153.6 GHz. The range spectrum was calculated by averaging over 500 ramps. In Figure 10(b), the measured mean value and standard deviation of the range spectrum with the RTG is shown. The metal cuboid target was positioned at a distance of \(L_{\text{mech}}=2\) m resulting in a measured length of 2.53 m. Compared to Figure 4 \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Unit** & **Description** \\ \hline \(\lambda_{0}\) & 1.875 & mm & free-space wavelength \\ \(G\) & 27 & dBi & antenna gain \\ \(|\Gamma_{1}|\) & \(-7.73\) & dB & water reflection coefficient \\ \(|\Gamma_{2}|\) & \(-16.72\) & dB & palm oil reflection coefficient \\ \(a_{\text{davg}}\) & 3 & dB/m & attenuation dielectric waveguide \\ \(a_{\text{wg}}\) & 0.7 & dB & attenuation waveguide and mode transformer \\ \(a_{t}\) & 3 & dB & attenuation MMIC transition \\ \(l_{s}\) & 1.27 & & extension factor \\ \(r_{1}\) & \(-6\) & dB & cuboid reflection coefficient \\ \(r_{2}\) & \(-16\) & dB & cylinder reflection coefficient \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Link-budget parameter for free-space propagation and the radar target generator (RTG). Figure 10: Power ratio \(P_{r}/P_{t}\) for a radar with free-space propagation and the RTG. The ratio is simulated for water (**a**) and palm oil (**b**). with a simulated extension factor \(l_{s}=1.57\), the extension factor was reduced to \(l_{s}=1.27\) due to the smaller waveguide dimensions. The normalized power level for the cuboid target (water) was 10.9 dB above the power level of the cylinder target (palm oil, Figure 11c). The measured level difference agreed very well with the expected theoretical value of 10.2 dB. The additional target at 2.21 m was a ghost target and resulted from a generated subharmonic at 11/12 of the transmit frequency \(f_{t}\) within the prototype radar sensor. The power level of the subharmonic was 15 dB below the target power level. The holder at 1 m caused a reflection at 1.26 m with a normalized power level of \(-42\) dB. Due to the reflection of the transition from the monolithic microwave integrated circuit (MMIC) to the dielectric waveguide, a target at 7 cm is measured. The increased noise power behind the target results from target holder reflections. In comparison to the RTG measurements, a radar measurement with an extended metal plate at a distance of 2.53 m with \(|\Gamma|=1\) is shown in Figure 11a. The target power level of \(-8.1\) dB was equal to the power level of the metal cuboid. According to the link budget in Figure 10 the level difference at 2.53 m was 18 dB. Due to the different reflection factors in the measurement, the power difference is reduced by 12 dB. The remaining difference of 6 dB resulted from the spread target peak by dispersion (cf. Figure 4), which was neglected in the link budget. The ghost target resulting from the first subharmonic was shifted to a distance of 2.32 m due to the different group velocity and the different extension factor at lower frequencies. The second ghost target at 2.10 m resulted from a second subharmonic (5/6 \(f_{t}\)) and its power level was 36 dB below the target power level. This subharmonic was not visible in the RTG spectrum, since the frequencies were not propagable on the dielectric waveguide and were radiated instead. The range spectrum of the free-space radiating radar had a noise level of around \(-83\) dB and was 20 dB below the noise level of the RTG. The increased noise floor of the RTG is caused by inhomogeneities in the dielectric waveguide. This resulted in reflections, which were not averaged but are still below the noise floor of one measurement.