## 1 Introduction
### Advancements over Prior FMCW Experiments with GDD Technology  
The current work marks a significant departure from previous FMCW experiments utilizing the GDD as it addresses several limitations and introduces key advancements. 1. Enhancements in Beam Splitting for MMW Imaging: From WGP to Waveguide Splitters  
In an earlier experiment [11], a Free-Standing Wire Grid Polarizer (WGP) was employed for beam splitting, dividing the 100 GHz chirped modulated beam into reference and target signals. While effective, this approach suffered from several drawbacks. The WGP required precise alignment and a 360\({}^{\circ}\) rotation to optimize the beam splitting, making it mechanically complex and less stable. The performance of the WGP was highly sensitive to polarization. If the main and reference beams retained the same polarization state after splitting, interference between the two could reduce the signal-to-noise ratio (SNR), thereby degrading the system's overall sensitivity. The use of the WGP increased the complexity of the experimental setup, as proper alignment had to be ensured for effective beam division, adding a layer of effort and potential for error in the quasi-optical configuration. Moreover, due to these limitations, it was not feasible to implement imaging using the WGP, as the mechanical alignment and sensitivity constraints made it unsuitable for more complex configurations like FPAs. In contrast, the current work employs a waveguide splitter module--specifically, the Mi-Wave 635 Series E/H Hybrid Magic Tee--that significantly improves the system's performance. This module offers polarization-independent splitting, thereby minimizing SNR degradation caused by polarization effects. Its compact and robust design allows it to be directly connected to the source, eliminating the need for mechanical alignment and simplifying the overall experimental setup. The reduced complexity of the quasi-optical configuration enhances the ease of implementation and makes the system more reliable and stable for extended use. The waveguide splitter improves the SNR by ensuring that the reference and reflected signals maintain consistent amplitude and phase characteristics, unaffected by polarization changes. Furthermore, the waveguide splitter reduces polarization sensitivity, ensuring consistent performance across a wide range of operating conditions. The waveguide splitter's internal geometry provides effective power-dividing and phase-inverting characteristics, delivering equal-power, in-phase output signals when power is applied to the H-plane arm and equal-power, opposite-phase output signals when power is applied to the E-plane arm. These features are essential for achieving balanced and stable signal splitting. The compact configuration and low insertion loss of the 635 Series Hybrid Tees make them ideal for MMW imaging applications. This configuration is particularly suitable for future implementations of focal plane array (FPA) imaging, where multiple pixelelements are required for capturing spatially resolved images. The waveguide splitter eliminates polarization sensitivity, reduces SNR degradation, and provides the robustness needed for imaging setups, offering a clear advantage over the WGP for modern MMW imaging systems. System Configuration and Quasi-Optical Design  
The quasi-optical design in this study represents a significant improvement over earlier setups. Previous experiments utilized a straightforward configuration with a polyethylene (PE) lens to focus the reference beam onto the GDD in a side configuration. While this approach was sufficient for basic range extraction, it lacked the precision and sophistication necessary for high-quality imaging. The current work introduces an optimized quasi-optical design tailored for imaging applications, significantly enhancing the accuracy and spatial resolution of the system. A key improvement is the integration of a waveguide splitter, which reduces the complexity of the optical setup by directly dividing the FMCW signal into reference and target paths.