# A Miniaturized Design for a Terahertz Tri-Mirror CATR with High QZ Characteristics
## 3 Simulation and Measurement Results  
To validate the QZ characteristics of the designed miniaturized tri-mirror CATR system, numerical simulations and prototype testing of the system are conducted in this section. Figure 3 illustrates the simulation model of the designed system, which is numerically analyzed using the electromagnetic simulation software GRASP-10 based on Physical Optics and Theory of Diffraction algorithms across the 100-500 GHz operating frequency band. During the simulation modeling, all three mirrors are assumed to be made of PEC (Perfect Electric Conductor) material with ideal conductive properties, and the surroundings of the model are set to an ideal environment without reflected waves. In the simulation, the system employs an ideal Gaussian feed with a cross-polarization amplitude under \(-50\) dB, a far-field pattern featuring good symmetry characteristics, and a pattern taper with \(-16\) dB attenuation at \(15^{\circ}\). Figure 2: Configuration structure of the designed miniaturized tri-mirror CATR with low cross-polarization. Figures 4-6, respectively, show the simulated QZ field distribution results for the major cuts of the horizontal and vertical planes for the developed miniaturized tri-mirror CATR system at 100 GHz, 183 GHz, 275 GHz, and 500 GHz. Figure 4: The simulated QZ field cross-polarization amplitude curves of the designed miniaturized tri-mirror CATR system: (**a**) 100 GHz; (**b**) 183 GHz; (**c**) 275 GHz; (**d**) 500 GHz. Figure 3: Simulation model for the developed miniaturized tri-mirror CATR with low cross-polarization. Figure 5: The simulated QZ field co-polarization amplitude curves of the designed miniaturized tri-mirror CATR system: (**a**) 100 GHz; (**b**) 183 GHz; (**c**) 275 GHz; (**d**) 500 GHz. Figure 6: The simulated QZ field co-polarization phase curves of the designed miniaturized tri-mirror CATR system: (**a**) 100 GHz; (**b**) 183 GHz; (**c**) 275 GHz; (**d**) 500 GHz. The simulated outcomes above clearly demonstrate that the tri-mirror CATR achieves co-polar amplitude and phase ripples of 1.6 dB and 10\({}^{\circ}\), respectively, with all cross-polarizations under \(-40\) dB across the major cuts of the QZ in a frequency range of 100-500 GHz. Notwithstanding the presence of undesirable ripples in the central QZ region arising from mirror-edge diffraction effects and the multi-path scattering of stray fields, particularly pronounced at lower frequencies, the co-polarization amplitude and phase profiles of the system's QZ remain sufficiently stable across the operational bandwidth. Analysis of the simulation data further reveals a well-defined QZ diameter of 0.14 m for both co-polar amplitude and phase characteristics in the central region, corresponding to a high QZ utilization ratio of 70%. This outcome validates the superior QZ characteristics of the engineered miniaturized tri-mirror CATR system. The observed disturbances are primarily attributable to edge diffraction phenomena and recirculating wave interactions within the chamber environment, yet the fundamental field uniformity remains preserved across the operational bandwidth. Table 2 summarizes the simulation data of the QZ characteristics of the major cuts of the horizontal and vertical planes within the 0.14 m QZ diameter range for the designed miniaturized tri-mirror CATR. Analysis of the simulation data in Table 2 demonstrates that the engineered tri-mirror CATR achieves broadband operation across 100-500 GHz. At lower frequencies, the co-polarization amplitude and phase ripple values are elevated due to the combined effects of mirror edge diffraction and surface roughness. However, as the operating frequency increases, these perturbations attenuate monotonically, leading to progressive improvement in QZ stability. This frequency-dependent behavior highlights the system's ability to maintain acceptable QZ performance across an extended bandwidth. Although the simulations offer valuable insights into the system's performance, several limitations need to be acknowledged.