# A Miniaturized Design for a Terahertz Tri-Mirror CATR with High QZ Characteristics
## 3 Simulation and Measurement Results
fluctuations in the horizontal direction at 183 GHz can be attributed to misalignment errors in the feed's phase center position and the presence of scattering objects near the system's lateral sides during testing. Although the experimental results at both frequencies are slightly higher than the simulation results, the measured performance remains satisfactory considering fabrication tolerances, calibration uncertainties, and measurement errors, meeting the general requirements for terahertz-band antenna testing. Table 3 lists the measured results of the designed miniaturized tri-mirror CATR at 183 GHz and 275 GHz, respectively. When comparing the measurement results in Table 3 with the simulation results in Table 2, it can be seen that the measured cross-polarization levels of the CATR system at 183 GHz and 275 GHz are \(-25.3\) dB and \(-32.2\) dB, respectively, deviating significantly  
Figure 12: The measured QZ field distribution curves for the designed miniaturized tri-mirror CATR at 275 GHz: (**a**) the measured co-polarization amplitude distribution; (**b**) the measured cross-polarization amplitude distribution; (**c**) the measured co-polarization phase distribution. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Frequency** & **0\({}^{\circ}\)****Co-Pol** & **0\({}^{\circ}\)****Co-Pol** & **90\({}^{\circ}\)****Co-Pol** & **90\({}^{\circ}\)****Co-Polar** & **Cross-Polar** \\
**(GHz)** & **Amp.****(dB)** & **Pa.****(\({}^{\circ}\))** & **Amp.****(dB)** & **Pa.****(\({}^{\circ}\))** & **Amp.****(dB)** \\ \hline
183 & 1.64 & 23.5 & 1.55 & 10.1 & \(-25.3\) \\
275 & 1.03 & 9.7 & 0.98 & 8.6 & \(-32.2\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The measured results of the designed tri-mirror CATR at 183 GHz and 275 GHz. QZ diameter, 0.14 m.  
from the simulated results (\(-44.5\) dB). This discrepancy arises primarily from three interrelated factors: Firstly, the inherent cross-polarization of the corrugated horn (\(-29\) dB, as characterized in Figure 13) directly compromised system performance. Re-simulation using the horn's measured radiation pattern (detailed in Table 4) confirmed this effect, yielding a cross-polarization value of \(-28.1\) dB--closely aligned with the measured \(-25.3\) dB, which highlights the feed's critical role in degrading performance. Secondly, stray-field interactions occurred: Reflections from stainless-steel fixtures--only partially mitigated by absorbers during testing (as shown in Figure 7)--and scattering objects near the test setup contributed to horizontal phase fluctuations (e.g., \(23.5^{\circ}\) at 183 GHz). These non-ideal electromagnetic couplings were not fully captured in the simulation model, contributing to residual discrepancies. Thirdly, fabrication and alignment tolerances also contributed: Surface roughness (\(1\) um RMS), mirror positional errors (\(-20\) um), and feed-phase-center misalignment exacerbated ripples, especially at higher frequencies. These mechanical imperfections, while small in absolute terms, became more pronounced in the narrowband high-frequency regime. Despite these discrepancies, co-polarization amplitude (\(\leq\)1.8 dB ripple) and QZ utilization (70%) aligned well with the simulations, validating the core design methodology. The experimental far-field radiation pattern of the 183 GHz corrugated horn feed shown in Figure 8a is presented in Figure 13.  
As can be seen from Figure 13, the corrugated horn feed exhibits excellent symmetry in co-polarization amplitude and meets the taper requirement of \(-16\) dB attenuation at \(15^{\circ}\), with side-lobe levels below \(-40\) dB. However, its cross-polarization amplitude is only \(-29\) dB. Since this cross-polarization amplitude is significantly higher than that of the ideal Gaussian feed (cross-polarization amplitude \(<-50\) dB) used in previous CATR simulations, feeding the designed CATR system with this corrugated horn feed during testing will inevitably result in higher measured cross-polarization levels in the system's QZ compared to the simulated results.