# A Miniaturized Design for a Terahertz Tri-Mirror CATR with High QZ Characteristics
## 3 Simulation and Measurement Results
After the fabrication and assembly of the designed tri-mirror CATR, the QZ generated by the prototype was scanned and performance-tested using the NSI planar near-field  
Figure 8: Manufactured physical prototype of corrugated horn feeds for the tri-mirror CATR: (**a**) with center operating frequency of 183 GHz; (**b**) with center operating frequency of 275 GHz. Figure 7: The physical prototype of the fabricated miniaturized tri-mirror CATR system. scanning system. Figure 9 shows the schematic diagram of the planar near-field test for the QZ of the designed tri-mirror CATR prototype. The entire testing procedure begins with the control computer issuing test commands. Subsequently, the built-in fundamental signal source of the Vector Network Analyzer N5242A (VNA) transmits signals, which are processed by a transmitting module incorporating a power amplifier and a frequency extender to generate terahertz signals across different frequency bands. These signals are then radiated as quasi-planar waves from the feed source toward the main reflector of the CATR under test via the transmitting module. Next, a signal-receiving scanning probe connected to the signal reception module on the NSI High-Precision Planar Near-Field Scanner scans and captures the field distribution within the QZ plane at a specified distance perpendicular to the quasi-planar waves. The received signals are modulated by a receiving module with a low-noise amplifier (LNA) and fed back into the VNA. Finally, through data processing and analysis, various QZ performance parameters are obtained. The entire testing process is controlled by the NSI-300V-12x12 software. Figure 10 depicts the planar near-field testing environment for the designed tri-mirror CATR. The NSI planar near-field scanner features a scanning range of 2.4 m \(\times\) 2.4 m, a flatness better than 5 \(\upmu\)m, and a testing frequency up to 500 GHz. A vertical plane located 75 cm from the center of the primary mirror was selected as the QZ scanning plane, with a scanning area of 20 cm \(\times\) 20 cm and a sampling grid of 101 \(\times\) 101 points. Figure 10: NSI planar near-field test scanner used for the designed tri-mirror CATR testing. Figure 9: Schematic diagram of the planar near-field test for the QZ of the tri-mirror CATR. For the developed tri-mirror CATR, its operating frequency covers multiple frequency bands, while the bandwidth of a single horn feed is relatively limited. Thus, measurements across the full frequency range of the system can be achieved by replacing the horn feeds and corresponding frequency extension modules for different bands. Constrained by the frequency extension modules available on the near-field testing platform, two corrugated horns with central operating frequencies of 183 GHz and 275 GHz, as shown in Figure 8, are used to feed the miniaturized tri-mirror CATR system. Figures 11 and 12 present the measured QZ field distribution curves of the co-polarization amplitude/phase and cross-polarization amplitude of the major cuts of the horizontal and vertical planes at 183 GHz and 275 GHz, respectively. As shown in Figures 11 and 12, the measured QZ results at 183 GHz and 275 GHz indicate that the co-polarization amplitude ripples within the QZ of the CATR system are all within 1.8 dB. The co-polarization phase ripples are all within 11\({}^{\circ}\), except for significant fluctuations in the horizontal direction at 183 GHz, and the QZ usage ratio reaches 70%. Additionally, the co-polarization amplitude and phase of the QZ field in the central region exhibit overall flat distributions, while rapid attenuation occurs on both edges, which is consistent with the previous simulation results of the system. The pronounced phase  
Figure 11: The measured QZ field distribution curves for the designed miniaturized tri-mirror CATR at 183 GHz: (**a**) the measured co-polarization amplitude distribution; (**b**) the measured cross-polarization amplitude distribution; (**c**) the measured co-polarization phase distribution.