**5. Measurement Results**

The measurements were performed using two steps. First, the RF transceiver chip was measured with on-chip characterization to obtain accurate conversion gain, dynamic range, and other performances; then, the packaged module was tested. In addition, since the harmonic suppression performance of the LO link is important for the channel emulator, the LO chain was separately processed and the output power of each harmonic was tested; the measured results are illustrated in Figure 12. In the working frequency range of 3×LOIn (39–49 GHz), the output power of the third harmonic of the LO chain exceeds 15 dBm, and the unwanted harmonics suppression of each order exceeds 40 dBc.

**Figure 12.** The measured output power of each harmonic of the LO chain.

The on-chip measurement setup of an up-conversion configuration is shown in Figure 13. In this measurement, the chip is implemented as a transmitter. LO and IF signals are pumped from two signal source Keysight E8257Ds through co-axial cables and probes. The RF signal is measured by a waveguide probe and a spectrum analyzer. As our corresponding band was E-band, the measurements were conducted by two steps and limited by our testing equipment. One is the V-band (50–75 GHz) test and the other is the W-band (75–110 GHz) measurement. For the two setups, different waveguide probes and two kinds of harmonic mixers were applied. To obtain the accurate output power of the chip, power meter was employed. The down-conversion test setup was similar to that in Figure 13, expect that the RF output was changed to input, and the IF input was changed to output.

**Figure 13.** On-chip measurement setup.

Figure 14 shows the measured results of the conversion gain of the RF transceiver chip and the channel emulator module when the LO signal power is 16 dBm and the IF signal frequency is 27 GHz. The measured results show that the conversion gain of the RF chip is between −8 and −12 dB in the 66–67 GHz frequency band. The conversion gain corresponding to the transmit mode and the receive mode are in agreement. The conversion loss measured in the 66–67 GHz band is large, mainly because the output power of the LO chain is low, which is not enough to drive the star mixer. The conversion loss of the channel emulator module integrated with the RF waveguide interface and the LO and IF coaxial interfaces is about 2 dB higher than the on-chip measured results. In addition to the transition between the RF GSG PAD and the WR12 waveguide port, this part of the loss also includes the loss of a section of the IF signal transmission line on the PCB.

**Figure 14.** Measured conversion gain of the RF channel emulator and the module.

Additionally, the in-band harmonic signal has a great influence on the sensitivity of the channel emulator. In this design, the frequency of the IF signal is 27 GHz, the frequency of the LO signal is 13–16.33 GHz, and the frequency of the RF signal is 66–67 GHz. The 5th harmonic of the LO signal falls within the RF band. Therefore, we measured the power of the 5th harmonic of the LO input signal in the RF band, and the results are shown in Figure 14. It can be deduced that within the RF bandwidth, the 5th harmonic leakage amplitude of the LO is less than −63 dBm.

Figure 15 shows the measured results of the RF output power of the channel simulator module varying with the IF input power. The measured input P1 dB of the module is about 10 dBm. In the 66–67 GHz band, the RF output 1 dB compression point is between −2 and −4.5 dBm. For linear channel simulator transceiver application scenarios, considering a certain spurious suppression margin, the dynamic operating power range of the module can reach more than 50 dB. In the down-conversion test, the receiving dynamic range can reach more than 54 dB under the same signal quality.

**Figure 15.** The measured RF output power of the channel emulator varies with the IF input power.

#### **6. Conclusions**

This paper presents a 66–67 GHz channel emulator module in a waveguide package. The module includes a 66–67 GHz transceiver chip processed by a 0.1 μm pHEMT GaAs process, a DC bias network designed on a PCB, and a low-loss ridge microstrip line to a WR12 waveguide transition structure. In each circuit block of the transceiver, the various clutter signals are closely monitored and studied. By integrating multiple frequency-selective filters and a high-isolation mixer in the link, the transceiver achieves good spurious rejection performance. In addition, benefiting from the designed low-loss stepped microstrip-to-waveguide transition structure, the RF output of the module is a WR12 waveguide interface. This makes it easy to interface with commercial E-band instruments to evaluate the performance of the channel emulator module. Measured results show that the channel emulator module can achieve a dynamic operating power range of more than 50 dB in the 66 to 76 GHz frequency band. Due to better dynamic range performance and higher integration, the transceiver chip and module can meet the application requirements of E-band channel simulators.

**Author Contributions:** Conceptualization, P.Z., C.W. and W.H.; methodology, P.Z., C.W., J.S., Z.C. and J.C.; validation, P.Z., C.W. and J.S.; formal analysis, P.Z., C.W. and J.S.; data curation, P.Z., C.W. and J.S.; writing—original draft preparation, P.Z.; writing—review and editing, P.Z.; supervision, J.C. and W.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported in part by the Natural Science Foundation of Jiangsu Province under Grant BK20210206, in part by the National Natural Science Foundation of China under Grant 62101117 and 62188102, and in part by the Project funded by China Postdoctoral Science Foundation under Grant 277393.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
