**2. System Architecture**

Figure 1 shows the system block diagram of the channel emulator and its connection to an RF system. The whole N-channel system includes three parts: baseband, LO signal source, IF chain, and RF front-end. Among them, the research on baseband (BB), Lo signal source, and IF TX/RX is relatively mature. However, there are few research reports on RF channel emulators. An E-band specific RF front-end chip for channel emulator applications is currently scarce in the market. Therefore, in this paper we develop a channel simulator for evaluating E-band channel characteristics for future E-band communication application scenarios.

The red dotted box in Figure 1 shows the system block diagram of the 66–67 GHz channel emulator module designed in this paper. The transceiver chip is realized by cascading a frequency tripler, the first LO band-pass filter (BPF), a LO driver amplifier, the LO high-pass filter (HPF), a mixer, and the second RF BPF [4]. The LO chain integrates a tripler instead of a doubler or higher order frequency multiplier in order to make a compromise between test convenience, conversion gain, and power consumption. Additionally, the tripler was chosen to have a trade-off between the cost of the LO signal source and power consumption. The IF frequency is selected around 27 GHz in the 5G mm-wave hotspot frequency band to facilitate the measurement of the channel emulator. In order to facilitate the connection with the instrument and the TX module, the IF and LO are coaxial interfaces, and the LO and IF ports of the transceiver are connected to the module via microstrip gold wire bonding. The RF output port of the module is a WR12 waveguide interface, as shown in Figure 1.

The mixer in the system architecture is a passive star mixer, so the channel emulator can be used for TX testing or RX testing. When applied to TX test scenarios, the RF signal output power budget is between −50 dBm and 0 dBm over 66-to-76 GHz. When an RX is tested, the input power range of the RF signal is −45~0 dBm. In addition, for the channel emulator, the transmit output power and receive noise figure are not key indicators, so the RF power amplifier and low noise amplifier are not integrated in the system [7,8]. To the best of our knowledge, extensive research has been carried out on

mm-wave transceivers [9–12], while studies have rarely been published concerning E-band radio channel emulator application.

**Figure 1.** System block diagram of the channel emulator system.

#### **3. Circuit Design Methodology**

In this section, we will present the circuit design methodology of the 66–67 GHz channel emulator, including the consideration of each block, and then present the simulated and measured results of key building blocks.
