300-GHz Versatile Transceiver Front-End for Both Communication and Imaging A. Kanno * , N. Sekine * , Y. Uzawa * , I. Hosako * , and T. Kawanishi *† * National Institute of Information and Communications Technology 4-2-1 Nukui-kitamachi, Koganei, Tokyo 184–8795, Japan Email: kanno@nict.go.jp † Waseda University, 3-4-1 Ohkubo, Shinjuku, Tokyo 169–8555, Japan. Abstract—Envelope-detector-based transceiver configurations are useful for both digital signal transmission and radar systems in the terahertz band. A dual-purpose transceiver is demon- strated using a 1-Gb/s on-off keying signal and 12.5-GHz- bandwidth frequency-modulated continuous-wave radar. I. I NTRODUCTION T ERAHERTZ waves are promising for both high-speed wireless communication and precision imaging because of their short wavelengths. In practice, terahertz-band trans- mission with a capacity greater than 20 Gb/s has already been reported with an on-off keying (OOK) scheme [1]. Additionally, concealed material detection by the terahertz waves is useful for enhancing civil security. Short wavelengths allow small object detection at sizes comparable to the wave- length (less than several centimeters for terahertz waves). Specifically, in a frequency-modulated continuous-wave (FM- CW) radar system, the range resolution is inversely propor- tional to the bandwidth of the radar signal, and therefore, a broad bandwidth in the terahertz band would provide high resolution radar, unlike microwave and millimeter-wave radar. For communications, especially in OOK and radar systems, many devices in a transceiver can be shared, such as amplifiers, detectors, and transmitter/receiver separators in the antenna. However, evaluation and demonstration for communication and radar systems are independently performed because of complicated transceiver configurations. In the paper, we configure a versatile transceiver front-end in the terahertz band connected to photonics-based transmitters for communication and radar signal generation. An envelop detector is utilized to convert from a 300-GHz OOK signal to the baseband for communication; this detector is also used as a simple radar mixer to regenerate a beat note between the original signal of the transmitter and the incoming signal from an antenna. II. EXPERIMENTAL SETUP Figure 1 shows the setup of the 300-GHz transceiver. Photonics-based transmitters generate a 300-GHz-band optical signal for the baseband signal transmission with a 1-Gb/s OOK and for the FM-CW radar system with a signal bandwidth of 12.5 GHz [2]. In the front-end, a high-speed photomixer (PM) based on a uni-traveling-carrier photodiode converts the PM SBD Photonic FM-CW gen. Photonic OOK gen. ADC (Scope) BERT LNA Y-coupl. Feeder horn Offset parabora Fig. 1. Configuration of versatile transceiver frontend. optical signal into a 300-GHz terahertz-wave signal. A low- noise amplifier (LNA) amplifies the signal sent to the 3-dB Y-coupler. The amplified signal is radiated by a feeder horn antenna connected to an offset parabolic antenna with a total gain of 46 dBi. Incoming 300-GHz signals are collected by these antennas. Then, the received signal is boosted by the LNA, which is located after the Y-coupler. A Schottky barrier diode (SBD) performs envelope detection to convert the signal into a baseband signal. An analog-to-digital converter (ADC) and bit-error-rate test set (BERT) are used to evaluate the signal quality for the radar signal and communication signal, respectively. It should be noted that the Y-coupler has 20- dB isolation between the input (for the transmitter signal) and the output port (to the receiver). This isolation helps achieve a small signal leakage from the input signal to the receiver. It is important for FM-CW radar that ranging in the FM-CW scheme is performed by obtaining the beat note between the original signal and the incoming (delayed) signal. Generally, the leakeage degrades the received signal quality for the communication. The 20-dB isolation did not affect the communication receiver. III. DEMONSTRATION For the proof-of-concept demonstration, communication signal transmission and radar demonstration are performed. For the signal transmission, a 1-Gb/s OOK signal is used as the signal under test; its pattern is a pseudo random bit stream with a length of 2 31 -1. The transmitted signal from the antenna was reflected from a metal plate located in front of the antenna. Then, the reflected signal is input to the receiver. Figure 2(a) shows the observed OOK eye pattern; a clear eye opening is shown with a pulse duration of 1 ns. On the other hand, for the radar demonstration, beat note spectra mixed by the SBD with various distances of the target (a metal plate) are shown in Fig. 2(b). The FM-CW signal has a bandwidth