Broadband 240-GHz Radar for Non-Destructive Testing of Composite Materials

A broadband frequency-modulated continuous-wave radar that operates at a center frequency of 240 GHz is being presented. The main focus of this paper is on the monolithic integration of the millimeter wave transceiver front end circuit and its validation at the wafer level, module level, and system level. The transceiver front end chip was developed using a 35-nm InAlAs/InGaAs-based metamorphic high electron mobility transistor technology with an advanced back-end-of-line (BEOL) process. The key functional building blocks were developed as part of a broadband integrated circuit library for millimeter wave, and THz phased array applications. The transmit path (TX) of the transceiver has a 3-dB defined bandwidth of 60 GHz, and output power of 8 dBm was measured at the chip level and 6 dBm at the waveguide module level, respectively. The receive path (RX) exhibited a conversion gain of 10 dB and an average noise figure (NF) of 7 dB, which were measured over a 3-dB defined bandwidth of 40 GHz, or a 10-dB defined bandwidth of 60 GHz. The flatness of the TX and RX was 1 dB for the transmit power and NF between 220 and 260 GHz. The radar was evaluated for its application in nondestructive tomographic imaging of multilayer glass fiber-reinforced materials. A focusing scanning system was used to determine the characteristic features of material samples at different bandwidths up to 65 GHz.