Submillimeter-wave active radar imager

The authors have developed and demonstrated 3D imaging using a submillimeter-wave FMCW radar with a fast microwave chirp and phase coherent detection. The technique provides an important advantage over more traditional CW RF imaging in that time gating of the return signals allows optimization of the received scene illumination or specific depth reconstruction. This can be used to enhance (or hide) specific objects or greatly reduce background clutter. The system was initially prototyped with available RF components near 600 GHz and a 12.6 GHz chirp producing a 250 MHz/msec sweep yielding a range resolution of 1.2 cm. Lateral resolution on the scene is set by a 20 cm diameter Teflon lens antenna producing approximately 2 cm at 4 m distance. The RF transmit power (generated by a W-band power amplifier and an in-house frequency multiplier chain) is less than 0.5 mW but when coupled with a heterodyne downconverter (in-house developed fundamental balanced Schottky diode mixer, 4000 K DSB noise temperature) yields a measured dynamic range of more than 70 dB. A more compact and higher resolution system is currently under construction and will employ an 18 GHz msec sweep rate microwave chirp for sub-cm range resolution, a 40 cm reflector and a higher power transmitter, dramatically increasing resolution and dynamic range. The talk will cover the system design and some early results we have obtained on test targets at 4 m.