An Integrated 100-GHz FMCW Imaging Radar for Low-Cost Drywall Inspection
S. M. Hossein Naghavi, Morteza Tavakoli Taba, Mohammed Aseeri, Ehsan Afshari
Abstract
This article presents a 100-GHz system-on-chip frequency-modulated continuous-wave (FMCW) radar for low-cost drywall inspection. The radar operates at the second harmonic and is implemented in 110-nm complementary metal-oxide-semiconductor (CMOS) with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {max}} = 82$ </tex-math></inline-formula> GHz, significantly lowering the fabrication cost. On the transmitter (TX) side, a double negative resistance technique is proposed to support oscillation startup at the fundamental frequency above <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$({f}_{\text {max}}/2)$ </tex-math></inline-formula> . The radar radiates from 95.8 to 100.1 GHz, with a maximum equivalent-isotropically radiated power (EIRP) of 2.6 dBm and 1.3-dB power fluctuation. A modified folded slot as TX antenna provides <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G_{\text {TX}}= 11.4$ </tex-math></inline-formula> dBi and a broadband impedance matching. On the receiver (RX) part, a folded dipole antenna plays the role of a multifunctional electromagnetic structure that, at the second harmonic, it is a receiving antenna with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$G_{\text {RX}}= 8.8$ </tex-math></inline-formula> dBi. At the fundamental frequency, it maximizes the voltage swing across subharmonic mixer transistors using a voltage doubling mechanism, boosting the mixer conversion gain by, ideally, 12 dB. The chip has a die size of 3.3 mm2 and consumes 196 mW of dc power. Also, offset focal-plane imaging is introduced, which reduces the complexity and cost of the imager. Several images from the infrastructures within drywalls have been taken with the best lateral resolution of 8.4 mm and the measured range resolution of 5.1 cm with rectangular windowing. These qualities make this system a low-cost millimeter-wave imager that provides helpful data for plumbers and handypersons before starting a building renovation.