Terahertz frequencies (about 100 GHz) offer great promise for detecting a wide range of objects, from cancer cells to concealed weapons. To make such high frequencies more practical, researchers at China’s Nanjing University of Science and Technology and the Semiconductor Device Research Laboratory of the China Academy of Engineering Physics developed an on-chip antenna (OCA) capable of high gain and high radiation efficiency at 340 GHz.
The terahertz antenna was designed with a standard 0.13-μm silicon-germanium (SiGe) BiCMOS semiconductor technology without postprocessing. The antenna incorporates a rectangular slop loop etched into the upper wall of a substrate-integrated-waveguide (SIW) circuit to form a magnetic current loop radiator. The SIW structure forms a back cavity to suppress surface waves and separate the radiating aperture from the substrate.
The researchers created both single antenna elements and a 2 × 2 antenna array to demonstrate the concept. The SIW back cavity resonates at the dominant mode, with EM energy accumulating inside the cavity and the cavity preventing energy absorption by the substrate material. The result is an antenna element with high gin and frequency range of 335 to 348 GHz and an antenna array with maximum gain of 7.9 dBi and efficiency of 48% at 340 GHz.
The SiGe BiCMOS process involves seven metal layers fabricated on a 300- μm-thick silicon substrate, with the two top metal layers isolated by a 10-μm-thick silicon-dioxide layer. The silicon substrate has a dielectric constant of 11.9 and resistivity of 10 Ω-cm. The chip size of the standalone antenna is 0.7 × 0.7 mm2 and the antenna array chip measures 1.1 × 1.1 mm2. The OCAs were characterized by means of a commercial vector network analyzer (VNA) and frequency extender for measurements from 220 to 347 GHz. See “340-GHz SIW Cavity-Backed Magnetic Rectangular Slot Loop Antennas and Arrays in Silicon Technology,” IEEE Transactions on Antennas and Propagation, December 2015, p. 5,272.
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