This is the accepted version of a paper published in IEEE Transactions on Terahertz Science and Technology. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.
A very low-profile sub-THz high-gain frequency beam steering antenna, enabled by silicon micromachining, is reported for the first time in this paper. The operation bandwidth of the antenna spans from 220 GHz to 300 GHz providing a simulated field of view of 56 •. The design is based on a dielectric filled parallel-plate waveguide (PPW) leaky-wave antenna fed by a pillbox. The pillbox, a two-level PPW structure, has an integrated parabolic reflector to generate a planar wave front. The device is enabled by two extreme aspect ratio, 16 mm x 16 mm large perforated membranes, which are only 30 µm thick, that provide the coupling between the two PPWs and form the LWA. The micromachined low-loss PPW structure results in a measured average radiation efficiency of −1 dB and a maximum gain of 28.5 dBi with an input reflection coefficient below −10 dB. The overall frequency beam steering frontend is extremely compact (24 mm x 24 mm x 0.9 mm) and can be directly mounted on a standard WM-864 waveguide flange. The design and fabrication challenges of such high performance antenna in the sub-THz frequency range are described and the measurement results of two fabricated prototypes are reported and discussed.
Materials with tunable dielectric properties are valuable for a wide range of electronic devices, but are often lossy at terahertz frequencies. Here we experimentally report the tuning of the dielectric properties of single-walled carbon nanotubes under light illumination. The effect is demonstrated by measurements of impedance variations at low frequency as well as complex dielectric constant variations in the wide frequency range of 0.1-1 THz by time domain spectroscopy. We show that the dielectric constant is significantly modified for varying light intensities. The effect is also practically applied to phase shifters based on dielectric rod waveguides, loaded with carbon nanotube layers. The carbon nanotubes are used as tunable impedance surface controlled by light illumination, in the frequency range of 75-500 GHz. These results suggest that the effect of dielectric constant tuning with light, accompanied by low transmission losses of the carbon nanotube layer in such an ultra-wide band, may open up new directions for the design and fabrication of novel Terahertz and optoelectronic devices.
This is the accepted version of a paper published in IEEE Transactions on Terahertz Science and Technology. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.
This paper reports on a submillimeter-wave 500-750 GHz MEMS waveguide switch based on a MEMSreconfigurable surface to block/unblock the wave propagation through the waveguide. In the non-blocking state the electromagnetic wave can pass freely through the MEMS-reconfigurable surface while in the blocking state the electric field lines of the TE10 mode are short circuited which blocks the wave propagation through a WM-380 (WR-1.5) waveguide. A detailed design parameter study is carried out to determine the best combination of the number of horizontal bars and vertical columns of the MEMS-reconfigurable surface for achieving a low insertion loss in the non-blocking state and a high isolation in the blocking state for the 500-750 GHz band. Two different switch concepts relying on either an ohmic-contact or a capacitive-contact between the contact cantilevers have been implemented. The measurements of the switch prototypes show a superior RF performance of the capacitive-contact switch. The measured isolation of the capacitive-contact switch designed with 8 µm contact overlap is 19 to 24 dB and the measured insertion loss in the non-blocking state is 2.5 to 3 dB from 500-750 GHz including a 400 µm long micromachined waveguide section. By measuring reference chips, it is shown that the MEMS-reconfigurable surface contributes only to 0.5 to 1 dB of the insertion loss while the rest is attributed to the limited sidewall metal thickness and to the surface roughness of the 400 µm long micromachined waveguide section. Finally, reliability measurements in an uncontrolled laboratory environment on a comb-drive actuator with an actuation voltage of 28 V showed no degradation in the functioning of the actuator over one hundred million cycles. The actuator was also kept in the actuated state for 10 days and showed no sign of failure or deterioration.
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