D.V. Lioubtchenko

High Permittivity Dielectric Rod Waveguide as an Antenna Array Element for Millimeter Waves

Dielectric rod waveguide antennas of rectangular cross section have a number of advantages over conventional waveguide and horn antennas as an antenna array element. Dielectric rod waveguide antennas have relatively low cost, low losses, a broadband input match and a high packing potential. Additionally the radiation pattern of such antennas is almost frequency independent. In this paper the suitability of Sapphire rod waveguides for an antenna array is studied with simulations and prototype measurements at W band. Strong mutual coupling is observed when the elements are close to each other.

Dielectric Constant Estimation of a Carbon Nanotube Layer on the Dielectric Rod Waveguide at Millimeter Wavelengths

A method has been developed to estimate dielectric properties of a layer containing carbon nanotubes (CNTs) randomly arranged in plane, deposited on a dielectric rod waveguide (DRW). In the framework of this method, a theoretical model of a layered DRW with extended narrow walls and perfect electric conductor walls was used to fit the experimental results. The experimental results were obtained by measuring the wave propagation characteristics ( S11 and S21) of a DRW unloaded and loaded with different CNT layers at 75-110 GHz. The developed model allows derivation of the dispersion equation of the wave excited in the loaded DRW in an analytical form. The propagation constant is then found numerically through the fitting process with measurement results. Additionally, the complex permittivity of the CNT layer can be estimated using the surface conductivity model of the CNT and mixing formulas. Both methods give reasonable and comparable results. The obtained results (ε = 1- j5×103) allow full-wave simulation (e.g., HFSS) of DRW structures loaded with CNT layers with a thickness of 60 nm or more. Simulation and measurement results agree rather well.

Carbon nanotube network varactor

Microelectromechanical system (MEMS) varactors based on a freestanding layer of single-walled carbon nanotube (SWCNT) films were designed, fabricated and tested. The freestanding SWCNT film was employed as a movable upper patch in the parallel plate capacitor of the MEMS. The measurements of the SWCNT varactors show very high tunability, nearly 100%, of the capacitance with a low actuation voltage of 10 V. The functionality of the varactor is improved by implementing a flexible nanocellulose aerogel filling.

Reconfigurable mm-wave phase shifter based on high impedance surface with carbon nanotube membrane MEMS

A novel phase shifter based on high impedance surface (HIS) with carbon nanotube (CNT) membrane MEMS is proposed. The CNT MEMS HIS is integrated into a dielectric rod waveguide (DRW) so that the CNT membrane acts as a movable ground plane. We present a novel fabrication method of the phase shifter being significantly simpler than those previously used. The device performance is verified through numerical simulations that show a theoretical phase shift of 260° with a 7 volt bias applied. So far we have experimentally demonstrated a CNT membrane varactor, where the distance of the CNT membrane and metal patches changed from 2 μm to 0.4 μm with a 10 volt bias.

Dielectric constant measurements of carbon based nanomaterials and silver nanowires at millimeter wave frequencies

The aim of this work is to study dielectric properties of thin carbon nanotube and silver nanowire layers at 75-110 GHz frequency range. The method is based on S-parameter measurements of loaded and unloaded sapphire rod waveguides.

Beam-steering antennas at millimeter wavelengths

In many emerging applications of millimeter waves, electronic focusing and beam steering is needed. We present a survey of mm-wave beam steering antennas, where the necessary phase change for antenna elements is achieved using various electronically tuneable elements, e.g. microelectromechanical systems (MEMS), such as tuneable leaky-wave antennas, shaped lens antennas with integrated switched feed array, active reflectarray, tuneable high-impedance surface, and dielectric rod waveguides with integrated phase shifters. Some early results of our own relevant investigations are also presented.

Optically controlled millimetre wave phase shifter

Phase shifting in a dielectric rod waveguide, loaded with a carbon nanotube layer illuminated with light from a tungsten lamp, was studied experimentally at the frequency range of 75-110 GHz. Close to a linear dependence of phase shift on the optical power intensity with almost independent behavior of the losses is observed The phase shift of 30 degrees with less than 1 dB extra loss for 1.26 mW/mm2 light intensity was achieved.

Antennas for electronic beam steering and focusing at millimeter wavelengths

This paper discusses the prospects of millimeter-wave beam steering antennas, such as tuneable high-impedance surface, dielectric rod waveguide with an integrated phase shifter, tuneable leaky-wave antenna, active reflectarray, and shaped lens antenna with an integrated switched feed array. In these antennas the necessary phase change for antenna elements can be achieved using various electronically tuneable elements, but in our case MEMS are used. Some early results of our investigations are presented.

Millimeter wave conductivity of silver nanowire network

Wave propagation in a dielectric rod waveguide loaded with a layer of silver nanowires was studied experimentally at millimeter wave frequencies. Then based on the measurement results, analytical calculations were used to estimate conductivity of the silver nanowire layer at millimeter wave frequencies. Numerical simulations based on the calculated conductivities were performed and good agreement of simulated and measured results was achieved.

Millimeter wave phase shifters based on dielectric rod waveguide

MEMS varactors and switchers used as a key element for the phase shifters on dielectric rod waveguides are presented. The 32 degree phase shift due to capacity change in MEMS is demonstrated in W band. New approach of the reconfigurable phase shifter with MEMS switchers is discussed in this work.