Emmanuel Decrossas

Rigorous Characterization of Carbon Nanotube Complex Permittivity Over a Broadband of RF Frequencies

This study presents a comprehensive characterization of the frequency dependence of the effective complex permittivity of bundled carbon nanotubes (CNTs) considering different densities over a broadband of frequencies from 10 MHz to 50 GHz using only one measurement setup. The extraction technique is based on rigorous modeling of coaxial and circular discontinuities using a mode matching technique in conjunction with an inverse optimization method to map the simulated scattering parameters to those measured by a vector network analyzer. The dramatic values of complex permittivity obtained at low frequencies are physically explained by the percolation theory. The effective permittivity of a mixture of nanoparticles of alumina and CNTs versus frequency and packing density is studied to verify the previously obtained phenomenon.

Mode matching technique-based modeling of coaxial and circular waveguide discontinuities for material characterization purposes

In this paper, it is proposed to use a cylindrical cell for the characterization of dielectric material. The extraction of complex permittivity is based on inverse gradient approach where the full-wave simulation results are mapped to experimental data to extract the complex permittivity. As the operational frequency of radio frequency (RF)/microwave devices is increased, it becomes difficult to accurately model waveguide transitions using traditional methods based on meshing such as finite-element method (FEM) where mesh size is determined according to the wavelength. Moreover, these techniques usually require extensive computational resources. Mode matching technique (MMT) is the full-wave tool implemented in this current work. It is used to compute the generalized scattering matrices (GSMs) of the different discontinuities of test setup. These GSMs model precisely discontinuities as they include the effects of all higher-order modes propagating and evanescent. Simulation and experimental results are included to validate the proposed approach for the rigorous modeling of those discontinuities and hence the extraction of complex permittivity.

Engineered Carbon-Nanotubes-Based Composite Material for RF Applications

Electrical properties of nanocomposite materials are extracted to investigate the possibility to engineer novel material for microwave applications. A measurement setup is developed to characterize material in a powder form. The developed measurement technique is applied on nanoparticles of alumina, carbon nanotubes (CNTs), and composite mixture of carbon nanotubes and alumina. The effect of packing density on dielectric constant and loss tangent is thoroughly characterized experimentally. The obtained results show that the real part of effective permittivity may be considerably enhanced by increasing the percentage of conducting nanoparticles. In addition, it is possible to decrease the loss in a material by mixing low-loss dielectric nanoparticles powder in a lossy material.

High-Performance and High-Data-Rate Quasi-Coaxial LTCC Vertical Interconnect Transitions for Multichip Modules and System-on-Package Applications

A new design of stripline transition structures and flip-chip interconnects for high-speed digital communication systems implemented in low-temperature cofired ceramic (LTCC) substrates is presented. Simplified fabrication, suitability for LTCC machining, suitability for integration with other components, and connection to integrated stripline or microstrip interconnects for LTCC multichip modules and system on package make this approach well suited for miniaturized, advanced broadband, and highly integrated multichip ceramic modules. The transition provides excellent signal integrity at high-speed digital data rates up to 28 Gbits/s. Full-wave simulations and experimental results demonstrate a cost-effective solution for a wide frequency range from dc to 30 GHz and beyond. Signal integrity and high-speed digital data rate performances are verified through eye diagram and time-domain reflectometry and time-domain transmissometry measurements over a 10-cm long stripline.

Transceiver array development for submillimeter-wave imaging radars

The Jet Propulsion Laboratory (JPL) is developing compact transceiver arrays housing discrete GaAs Schottky diodes with integrated waveguides in order to increase the frame rate and lower the cost of active submillimeter-wave imaging radar systems. As part of this effort, high performance diode frequency multiplier and mixer devices optimized for a 30 GHz bandwidth centered near 340 GHz have been fabricated using JPL’s MoMeD process. A two-element array unit cell was designed using a layered architecture with three-dimensional waveguide routing for maximum scalability to multiple array elements. Prototype two-element arrays have been built using both conventionally machined metal blocks as well as gold-plated micromachined silicon substrates. Preliminary performance characterization has been accomplished in terms of transmit power, and conversion loss, and promising 3D radar images of concealed weapons have been acquired using the array.

500–750 GHz submillimeter-wave MEMS waveguide switch

This paper presents a 500-750 GHz waveguide based single-pole single-throw (SPST) switch achieving a 40% bandwidth. It is the first ever RF MEMS switch reported to be operating above 220 GHz. The switch is based on a MEMS-reconfigurable surface which can block the wave propagation in the waveguide by short-circuiting the electrical field lines of the TE10 mode. The switch is designed for optimized isolation in the blocking state and for optimized insertion loss in the non-blocking state. The measurement results of the first prototypes show better than 15 dB isolation in the blocking state and better than 3 dB insertion loss in the non-blocking state for 500-750 GHz. The higher insertion loss is mainly attributed to the insufficient metal thickness and surface roughness on the waveguide sidewalls. Two switch designs with different number of blocking elements are fabricated and compared. The overall switch bandwidth is limited by the waveguide only and not by the switch technology itself.

Broadband characterization of carbon nanotube networks

In this paper, the complex permittivity of carbon nanotube networks is extracted over a broadband of frequencies using a non destructive, simple, and low-cost procedure. The structure holding the material under test is a hollow circular waveguide shorted at one end and connected through precision adapter to the 1.85 mm-50-Ω coaxial cable of performance network analyzer. In this testing configuration, discontinuities between different transmission lines are modeled based on the full-wave mode matching technique. In this modeling, all higher-order modes propagating and evanescent are considered in the computation which produces generalized scattering matrices (GSMs). A gradient-optimization method is used to solve the inverse problem and extract the complex permittivity of material under test from the measured magnitude and phase of reflection coefficient. The technique is general and requires only a small fraction of material under test which can be in liquid, pulverized or solid form.

Terahertz antenna arrays with silicon micromachined-based microlens antenna and corrugated horns

We report on two silicon based antennas for future large-format THz focal plane imaging arrays. The silicon-based corrugated horn antenna shows return loss below 15 dB and antenna gain over 20 dB in the 320-360 GHz frequency band. The 1.9 THz silicon microlens antenna has been designed and microfabricated. The simulated 1.9 THz antenna shows good 2-D beam radiation pattern and aperture efficiencies around 85%. It is clear that the silicon-based corrugated horn antenna will work well below 1 THz. However, it would be difficult to fabricate such antennas at frequencies beyond 1 THz due to the requirement of thin silicon wafers which is difficult to handle during the microfabrication. On the other hand, silicon microlens antennas can work in the frequency range of 300 GHz-2 THz or even higher because of the excellent tolerances achievable with microfabrication techniques. One major advantage of these batch processing techniques is that one can get hundreds of antennas on a single microfabrication run, thus reducing fabrication cost and time.

500–600 GHz submillimeter-wave 3.3 bit RF MEMS phase shifter integrated in micromachined waveguide

This paper presents a 500-600 GHz submillimeter-wave MEMS-reconfigurable phase shifter. It is the first ever RF MEMS component reported to be operating above 220 GHz. The phase shifter is based on a micromachined rectangular waveguide which is loaded by 9 E-plane stubs, which can be individually blocked by using MEMS-reconfigurable surfaces. The phase-shifter is composed of three metallized silicon chips which are assembled in H-plane cuts of the waveguide. The measurement results of the first prototypes of the MEMS reconfigurable phase shifter show a linear phase shift of 20° in 10 steps (3.3 bit) and have a return loss better than 15 dB from 500-600 GHz. The insertion loss is better than 3 dB up to 540 GHz, and better than 5 dB up to 600 GHz for all phase states, of which the major part is contributed by the assembly of the microchips between waveguide flanges which has a reproducibility error between 2 and 6 dB measured for reference chips.

CMOS (Sub)-mm-Wave System-on-Chip for exploration of deep space and outer planetary systems

This paper discusses the applicability of CMOS (sub)-mm-Wave System-on-Chips in space explorations of the solar system, especially planetary missions. Specifically assessed are issues related to high levels of radiation encountered in deep space. To exemplify the type of technology infusion that is possible, we specifically feature the incorporation of a previously developed “self-healing” 12/48 GHz CMOS frequency synthesizer into a current planetary sub-mm-wave (or Terahertz) heterodyne receiver instrument (PISSARRO) for the substantial benefit of payload size, area and weight reduction.