Mahmoud A. El Sabbagh

Miniaturized carbon nanotube-based RF resonator

Carbon nanotubes exhibit high dielectric constants. They have potential for miniaturizing RF and microwave components. In this paper, this property is utilized to realize a miniaturized CNT-based RF resonator. The resonator structure is excited through a 50-Ω copper-based transmission line. The preliminary design is developed using a full-wave High Frequency Structure Simulator (HFSS). Experimentally-extracted frequency-dependent complex permittivities of CNTs are incorporated in HFSS. The measured and simulated results are in close agreement. A comparison with identical graphite-based resonator verifies the unique behavior of CNTs, and confirms their potential for miniaturizing RF components.

Ultra-wideband and compact novel combline filters

This paper presents a novel method of designing ultra-miniaturized cavity based combline filter integrable in PCB technology for EMI filtering. Each combline resonator is designed based on concepts of designing a unit cell of metamaterials. The other design steps follow the conventional design procedure of microwave filters. Choice of metamaterial unit cell leads to extreme size reduction and conventional design method results-in optimum number of resonators. A strong inter-cavity coupling value not realizable with conventional evanescent method is realized by TEM section. Therefore, the final structure is very compact and broadband. The design is realized using multilayer planar technology. A design example is provided where a dramatic reduction of the volume of filter by a factor of 7 is obtained.

Carbon nanotube-based planar transmission lines

In this paper, we explore building planar transmission lines using carbon nanotube (CNT) networks. We are successful in building the transmission lines and verifying the feasibility of potential planar transmission lines where carbon nanotube networks replace the conventional metallic traces. The experimental realization and the two-port microwave measurements of the proposed transmission lines enable accurate extractions of the fundamental parameters showing percolation effects in CNT networks. The frequency-dependent phase velocity characteristics show dramatic reduction compared to the speed of light in vacuum. The large magnitude of extracted complex permittivity for CNT networks also exhibits its percolation performance.

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.

Analysis of tapped-in coupling between combline resonators applicable in wideband filter designs

In this work, the comprehensive analysis of coupling for combline resonators coupled through tapped-in TEM transmission line is presented. The analysis and discussions are based on developed equivalent circuit modeling the physical structure. The effects of lumped elements in this model on coupling value and resonant center frequency are studied. The results confirm the possibility to achieve a wide range of coupling varying from zero to unity. Strong coupling results in the dramatic increase of resonant center frequency. The measurement results for two-coupled planar resonators based on tapped-in coupling method verify the concepts. Therefore, this tapped-in coupling between resonators is an asset in designs of wideband filters. The developed circuit model is useful for early stages of design. The lumped elements are functions of physical design parameters hence the circuit model speeds up the realization process of finding the initial physical dimensions of resonators which satisfy the required coupling matrix and resonant center frequency. Following, full-wave analysis is performed for the final optimization of total filter structure.

CIRCUIT-BASED ANALYSIS OF TAPPED-IN COUPLING BETWEEN COMBLINE RESONATORS APPLICABLE IN WIDEBAND FILTER DESIGNS

We showed that creating coupling between resonators through transverse electromagnetic transmission line directly tapped into both resonators provides a viable solution for the design of wideband microwave components where strong coupling values are required. However, more analysis is needed to explain the coupling mechanism and its limitation. In this work, we present the developed equivalent circuit model which is comprised only of lumped elements for comprehensive analysis of the tapped-in coupling between planar or cavity combline resonators. The efiects of lumped elements which are in correspondence to physical parameters on coupling value and resonant center frequency are derived. The circuit model predicts that this coupling mechanism by adjusting the design parameters of coupling section simply realizes any required strength of coupling between resonators, i.e., from weak values close to zero up to strong values close to unity. Therefore, wideband fllters are easily designed and their bandwidth can be controlled based on inter-resonator tapped- in coupling. This fact is validated through measurements for two- coupled resonators with unloaded resonant frequency of 1.45GHz. The bandwidth is extended to 90% via tapped-in method. The total dimensions of structure are ‚=4 £ ‚=18 £ ‚=72.

Measurement of dielectric properties of carbon nanotube networks used to build planar transmission lines

In this paper, we explore building planar trans-mission line from carbon nanotube (CNT) networks. We are successful in fabricating the transmission line and verifying the feasibility of potential planar transmission lines where carbon nanotube networks replace the metallic lines. The experimental realization and the two-port microwave measurements enabled us to extract accurately the fundamental parameters of the proposed transmission line. The frequency-dependent phase velocity char-acteristics show clearly its dramatic reduction compared to speed of light in vacuum. The complex permittivity of CNT networks is also reported in our work.

Frequency-dependent circuit models of carbon nanotube networks

Frequency-dependent circuit models for carbon nanotube networks are developed. The procedure of extraction include: fabricating planar transmission-line structures for microwave test where CNT networks replace the metallic traces; extracting the transmission-line complex impedance and propagation constant; computing the transmission line parameters per unit length: resistance, inductance, capacitance, and conductance; finally deducing circuit models for CNT networks.

Full-wave modeling of RF front end for successful design of DDR4 interposer for probing purposes

In this work, we present full-wave analysis of the RF front end of DDR4 UDIMM 288 pin used for probing purposes at speeds of 3200 Mbps and beyond. The effect of connector on performance is investigated.

Measurement-based models of carbon nanotube networks

Measurement-based frequency-dependent circuit models for carbon nanotube networks are developed. The procedure of extraction include: fabricating planar transmission-line structures for microwave test where CNT networks replace the metallic traces; extracting the transmission-line complex impedance and propagation constant; computing the transmission line parameters per unit length: resistance, inductance, capacitance, and conductance; finally deducing circuit models for CNT networks.