Foundations For Microwave Engineering

Ferromagnetic microwires enabled multifunctional composite materials

Synthesis and electromagnetic characterization of frequency selective radar absorbing materials using carbon nanopowders

In this letter, a novel low-profile microstrip-fed compact triple band-notched ultrawideband (UWB) antenna is proposed. Notch bands around the 3.3-3.8-GHz WiMAX and 5.15-5.85-GHz WLAN frequencies are obtained by etching out two elliptic single complementary split-ring resonators (ESCSRRs) of different dimensions from the radiating patch of the antenna. Furthermore, by placing two rectangular split-ring resonators near the feedline-patch junction of the antenna, rejection for the 7.9-8.4-GHz X-band frequencies is achieved. Design guidelines for implementing the notch-bands at the desired frequency regions are provided. The match between the simulated and experimental results suggests that the proposed antenna can be a good candidate for application in UWB communication systems.

A Compact Microstrip-Fed Triple Band-Notched UWB Monopole Antenna

In this paper, we present the design of nanostructured multilayer absorbers, carried out with the aid of a genetic algorithm (GA). Waveguide measurements are performed to recover the dielectric properties of micrographite single-walled carbon nanotube, micrographite walled carbon nanotube, carbon nanofiber, and fullerene-based composite materials. Conductive fillers are uniformly dispersed in an epoxy resin at different weight percentages (1, 3, 5 wt.%). The electromagnetic (EM) analysis is performed embedding the forward/backward propagation matrix formalism in an in-house GA, thus able to carry out optimization upon oblique incidence over a finite angular range. Developed code minimizes both the reflection and the transmission coefficients under the thickness minimization constraint. Comparison between micrographite and nanopowders absorbers is presented and discussed, when a broadband quasi-perfect absorber is achieved among the X-band combining the two filler families, i.e., exhibiting a loss factor greater than 90% in most of the band, for a thickness of about 1 cm. It is demonstrated that the nanofillers with higher aspect ratio mainly contribute to the EM absorption. Findings are of interest in both radar-absorbing material and shielding structures.

Broadband Electromagnetic Absorbers Using Carbon Nanostructure-Based Composites

In this paper, a symmetric four-port microwave varactor based 90 ° directional coupler with tunable coupling ratios and reconfigurable responses is presented. The proposed coupler is designed based on the modified structure of a crossover, where varactors are loaded. By applying suitable biasing voltages to the varactors, the power-dividing ratios between the two output ports (i.e., port 2 and port 3) of the coupler can be easily controlled. Moreover, it is found that the realizable power ratio using the proposed structure is very flexible (it could be extremely large or small). Therefore, under the special case when the coupling ratio is tuned to be 1, the proposed coupler is reconfigured to be a crossover. Good isolation and return-loss performance have been maintained for different power-dividing ratios. To theoretically analyze the proposed device, closed-form design equations are derived using the even-odd mode method. Based on these analytical equations, an experimental prototype working at 1 GHz is designed, fabricated, and characterized. The measurement results match well with the simulation and theoretical results, validating the proposed design theory.

A Varactor Based 90 $^{\circ}$ Directional Coupler With Tunable Coupling Ratios and Reconfigurable Responses

Multiwalled carbon nanotubes (MWNTs) are characterized at X-, Ku-, Ka-, and Q-bands by rectangular waveguide measurements. The scattering parameters (S-parameters) of thin MWNT papers containing a large ensemble of randomly oriented nanotubes are measured by a vector network analyzer from 8 to 50 GHz. A rigorous extraction algorithm has been developed to compute the effective complex permittivity ( epsiv = epsiv'- jepsiv") and permeability ( mu = mu' - jmu") of the nanotube papers from the measured -parameters. The extracted effective medium parameters are verified by finite-element simulations using Ansoft's High Frequency Structure Simulator (HFSS). The uncertainties for this characterization method are analyzed. The systematic uncertainties are found larger at lower frequencies than at higher frequencies. The extracted conductivity of the nanotube papers is in the range of 810-1500 S/m and the dielectric constant is from 250 to 700. The extracted complex permittivity can be fitted with the Drude-Lorentz model for the 8-50-GHz frequency range. The effective medium theory is then applied to remove the impact of air in the nanotube paper.

Microwave (8–50 GHz) Characterization of Multiwalled Carbon Nanotube Papers Using Rectangular Waveguides

Two-dimensional (2-D) metallic wire arrays are studied as effective media with an index of refraction less than unity (n eff < 1) The effective medium parameters (permittivity ?eff, permeability ?eff and neff) of a wire array are extracted from the finite-element simulated scattering parameters and verified through a 2-D electromagnetic band gap (EBG) structure case study A simple design methodology for directive monopole antennas is introduced by embedding a monopole within a metallic wire array with (n eff < 1) at the antenna operating frequencies The narrow beam effect of the monopole antenna is demonstrated in both simulation and experiment at X-band (8-12 GHz) Measured antenna properties including reflection coefficient and radiation patterns are in good agreement with simulation results Parametric studies of the antenna system are performed The physical principles and interpretations of the directive monopole antenna embedded in the wire array medium are also discussed

Metallic Wire Array as Low-Effective Index of Refraction Medium for Directive Antenna Application

In this study, a water-based rectangular dielectric resonator antenna is designed and analysed. The compactness of the antenna because of the high relative permittivity of water is demonstrated in both simulation and experiment. In addition, a dielectric resonator antenna-based technique is proposed for measuring liquid permittivities. The resonance frequencies of the antennas with fixed configurations are obtained from finite-element electromagnetic (EM) simulation for liquids with different permittivity values. An analytical model of liquid permittivity as a function of the antenna resonance frequency is then developed. Based on this predictive model, the measurement of the liquid real relative permittivity can be easily achieved by measuring the antenna resonance frequency. The measured permittivity values of distilled water and 10% glucose solution are in agreement with previous data in the literature, demonstrating the effectiveness of the proposed liquid permittivity measurement technique.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-map.2013.0447

Liquid-based dielectric resonator antenna and its application for measuring liquid real permittivities

Printed elliptical monopole antennas are discussed for ultra wideband (UWB) applications. To enhance the design flexibility of the UWB antennas, two slots are incorporated along the edges of the elliptically shaped monopole. By adjusting the size of the slots, the overall performance of the proposed antenna can be improved. Full wave electromagnetic simulations have been used to investigate the effects of different parameters (feed-line length, monopole shape, etc.) on the antenna performance. To verify the design concept, a prototype antenna was designed on the Rogers' RT/Duroid 5880 substrate, fabricated and characterized experimentally. The measured properties of the antenna, including return loss, radiation pattern, and gain, show good agreement with the predicted UWB behavior. Moreover, as a result of the flexibility provided by the proposed designs, an antenna that incorporates a notch frequency within the UWB band is easily achieved. This notch-filter antenna design is also presented along with its simulated performance. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 466–471, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24943

Rongguo Zhou

Papers

A Varactor Based 90 $^{\circ}$ Directional Coupler With Tunable Coupling Ratios and Reconfigurable Responses

Microwave (8–50 GHz) Characterization of Multiwalled Carbon Nanotube Papers Using Rectangular Waveguides

Metallic Wire Array as Low-Effective Index of Refraction Medium for Directive Antenna Application

Liquid-based dielectric resonator antenna and its application for measuring liquid real permittivities

Designs of ultra wideband (UWB) printed elliptical monopole antennas with slots