Junyan Tang

An origami tunable metamaterial

The transmission characteristics of a folded surface decorated with a periodic arrangement of split-ring resonators is investigated. The folding pattern has one displacement degree of freedom, allowing motion that can be used to adjust the separation between the rings. When the geometry of the folded surface is varied by mechanical means, the change in spacing between the rings causes a shift in resonance frequency, making the surface mechanically tunable.

Origami Tunable Frequency Selective Surfaces

A foldable frequency selective surface (FSS) is introduced that may be tuned by changing the folding state. The FSS comprises periodic elements arranged in an origami-like fashion on a dielectric sheet. By folding and unfolding the FSS, the interaction with the incident field and the mutual interactions between the elements may be altered, resulting in a shift in resonance frequency. A sample design of a tunable FSS folded into a chevron pattern and decorated with cross-shaped copper prints allows a 19% shift of resonant frequency with a change in folding angle of 60°.

A Continuously Tunable Miniaturized Patch Antenna

A tunable miniaturized patch antenna is introduced. Miniaturization is achieved by placing a layer of complementary split-ring resonators horizontally between the radiating patch and the ground plane. Tuning is implemented by detouring the current flow on the additional layer through a lumped capacitor or varactor, thereby shifting the resonant frequency. The result is a miniaturized antenna that is compact, easily fabricated, and tunable across a useful band. A measured prototype demonstrates a tuning range of 2-2.45 GHz while maintaining an area no larger than 1/9 of a traditional patch antenna.

Dynamic Beam Shaping Using a Dual-Band Electronically Tunable Reflectarray Antenna

An electronically reconfigurable dual-band reflectarray antenna is presented in this paper. The tunable unit cell, a ring loaded square patch with a single varactor diode connected across the gap between the ring and the patch, is modeled using both a full-wave solver and an equivalent circuit. The parameters of the equivalent circuit are calculated independently of the simulation and experiment using analysis techniques employed in frequency-selective surfaces (FSSs). The reflection phase of the proposed unit cell is shown to provide an excellent phase range of 335° in F-band and 340° in S -band. Results from the analysis are used to design and build a 10 × 10 element reflectarray antenna. The high tuning phase range of each element allows the fabricated reflectarray to demonstrate a very broad steering range of up to ± 60° in both frequency bands.

A Tunable Dual-Band Miniaturized Monopole Antenna for Compact Wireless Devices

A technique for producing miniaturized tunable planar monopole antennas for wireless communication applications is introduced. Miniaturization is achieved by optimizing the geometry of a pixelated metallic patch surrounding the monopole antenna. Tuning of the antenna is implemented by varying the capacitance of a varactor diode loaded between the pixelated metallic patch and the ground plane. The result is an ultra-compact, dual band, folded monopole antenna that fits into a hemisphere of radius λ0/20 at 2.1 GHz. Varying the capacitance of the varactor diode enables the two resonance frequencies to be tuned simultaneously, covering multiple frequency bands for different wireless applications. A prototype antenna has been fabricated and measured, confirming the feasibility of the proposed design.

Characterization of Biaxial Anisotropic Material Using a Reduced Aperture Waveguide

A technique is introduced for measuring the electromagnetic properties of a biaxial anisotropic material sample using a reduced-aperture waveguide sample holder designed to accommodate a cubical sample. All the tensor material parameters can be determined by measuring the reflection and transmission coefficients of a single sample placed into several orientations. The theoretical reflection and transmission coefficients necessary to perform the material parameter extraction are obtained using a modal analysis technique. An optimization method that seeks to minimize the difference between theoretically computed and measured reflection and transmission coefficients is used to perform the extraction. Measurements of a stacked dielectric medium is characterized to demonstrate feasibility of the reduced-aperture waveguide approach.

A dual-band tunable reflectarray

In this work, a dual-band reflectarray with reconfigurable beam angle is presented. The unit cell of the reflectarray is a square ring-patch structure which was optimized to perform within two distinct frequency bands. The full wave simulation software HFSS was used to analyze a unit cell inside a waveguide, approximating the infinite array scenario. The tuning of the unit cell was achieved by altering the capacitance of a varactor diode placed between the square ring and the patch. A 10 × 10 element array will be built and measured to demonstrate its capability of beam steering over a wide range of angles.

A Waveguide Verification Standard Design Procedure for the Microwave Characterization of Magnetic Materials

A waveguide standard is introduced for validation purposes on the measurement accuracy of electric and magnetic properties of materials at microwave frequencies. The standard acts as a surrogate material with both electric and magnetic properties and is useful for verifying systems designed to characterize engineered materials using the Nicolson-Ross-Weir technique. A genetic algorithm is used to optimize the all-metallic structure to produce a surrogate with both relative permittivity and permeability within a target range across S-band. A mode-matching approach allows the user to predict the material properties with high accuracy, and thus compensate for differences in geometry due to loose fabrication tolerances or limited availability of component parts. The mode-matching method also allows the user to design standards that may be used within other measurement bands. An example standard is characterized experimentally, the errors due to uncertainties in measured dimensions and to experimental repeatability are explored, and the usefulness of the standard as a verification tool is validated.

A microwave tomography system using a tunable mirror for beam steering

Microwave tomography is a fast-growing technique in the fields of NDE and medical industry. This paper presents a new microwave tomography system which reduces the complexities of conventional microwave imaging systems by utilizing a reconfigurable mirror, a tunable reflectarray antenna. In order to build a tunable reflectarray with beam steering capabilities, the unit cell characteristics should dynamically alter. Modelling and experimental results of a single unit cell are presented in this work.

Characterization of Y-Bias Ferrite Materials for Tunable Antenna Applications Using a Partially Filled Rectangular Waveguide

A methodology for measuring the constitutive parameters of a ferrite material is presented. This method can be used to assist the prediction of the properties of tunable antennas that use ferrite material as a substrate or tuning component. A nontraditional characterization method is required due to the general unavailability of samples of a sufficient size to fill the entire cross sections of waveguides appropriate for lower frequencies where gyromagnetic properties are most pronounced, and the difficulty of predicting or approximating the applied bias magnetic field. The proposed method overcomes the limitation of sample size by requiring only partial filling of a rectangular waveguide. It overcomes a lack of knowledge of the bias field by including the field as an unknown to be determined by the extraction process. The required theoretical reflection and transmission coefficients of the partially filled waveguide are determined using a mode-matching technique. A nonlinear least squares method is employed to extract the gyromagnetic material parameters and the bias field using optimization algorithms in MATLAB. The extracted parameters of a representative commercial ferrite obtained from multiple experimental configurations are compared with the values provided by the sample manufacturer to demonstrate the feasibility of this technique.