Kuiwen Xu

A Printed Single-Layer UWB Monopole Antenna With Extended Ground Plane Stubs

In this letter, a compact coplanar-waveguide-fed single-layer printed antenna with an ultrawideband (UWB) rectangular monopole radiator etched with a half-elliptical slot is presented. Collaborating with the UWB radiator, two symmetrical open-circuit stubs are extended from the ground plane to jointly achieve an ultrawideband impedance match with a compact size. The proposed antenna is fabricated and tested in an anechoic chamber, showing an ultrawide operating frequency range from 3.7 to 10.1 GHz with a quasi-omnidirectional gain from 2.0 to 7.3 dBi. With the advantages of a reduced size, an improved voltage standing wave ratio (VSWR), and a monolayer configuration without any back ground plane, the proposed antenna can be used in a wide range of UWB applications.

Towards Experimental Perfectly-Matched Layers With Ultra-Thin Metamaterial Surfaces

In this paper, we modify uniaxial perfectly matched layer to an entirely passive medium and demonstrate its experimental realization using a deep sub-wavelength metamaterial surface. The relative permittivity and permeability of the surface are matched, mostly imaginary-valued, and far greater than unity. These conditions allow the impedance of the metamaterial surface to be completely matched to air, and produce an extremely large internal dissipation, resulting in a 99.97% power absorption at normal incidence and within a layer thickness of about 1/40 of the free space wavelength.

Multiplicative-Regularized FFT Twofold Subspace-Based Optimization Method for Inverse Scattering Problems

In this paper, we combine two techniques together, i.e., the fast Fourier transform-twofold subspace-based optimization method (FFT-TSOM) and multiplicative regularization (MR) to solve inverse scattering problems. When applying MR to the objective function in the FFT-TSOM, the new method is referred to as MR-FFT-TSOM. In MR-FFT-TSOM, a new stable and effective strategy of regularization has been proposed. MR-FFT-TSOM inherits not only the advantages of the FFT-TSOM, i.e., lower computational complexity than the TSOM, better stability of the inversion procedure, and better robustness against noise compared with the SOM, but also the edge-preserving ability from the MR. In addition, a more relaxed condition of choosing the number of current bases being used in the optimization can be obtained compared with the FFT-TSOM. Particularly, MR-FFT-TSOM has even better robustness against noise compared with the FFT-TSOM and multiplicative regularized contrast source inversion (MR-CSI). Numerical simulations including both inversion of synthetic data and experimental data from the Fresnel data set validate the efficacy of the proposed algorithm.

Wideband Modeling and Characterization of Differential Through-Silicon Vias for 3-D ICs

This paper presents the wideband modeling and analysis of differential through-silicon vias (D-TSVs) in 3-D ICs. An equivalent-circuit model of the ground-signal-signal-ground-type D-TSVs is given and validated against a commercial full-wave electromagnetic simulation tool. The common- and differential-mode impedances are extracted using the partial-element equivalent-circuit method, while the admittances are calculated analytically, with the MOS effects considered and treated appropriately. The circuit model can also be used for studying the differential annular TSVs (ATSVs). It is shown that the ATSVs are more suitable for transmitting differential signals in comparison with the cylindrical TSVs. Based on the equivalent-circuit model, the characteristic impedances and the forward transmission coefficients of the D-TSVs made of Cu and carbon nanotubes are characterized and compared under different settings of frequencies and temperatures.

Emulating Anyonic Fractional Statistical Behavior in a Superconducting Quantum Circuit

Anyons are exotic quasiparticles obeying fractional statistics, whose behavior can be emulated in artificially designed spin systems. Here we present an experimental emulation of creating anyonic excitations in a superconducting circuit that consists of four qubits, achieved by dynamically generating the ground and excited states of the toric code model, i.e., four-qubit Greenberger-Horne-Zeilinger states. The anyonic braiding is implemented via single-qubit rotations: a phase shift of π related to braiding, the hallmark of Abelian 1/2 anyons, has been observed through a Ramsey-type interference measurement.

Joint quantum state tomography of an entangled qubit–resonator hybrid

The integration of superconducting qubits and resonators in one circuit offers a promising solution for quantum information processing (QIP), which also realizes the on-chip analogue of cavity quantum electrodynamics (QED), known as circuit QED. In most prototype circuit designs, qubits are active processing elements and resonators are peripherals. As resonators typically have better coherence performance and more accessible energy levels, it is proposed that the entangled qubit–resonator hybrid can be used as a processing element. To achieve such a goal, an accurate measurement of the hybrid is first necessary. Here we demonstrate a joint quantum state tomography (QST) technique to fully characterize an entangled qubit–resonator hybrid. We benchmarked our QST technique by generating and accurately characterizing multiple states, e.g. |gN〉 + |e(N − 1)〉 where (|g〉 and |e〉) are the ground and excited states of the qubit and (|0〉,...,|N〉) are Fock states of the resonator. We further provided a numerical method to improve the QST efficiency and measured the decoherence dynamics of the bipartite hybrid, witnessing dissipation coming from both the qubit and the N-photon Fock state. As such, the joint QST presents an important step toward actively using the qubit–resonator element for QIP in hybrid quantum devices and for studying circuit QED.

Power Synthesis at 110-GHz Frequency Based on Discrete Sources

Terahertz technology is one of the research fronts in the microwave society. Among many technical challenges, achieving high-power terahertz radiation has been attracting many efforts. In this paper, we investigate the possibility of power synthesis at low-end frequencies of the terahertz gap based on discrete sources. We show that by applying precision digital phase control, such a power synthesis can be achieved, overcoming the difficulty of phase alignment at these frequencies. For demonstration, we implement a 110-GHz prototype system employing solid-state impact avalanche and transit time diodes. Using a simulation- and measurement-based design methodology, the impedance matching of the designed cavity is able to be simultaneously obtained at both the RF bias and the 110-GHz frequency without using any absorbing material. Detailed design, simulation, and measurement of the prototype are introduced and the experimental results comply well with analytical expectations. Analysis shows that with increased wide digital bit width, the proposed approach is able to provide sufficient phase control precision, making it possible to be used in the power synthesis applications at low terahertz frequencies.

Analytical Beam Forming for Circularly Symmetric Conformal Apertures

In this paper, we present an analytical beam-forming approach capable of synthesizing differently shaped beams for circularly symmetric conformal apertures with axisymmetrical excitations. Closed form formulas of far-field radiation are mathematically derived in order to obtain rotationally symmetric radiation patterns for typical conformal apertures frequently used in satellite and flight vehicle applications, such as the cone-surfaced, truncated cone-surfaced, hybrid disc-cone and sphere-cone apertures. Based on these formulas, various shaped beams, including pencil, flat-topped and bimodal beams can be rapidly achieved by adjusting either the geometric parameters or the excitation distributions of the conformal apertures. The deterministic approach proposed in this paper provides an efficient method to synthesize specified beam shapes for the aforementioned conformal apertures. Collaborating with conventional optimization based beam forming approaches, the proposed approach can effectively shorten the time-consuming optimization in the beam forming of circularly symmetric conformal arrays, especially large conformal arrays.

Versatile Beam Forming With Concentric Excitations Based On Multiple Weighted Sinc or Bessel Function Distribution

In this paper, we propose a beam forming approach capable of synthesizing versatile, pre-specified beam shapes using concentric excitations satisfying multiple weighted sinc or Bessel function distribution. We show by both theoretical calculation and full wave simulation that by tuning different weights of a sinc or Bessel function distribution, not only radiation beams with pencil, flat-topped and bimodal shapes can be synthesized, but also the beam-width and the side lobe level can be independently adjusted. An example is provided to demonstrate how an isoflux beam aiming at a better coverage of the earth surface is synthesized, and how an optimized continuous distribution is properly discretized for a physical realization of a satellite aperture array antenna. The approach proposed in this paper can be applied to a wide range of applications that require performance optimization of concentric ring array antennas.

Microwave Imaging under Oblique Illumination

Microwave imaging based on inverse scattering problem has been attracting many interests in the microwave society. Among some major technical challenges, the ill-posed, multi-dimensional inversion algorithm and the complicated measurement setup are critical ones that prevent it from practical applications. In this paper, we experimentally investigate the performance of the subspace-based optimization method (SOM) for two-dimensional objects when it was applied to a setup designed for oblique incidence. Analytical, simulation, and experimental results show that, for 2D objects, neglecting the cross-polarization scattering will not cause a notable loss of information. Our method can be potentially used in practical imaging applications for 2D-like objects, such as human limbs.