Mingguang Tuo

3D Printed Dielectric Reflectarrays: Low-Cost High-Gain Antennas at Sub-Millimeter Waves

Dielectric reflectarray antennas are proposed as a promising low-loss and low-cost solution for high gain terahertz (THz) antennas. Variable height dielectric elements are used in the reflectarray designs, which allow for the use of low dielectric-constant materials. Polymer-jetting 3-D printing technology is utilized to fabricate the antenna, which makes it possible to achieve rapid prototyping at a low-cost. Numerical and experimental results are presented for 3 different prototypes operating at 100 GHz, which show a good performance. Moreover the methodology proposed here is readily scalable, and with the current material and fabrication technology, designs up to 1.0 THz can be realized. This study reveals that the proposed design approach is well suited for low-cost high-gain THz antennas.

High gain dielectric reflectarray antennas for THz applications

Dielectric reflectarray antennas are studied in this paper as a possible low-loss and low-cost solution for high gain THz antennas. Variable height dielectric slabs are proposed for the reflectarray elements which allow for the use of low dielectric-constant materials for the design. A 3-D printing technology is utilized to fabricate the antenna, and both numerical and experimental results are presented for a prototype operating at 100 GHz. This study shows that the proposed design approach is well suited for high gain THz antennas.

Design of a high-efficiency rectenna for 1.575 GHz wireless low power transmission

A 1.575 GHz rectenna has been developed for low input power operation. The rectenna incorporates a high efficiency, electrically small, metamaterial-inspired near field resonant parasitic antenna, and a Schottky diode that has a low built-in voltage, and a resistor as the load. The rectenna was analyzed with the Harmonic Balance method provided by the Advanced Design System (ADS). The measurement results show that the output efficiency of the rectenna with the resistive load is 34.1% and the voltage across the resistor is 0.73 V when the power delivered to the antenna is 1.0 mW (0.0 dBm). The predicted and measured results are in reasonable agreement.

Dual-Mode Substrate Integrated Waveguide Filter With Flexible Response

This paper proposes a novel dual-mode substrate integrated waveguide (SIW) filter technique. Based on the conventional dual-mode SIW structure, further investigation is performed. Multiple transmission zeros can be obtained at one side or both sides of the passband for an SIW cavity. Therefore, flexible design and high performance response can be available for dual-mode SIW filter. A dual-mode SIW bandpass filter with quasi-elliptic response and a dual-mode SIW diplexer with asymmetric channel response are simulated, fabricated, and measured to demonstrate and verify the novel property.

Nonlinear Microwave Characterization of CVD Grown Graphene

Linear and nonlinear microwave properties of chemical vapor deposition (CVD)-grown graphene are characterized by incorporating a coplanar waveguide (CPW) transmission-line test structure. The intrinsic linear transport properties (S-parameters) of the graphene sample are measured and extracted via a deembedding procedure and then fitted with an equivalent circuit model up to 10 GHz. A statistical uncertainty analysis based on multiple measurements is implemented to estimate the error of the extracted graphene linear parameters as well. Nonlinear properties (second- and third-order harmonics as a function of fundamental input power) of the sample are also measured with a fundamental input signal of 1 GHz. Clear harmonics generated from graphene are observed, while no obvious fundamental power saturation is seen. The measured nonlinearity is applied in a graphene patch antenna case study to understand its influence on potential applications in terms of third-order intermodulation levels.

Numerical analysis of terahertz generation characteristics of photoconductive antenna

A numerical model of terahertz (THz) photoconductive antenna (PCA) is developed and studied. This model includes the multi-physical phenomena of the PCA involving the light-matter interaction, photo-excited carrier dynamics and EM propagation of the generated THz radiation. Both in-house finite-difference-time-domain (FDTD) method and commercial tools such as COMSOL are used in this study. Various PCA-related parameters, such as the pump laser power, DC bias voltage, laser pulse width, and beam spot location, as well as material related parameters (e.g., carrier lifetime, mobility and doping density) can be investigated using this model.

Comparison of photoconductive antenna performance on LT-GaAs and SI-GaAs substrates

In this work, butterfly shaped photoconductive antennas (PCAs) on low-temperature grown (LT) GaAs and semi-insulating (SI) GaAs substrate as terahertz (THz) emitters are experimentally characterized and compared. Dependences of the THz radiated field on the applied DC bias voltage and laser pump power are compared. Quadratic DC bias dependence is seen for SI-GaAs PCA compared to a linear dependence for LT-GaAs PCA. Scaling rule can be applied to the laser power dependence to fit the measurement data and the saturation can be attributed to the screening effect. Studies of material property influence on THz radiated power allow exploration of ways to enhance PCA performance.

Characterization of anisotropic conduction of horizontally aligned carbon nanotube thin films

In this paper, the anisotropic conductivities of Horizontally Aligned Carbon Nanotube (HACNT) thin film are characterized using Vector Network Analyzer (VNA) and four-probe technique. For microwave (X-band), the transmission experiments are performed in a waveguide setup and the conductivities of HACNT thin film are extracted using the uniform field approximation. For two CNTs orientation directions, the results are about 1000 S/m and 3000 S/m, respectively. The DC conductivities are measured using the four-probe method. The average conductivities are 1360 S/m and 1903 S/m, respectively. These results confirm the anisotropic conduction of HACNT thin film.

Microwave properties of suspended single-walled carbon nanotubes with a field-effect transistor configuration

In this paper, microwave transmission properties of suspended single-walled carbon nanotubes (SWCNTs) have been investigated up to 7.1 GHz with a field-effect transistor (FET) configuration by measuring the two-port S-parameters under different gate bias voltages. An open-through de-embedding method has been used to extract the intrinsic properties of CNTs. A lumped-element equivalent circuit model has been used and the values of each component have been fitted as a function of gate bias voltage.

Contribution assessment of antenna structure and in-gap photocurrent in terahertz radiation of photoconductive antenna

Photoconductive antenna (PCA) is one of the most widely used terahertz (THz) devices nowadays. Although PCAs have been extensively studied through both theoretical analysis and device design, there still lacks a common agreement upon the mechanism of THz radiation. One of the central questions is how to distinguish and assess the contribution of the antenna structure and in-gap photocurrent to the overall radiation of a PCA. In this work, a three-dimensional full-wave model was first used to quantify the overall far-field radiation of PCAs. The commercial solver (i.e., HFSS) and the Hertzian dipole approximation method were then applied to quantify the far-field radiation solely from the antenna structure and in-gap photocurrent, respectively. The contribution of the antenna structure and in-gap photocurrent can therefore be distinguished by comparing the simulation results among the three methods. The results suggest that, although the THz radiation originates from laser-excited photocurrent within the gap, the overall THz radiation of a PCA is predominated by the antenna structure. As a validation, the cancellation effect was predicated by numerical simulation of coplanar stripline PCA and confirmed with experiment using butterfly shaped stripline PCA. The presented work uncovers the details of the underlying radiation mechanism of the PCA. This could inspire PCA design that aims for engineering the radiation properties of a PCA for specific applications.Photoconductive antenna (PCA) is one of the most widely used terahertz (THz) devices nowadays. Although PCAs have been extensively studied through both theoretical analysis and device design, there still lacks a common agreement upon the mechanism of THz radiation. One of the central questions is how to distinguish and assess the contribution of the antenna structure and in-gap photocurrent to the overall radiation of a PCA. In this work, a three-dimensional full-wave model was first used to quantify the overall far-field radiation of PCAs. The commercial solver (i.e., HFSS) and the Hertzian dipole approximation method were then applied to quantify the far-field radiation solely from the antenna structure and in-gap photocurrent, respectively. The contribution of the antenna structure and in-gap photocurrent can therefore be distinguished by comparing the simulation results among the three methods. The results suggest that, although the THz radiation originates from laser-excited photocurrent within the g...