Xiaoju Yu

Mechanical, Electromagnetic, and X-ray Shielding Characterization of a 3D Printable Tungsten–Polycarbonate Polymer Matrix Composite for Space-Based Applications

Material-extrusion three-dimensional (3D) printing has recently attracted much interest because of its process flexibility, rapid response to design alterations, and ability to create structures “on-the-go”. For this reason, 3D printing has possible applications in rapid creation of space-based devices, for example cube satellites (CubeSat). This work focused on fabrication and characterization of tungsten-doped polycarbonate polymer matrix composites specifically designed for x-ray radiation-shielding applications. The polycarbonate–tungsten polymer composite obtained intentionally utilizes low loading levels to provide x-ray shielding while limiting effects on other properties of the material, for example weight, electromagnetic functionality, and mechanical strength. The fabrication process, from tungsten functionalization to filament extrusion and material characterization, is described, including printability, determination of x-ray attenuation, tensile strength, impact resistance, and gigahertz permittivity, and failure analysis. The proposed materials are uniquely advantageous when implemented in 3D printed structures, because even a small volume fraction of tungsten has been shown to substantially alter the properties of the resulting composite.

3D printed multilayer microstrip line structure with vertical transition toward integrated systems

In this paper, a 3D printed multilayer microstrip line structure with vertical transition is designed, fabricated and characterized. The dielectric part of the structure is printed using the FDM method and the conductor part is printed using the ultrasonic wire embedding approach. The measured total insertion loss of the 3D printed multilayer microstrip (90 mm long) including the vertical transition is smaller than 2 dB below 6 GHz. The measured results agree well with the simulation. The performance of this structure demonstrates that 3D printing techniques may be able to realize functional multilayer RF components / systems. As an example, a 3D printed multilayer phased array is designed based on similiar microstrip and vertical transition structure in this work. The simulated results show good impedance matching around 3.5GHz and a high directive beam at expected direction.

Direction of arrival estimation using Luneburg lens

In this paper, a 3-D Luneburg Lens is employed for direction finding application. Using the special property of a Luneburg lens that every point on the surface of the Lens is the focal point of a plane wave incident from the opposite side, a number of detectors are mounted around the surface of the lens to estimate the direction of arrival (DOA) of a microwave signal. To demonstrate the proposed direction finding system, a Luneburg lens with five detectors mounted on its surface to receive the signal from −20° to 20° is measured at 5.6 GHz. The initial direction finding results using a correlation algorithm show that the estimated error is smaller than 2° within −15° to 15° incident angles.

Broadband electronically beam scanning structure using Luneburg lens

A novel broadband electronically beam scanning structure based on Luneburg lens phased array is investigated in this paper. The radiation elements of the phased array are mounted on the surface of a Luneburg lens. Without amplitude and phase control of the elements, only discrete scanning angles are available. In this paper, beam scanning to arbitrary angle is demonstrated by fully controlling the amplitude and phase. Compare to conventional phased array beam scanning system, the proposed structure has no scan angle coverage limit and has a broadband working frequency. Also, due to the symmetry of Luneburg lens, no beam shape variation would occur during angle scanning. Moreover, this structure requires much less system complexity to achieve a highly directional beam and therefore the cost of this system could be much lower than conventional phased array.

A Microwave Direction of Arrival Estimation Technique Using a Single Antenna

A direction of arrival (DoA) estimation technique for broadband microwave signals is proposed using a single ultrawideband antenna. It is inspired by the sound source localization ability of a human auditory system using just one ear (monaural localization). By exploiting the incident angle-dependent frequency response of a wideband antenna, the DoA of a broadband microwave signal can be estimated. The DoA estimation accuracies are evaluated for two antenna configurations and microwave signals with different signal-to-noise ratios. Encouraging the DoA estimation performance of the proposed technique is demonstrated in both simulation and experiment.

Electromagnetic materials of artificially controlled properties for 3D printing applications

In this paper, a polymer matrix composite method by mixing printable polymer with a number of possible nanoparticles is investigated to achieve artificially controlled effective electromagnetic properties for 3D additive manufacturing applications. The material properties are evaluated using effective medium theory. The results show that this method can achieve robust electromagnetic property control with various nanoparticle fillings.

Direction of arrival estimation utilizing incident angle dependent spectra

Inspired by monaural (one ear) sound localization ability of human auditory system, a novel direction of arrival (DoA) technique for pulse based broadband microwave signals is proposed. A microstrip leaky wave antenna as the receiving component is designed and then fabricated with good matching and reasonable radiation efficiency in the interested frequency range. By exploiting the incident angle dependent frequency response of the receiving antenna, the DoA of a broadband microwave signal can be estimated with high accuracy. Good DoA performance within 90° range of the proposed technique is demonstrated in both simulation and experiment.

Antenna radiation pattern control through 3D printed inhomogeneous dielectrics

Inhomogeneous dielectrics can be used as antennas or to control antenna radiation patterns. For instance, Luneburg lens antennas have the refractive index distribution of n(r)= [2 − (r/a)2]1/2. They can achieve one focus on its surface and the other focus at infinity. Inhomogeneous dielectrics can also be used to increase the gain and narrow the beam width of a horn antenna. Moreover, inhomogeneous dielectrics can be realized by a fast and economic manufacturing method, additive manufacturing (AM), which is also called 3D printing technology. It enables 3D fabrication of arbitrary shape and structure by printing layer by layer. By changing the mixing ratio of multiple 3D printing materials, spatially varying dielectric constants can be achieved.

Design of wideband unit-cell element for 5G antenna arrays

The previous generations of cellular networks are almost packed in the UHF band with a frequency range of 300 MHz-3 GHz in the radio spectrum. Recently, the Ka-band is under investigation to be commercially used in next generation of cellular systems, due to the spectrum availability and the small size of the components. The main purpose of this paper is to design a wideband antenna element at 28 GHz, so that it can be used in the antenna arrays of next generation mobile networks. The proposed unit-cell is a proximity coupled stacked patch antenna. The antenna parameters and characteristics are investigated both through simulation and measurement. The antenna achieves a measured gain of 7.1 dB at 28 GHz. The measured impedance bandwidth and 1-dB gain bandwidth are 34.48 % and 17.4 %, respectively.

Direction of arrival estimation enhancement for closely spaced electrically small antenna array

In this paper, compact direction finding systems using a scatterer of a high dielectric constant in between adjacent closely spaced electrically small antennas are examined. By adding a high-permittivity scatterer, the directional sensitivity can be enhanced. However, due to limited physical dimension, an electrically small antenna has highly reactive impedance. To enhance the received power level, a matching network is included. The highest directional sensitivity satisfying a given power constraint is compared for with and without scatterer cases. In addition, widely used matching approaches such as multiport-conjugate matching (MCM), self-conjugate matching (SCM), and eigenmode decoupling matching are investigated to increase the received power. The impact of these matching networks on the directional sensitivity is studied. The power and the directional-sensitivity bandwidth after matching are also analyzed. Finally, the two-monopole and a high-permittivity scatterer system with SCM and MCM circuits is fabricated and tested.