This paper will review the evolution of wearable textile antennas over the last couple of decades. Particular emphasis will be given to the process of embroidery. This technique is advantageous for the following reasons: (i) bespoke or mass produced designs can be manufactured using digitized embroidery machines; (ii) glue is not required and (iii) the designs are aesthetic and are integrated into clothing rather than being attached to it. The embroidery technique will be compared to alternative manufacturing processes. The challenges facing the industrial and public acceptance of this technology will be assessed. Hence, the key opportunities will be highlighted.

The paper presents the designs of ultra-wideband microwave flat gradient index (GRIN) lenses, which realizes over a 108% fractional bandwidth (12 - 40 GHz). The frequency-independent ray optics method is employed to determine the radially varying permittivity profile of the lenses. The challenge of realizing such a radially varying profile, and the limitations in dielectric material choices, are overcome by two additive-manufacturing-aided approaches: (i) partially infilled dielectrics with a varied periodicity, which ensures the lens performance at the higher end of the frequency range; and (ii) artificially engineered dielectrics (AED) with sub-wavelength-scale metallic inclusions, which enables high permittivity dielectrics and leads to benefits of thickness and mass reduction for the GRIN lenses. Measured results demonstrate that the GRIN lenses improve the gain of open-ended waveguide sources by 8.7 to 15.6 dB over a wide frequency range from 12 to 40 GHz, with the realized gain of up to 23.6 dBi. Both the simulation and measurements of the presented design confirm the potential of implementing the proposed GRIN lens design in high directivity and beamforming antenna applications, across an ultra-wideband frequency range.

This is a review article of the latest advances in 3D printing for enabling new materials and new geometries for radio-frequency (RF) devices, antennas, and metamaterials. The article discusses the achievable material properties and various optimized applications that are achievable by creating new shapes in either dielectric or metal. This article demonstrates what is currently possible with additive manufacturing and the current limitations. Various additively manufactured RF devices are reviewed.

This letter presents dielectric properties of air filled synthetic substrates fabricated in a single process using three‐dimensional printing. The permittivity and loss tangent of a given sized substrate can be changed by controlling the air infill volume fraction. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2344–2346, 2015

Fused filament fabrication (FFF) is a well-known and greatly accessible additive manufacturing technology, that has found great use in the prototyping and manufacture of radiofrequency componentry, by using a range of composite thermoplastic materials that possess superior properties, when compared to standard materials for 3D printing. However, due to their nature and synthesis, they are often a great challenge to print successfully which in turn affects their microwave properties. Hence, determining the optimum printing strategy and settings is important to advance this area. The manufacturing study presented in this paper shows the impact of the main process parameters: printing speed, hatch spacing, layer height and material infill, during 3D printing on the relative permittivity (ε_r), and loss tangent (tanδ) of the resultant additively manufactured test samples. A combination of process parameters arising from this study, allowed successful 3D printing of test samples, that marked a relative permittivity of 9.06 ± 0.09 and dielectric loss of 0.032 ± 0.003.

A broadband dual circularly polarized (dual-CP) reflectarray based on 3-D printed dielectric materials is proposed in this article. A novel 3-D dielectric array element that enables the broadband linearly polarization (LP) to CP transformation is proposed. The unit cell consists of two orthogonal dielectric cuboids that adjust the phases of the two orthogonal LP waves independently and then combine them into a CP wave. The innovative unit cell design provides an extra degree of freedom in varying the geometries of the array elements in all three dimensions, which enables us to independently control the phases of the two LP waves. This maintains an equal amplitude and 90° phase difference condition across the entire reflectarray surface, realizing a broadband and high gain LP–CP reflectarray. The placement of the feed is also optimized to achieve the highest aperture efficiency. Finally, an off-set reflectarray was designed and fabricated using lost-cost 3-D printing. The reflectarray is able to provide both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), with just an LP feed. The measurements agree well with simulated results where the maximum realized gain and directivity at 34 GHz are measured as 27.9 and 28.1 dBi, respectively. The measured 3 dB gain bandwidth and aperture efficiency are 30% and up to 38%, respectively. More importantly, a broad 3 dB axial ratio (AR) bandwidth greater than 40% has been achieved for both LHCP and RHCP, covering almost the entire frequency band of interest, ranging from 26 to 40 GHz.