Touseef Hayat

This article presents highly radio-frequency (RF) transparent phase gradient synthetic metasurfaces made of sub-wavelength-sized 3D printable meta-atoms with tailored permittivity that cannot be achieved with off-the-shelf, commercially available materials. The synthesized meta-atoms design uses one dielectric block of PREPERM® ABS 1000 material with air and metallic inclusions to make low-and high-permittivity materials. The inclusions’ size and height are varied to achieve a complete phase range from 0 to 360∘, while maintaining transmission magnitudes greater than -3.0 dB. A two-dimensional array of meta-atoms forms a metasurface, which can be used for phase-shifting structures. Such metasurfaces can manipulate RF waves by introducing progressive phase delay into array elements. The proposed meta-atoms are employed to create highly RF transparent phase-gradient metal-dielectric composite metasurfaces (MDCMs) operating at 11 GHz. These MDCMs can be implemented through 3D printed technology using low-cost thermoplastics or polymers with composite filaments and minimal human intervention. A pair of MDCMs are combined with an array of microstrip patches to demonstrate 2D beam steering functionality numerically. The antenna system provides a peak directivity of 19.9 dBi with a maximum conical scanning angle of 114∘ and a directivity variation of less than 3 dB.

This article presents mechanically robust, low-cost, lightweight, and polarization-independent metallic metasurfaces (MMs) to enhance the gain and directivity of shortened horn antennas. The MM was designed based on the strategy of correcting the actual phase errors probed on the aperture of the horn using the near-field phase-transformation principle. The fundamental unit cell of the MM is made of a pair of cross slots created in a monolithic thin conductive sheet and is entirely free from high-cost dielectrics. The lack of dielectrics makes MM lightweight, cost-efficient and easy to fabricate the prototype for mass production. The MM has a 2D array of unit cells arranged to increase the gain of the shortened horn by improving aperture efficiency through local phase transformation in a wide frequency band. The concept is demonstrated by designing MMs for shortened horns with different heights and the same physical aperture at the center operating frequency of 12.5 GHz. The maximum gain-bandwidth with MM is achieved for the shortest horn, which is validated by measuring the physical prototype. The results indicate that horn gain with MM increases by 9.2 dB (from 11.1 to 20.3 dBi) and has a 3-dB fractional gain-bandwidth of 10.4%. The weighted density of the fabricated MM is only 0.87 g/cm ² . Including MM, the total antenna height is around 61% shorter than a conventional air-filled horn having a similar peak gain.

In the near-field meta-steering method, the near electric-field phase distribution is dynamically altered by rotating a pair of phase-gradient metasurfaces that are typically made out of dielectric lattices or metal patterns printed on bonded dielectric substrates. As a lightweight alternate, a new class of fully metallic metasurfaces (MMs) is proposed in this paper. The lack of dielectrics not only substantially reduces the cost and weight but also increases its potential in space and high-power applications. More importantly, the new metallic metasurfaces are designed such that they can be made by cutting narrow slots in fully planar thin metal sheets, retaining structural rigidity while reducing the complexity, cost and weight. The same MM works for any polarization. Each cell in the new MMs has close to ideal phase shift and transmission magnitude greater than –0.9 dB. A prototype was designed and fabricated to validate this MM-based beam-steering concept in the Ku-band. The maximum measured steering range in zenith is ±42°, with a full 360° steering in the azimuth. The measured 3-dB gain bandwidth is 700–800 MHz (5.6–6.4%), and the measured gain variation (scan loss) when steering over the whole range is 2.2–4.5 dB. The weight density and thickness of each MM are 0.88 g/cm² and 0.8λ₀, respectively. Including the feed, the total antenna height is 4.9λ₀.

The paper presents a method to design beam-steering antennas using a pair of 3D printed perforated dielectric structures (PDSs) placed in the near-field region of a base antenna, which has a fixed beam. Detailed designs and quantitative comparison of two beam-steering antenna systems are presented. One antenna system has a conical horn antenna and the other uses a resonant-cavity antenna (RCA) as the base antenna. In both cases, the first PDS transforms the phase distribution of the aperture near field and hence tilts the antenna beam to an offset angle. The second PDS, placed above the first, introduces an additional linear progression to the phase of the near field. The two PDSs are rotated independently to steer the beam in both azimuth and elevation. The PDSs have been 3D-printed using acrylonitrile butadiene styrene (ABS) filaments. Each prototype was fabricated in about 16 hours, weighs 300 grams, and costs approximately 5.5 US Dollars. The measured results show that, at the operating frequency of 11 GHz, the RCA-based system has a peak gain of 17.7 dBi compared to the 16.6 dBi gain obtained with the horn-based system. In a fixed E-plane, the variation in the aperture near-field phase of the horn antenna (115°) is much less than that of the RCA (360°). This reduces the efforts required for phase correction and hence led to the former having a larger 3dB measured gain bandwidth of 1.2 GHz compared with the 0.7 GHz bandwidth of the latter, but at the cost of 35.6% increase in the total height of the antenna system.

A 3D printed planar permittivity-gradient superstrate (PGS) is used to improve the directive radiation characteristics of a waveguide fed compact resonant-cavity antenna (C-RCA). Far-field directivity of classical uniform-superstrate based RCAs is limited due to non-uniform aperture phase distribution caused by even transmission through the superstrate. Transverse PGS has been used here to remarkably improve aperture phase distribution and hence directive radiation performance of RCAs. Furthermore, the PGS was rapidly prototyped in one hour and 43 minutes using a low cost acrylo-butadiene styrene (ABS) filament without using traditional multistep milling and machining. Single step fabrication was performed and effective dielectric constant of the ABS was varied through controlled infill percentage in different regions of the PGS. Measurements of a prototype indicate unrivaled results, from a smaller footprint, which includes peak directivity of 16.048 dB, 3dB directivity bandwidth of 49.65% and side lobe levels lower than -10.4 dB throughout the operating frequency band. The 3D printed PGS thus outperforms all previously reported superstrates, for RCAs, by demonstrating similar radiation performance with an equivalent material cost of only 0.41 USD.

A comparative analysis of two phase correcting structures (PCSs) is presented for an electromagnetic-bandgap resonator antenna (ERA). PCSs are made out of two distinct high and low permittivity materials i.e. Rogers O3010 and polylactic acid (PLA), respectively. Design and performance analysis is based on superstrate height profile, side-lobe levels, antenna directivity, aperture efficiency, prototyping technique and cost. Insertion loss for both superstrates is greater than 0.1 dB, assuring the maximum transmission of the antenna’s radiations through the PCSs. The presented study is based on full wave analysis used to integrate sections of superstrate with custom phase-delays, to attain nearly uniform phase at the output, resulting in improved radiation performance of antenna. The peak directivity of the ERA loaded with Rogers O3010 PCS has increased by 7.3 dB, which is 1.2 dB higher than that of PLA PCS. In addition, the height of the PCS made of Rogers is 71.3% smaller than the PLA PCS. However, the former will involve fabrication complexities related to machining compared to the latter which can be additively manufactured in single step.

Additively manufactured perforated superstrate (AMPS) is presented to realize directive radio frequency (RF) front-end antennas. The superstrate comprises spatially distributed dielectric unit-cell elements with square perforations, which creates a pre-defined transmission phase delay pattern in the propagating electric field. The proposed square perforation has superior transmission phase characteristics compared to traditionally machined circular perforations and full-wave simulations based parametric analysis has been performed to highlight this supremacy. The AMPS is used with a classical electromagnetic-bandgap resonator antenna (ERA) to improve its directive radiation characteristics. A prototype is developed using the most common, low-cost and easily accessible Acrylonitrile Butadiene Styrene (ABS) filament. The prototype was rapidly fabricated in less than five hours and weighs 139.3 g., which corresponds to the material cost of only 2.1 USD. The AMPS has remarkably improved the radiation performance of ERA by increasing its farfield directivity from 12.67 dB to 21.12 dB and reducing side-lobe level from -7.3 dB to -17.2 dB.

A method of designing low‐loss split‐ball resonator (SBR) for permittivity sensing and measurement at microwave frequencies using resonant perturbation technique is being presented. SBR geometry strengthens electric field in the capacitive region by confining greater resonant energy in the split. Enhanced sensitivity by virtue of potent electric field enabled us to sense and measure permittivity of common polar solvents (methanol and ethanol). Comparative analysis, eigenmode simulations, and empirical measurements exhibited improved sensitivity of SBR. The solution of Maxwell equations for boundary conditions before and after material perturbation produce expressions, which lead to permittivity evaluation.