Reconfigurable Antennas

In this new book, we present a collection of the advanced developments in reconfigurable antennas and metasurfaces. It begins with a review of reconfigurability technologies, and proceeds to the presentation of a series of reconfigurable antennas, UWB MIMO antennas and reconfigurable arrays. Then, reconfigurable metasurfaces are introduced and the latest advances are presented and discussed

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

A Low-Profile Frequency Reconfigurable Grid-Slotted Patch Antenna

This paper presents a novel low-profile high gain frequency reconfigurable patch antenna with unidirectional radiation pattern by using a grid-slotted patch with tunable varactors loading. The antenna consists of two stacked substrates and three metal layers. A grid-slotted patch with two tunable varactors is placed on the top layer, a microstrip line is placed in the middle of two substrates, and the ground plane is on the bottom layer. A single dc voltage applied on two varactors is used to control the working frequencies of the proposed antenna. By altering the bias voltage, the working frequency of the proposed antenna can be continuously changed within a wide range from 2.45 to 3.55 GHz. The antenna maintains broadside radiation and stable radiation pattern in all the operating modes. The measured antenna gain of the proposed antenna rises from 4.25 to 8.49 dBi with the working frequency increases from 2.45 to 3.55 GHz. Compared to other frequency-reconfigurable antennas available in the literature, the proposed antenna has advantages of a wide frequency tuning range over a bandwidth of 1.45:1, high frequency selectivity, low profile (0.016 free-space wavelength at 2.45 GHz), high gain, stable unidirectional pattern, simple structure, and low cost. These advantages make it a promising candidate for cognitive radio and future wireless communication system

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Photonic controlled metasurface for intelligent antenna beam steering applications including 6G mobile communication systems

This paper presents a novel metasurface antenna whose radiation characteristics can be remotely controlled by optical means using PIN photodiodes. The proposed reconfigurable antenna is implemented using a single radiating element to minimize the size and complexity. The antenna is shown to exhibit a large impedance bandwidth and is capable of radiating energy in a specified direction. The proposed antenna consists of a standard rectangular patch on which is embedded an H-tree shaped fractal slot of order 3. The fractal slot is used to effectively reduce the physical size of the patch by 75 % and to enhance its impedance bandwidth. A metasurface layer is strategically placed above the patch radiator with a narrow air gap between the two. The metasurface layer is a lattice pattern of square framed rhombus ring shaped unit-cells that are interconnected by PIN photodiodes. The metasurface layer essentially acts like a superstrate when exposed to RF/microwave radiation. Placed below the patch antenna is a conductive layer that acts like a reflector to enhance the front-toback ratio by blocking radiation from the backside of the patch radiator. The patch’s main beam can be precisely controlled by photonically illuminating the metasurface layer. The antenna’s performance was modelled and analyzed with a commercial 3D electromagnetic solver. The antenna was fabricated on a standard dielectric substrate FR4 and has dimensions of 0.778λo × 0.778λo × 0.25λo mm3 , where λo is the wavelength of free space centered at 1.35 GHz. Measured results confirm the antenna’s performance. The antenna exhibits a wide fractional band of 55.5 % from 0.978 to 1.73 GHz for reflection-coefficient (S11) better than − 10 dB. It has a maximum gain of 9 dBi at 1.35 GHz with a maximum front-to-back ratio (F/B) of 21 dBi. The main beam can be steered in the elevation plane from − 24◦ to +24◦. The advantage of the proposed antenna is it does not require any mechanical movements or complicated electronic systems.Dr. Mohammad Alibakhshikenari acknowledges support from the CONEX-Plus programme funded by Universidad Carlos III de Madrid and the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 801538. The authors also sincerely appreciate funding from Researchers Supporting Project number (RSP2023R58), King Saud University, Riyadh, Saudi Arabia. Additionally, this work was supported by Ministerio de Ciencia, Innovación y Universidades, Gobierno de España (Agencia Estatal de Investigación, Fondo Europeo de Desarrollo Regional -FEDER-, European Union) under the research grant PID2021-127409OB-C31 CONDOR. Besides above, the Article Processing Charge (APC) was afforded by Universidad Carlos III de Madrid (Read & Publish Agreement CRUE-CSIC 2023)

Dissipative Materials Enabled Subwavelength Nanophotonics

Properly structuring materials at subwavelength scale allows for strong light-matter interaction, thereby enhancing near-field effects and engineering far-field scattering through intermodal interference. A majority of such effects are associated with plasmonics where electromagnetic waves created in the vicinity of metallic nanostructures is able to give rise to a variety of novel phenomena and fascinating applications. In the recent years, dielectric nanoparticles with high refractive index based on optically induced electric and magnetic Mie resonances attract a plethora of attention. In this rapidly developing field, dissipative loss in optical materials is considered one of the major challenges. Here, in this dissertation, we show that, counter-intuitively, it contributes positively to sub-wavelength scale light enhancement and confinement, and also improves scattering efficiency in the far field. In the first part of this dissertation, near field enhancement in dissipative dielectric antennas is demonstrated to be orders of magnitude higher than their lossless dielectric counterparts, which is particularly favorable in deep UV applications where metals are plasmonically inactive and transparent dielectrics always have low index. The loss facilitated field enhancement is the result of large material permittivity contrast and electric field discontinuity. These dissipative dielectric nanostructures can be easily achieved with a great variety of dielectrics at their Lorentz oscillation frequencies, thus having the potential to build a completely new material platform boosting light-matter interaction over broader frequency ranges, with advantages such as bio-compatibility, CMOS compatibility and harsh environment endurance. Additionally, manipulation of ultra-violet light through metasurface in the far field utilizing the silicon loss is then presented. We experimentally demonstrate Si metasurfaces working effectively over a broad band down to 290nm, with efficiencies comparable to plasmonic metasurface performance in the infrared regime. And for the first time, we show photolithography enabled by metasurface-generated ultraviolet holograms. We attribute such performance enhancement to the large scattering cross-sections of Si antennas in the ultraviolet range, which is adequately modeled via a circuit model. Our new platform will deepen our understanding of the role of material dissipation and introduce even more material options to broadband metaphotonic applications, including those in integrated photonics and holographic lithography technologies.Dynamically tunable far field with subwavlength nanostructures is always desired for practical applications. In the last section of this dissertation, we introduce a lithography free and field-programmable photonic metacanvas. Previous attempts of realizing such idea used micro-mechanical metamaterials or amorphous-crystalline phase transition materials, which are limited in terms of the functionalities, efficiency, cost, and high working temperature (> 600oC). It is much desired to reconfigure photonic devices in a fast, large-scale, cost-effective, reliable, and free-style way at or near room temperature. Here, we present a completely rewritable meta-canvas on which arbitrary photonic devices can be rapidly written, erased and rewritten. The writing is with a low-power (1 mW) continuous laser and the entire process stays below ~ 90oC. Using these devices we demonstrate dynamical manipulation of optical waves for light propagation, reconstruction and polarization. Such meta-canvas supports physical (re)compilation of photonic operators akin to that of FPGA, opening up possibilities where a single photonic element can be field-programmed to deliver complex, system-level functionalities

Time-varying Huygens' meta-devices for parametric waves

Huygens' metasurfaces have demonstrated almost arbitrary control over the shape of a scattered beam, however, its spatial profile is typically fixed at fabrication time. Dynamic reconfiguration of this beam profile with tunable elements remains challenging, due to the need to maintain the Huygens' condition across the tuning range. In this work, we experimentally demonstrate that a time-varying metadevice which performs frequency conversion can steer transmitted or reflected beams in an almost arbitrary manner, with fully dynamic control. Our time-varying Huygens' metadevice is made of both electric and magnetic meta-atoms with independently controlled modulation, and the phase of this modulation is imprinted on the scattered parametric waves, controlling their shapes and directions. We develop a theory which shows how the scattering directionality, phase and conversion efficiency of sidebands can be manipulated almost arbitrarily. We demonstrate novel effects including all-angle beam steering and frequency-multiplexed functionalities at microwave frequencies around 4 GHz, using varactor diodes as tunable elements. We believe that the concept can be extended to other frequency bands, enabling metasurfaces with arbitrary phase pattern that can be dynamically tuned over the complete 2\pi range

Miniaturized Microwave Devices and Antennas for Wearable, Implantable and Wireless Applications

This thesis presents a number of microwave devices and antennas that maintain high operational efficiency and are compact in size at the same time. One goal of this thesis is to address several miniaturization challenges of antennas and microwave components by using the theoretical principles of metamaterials, Metasurface coupling resonators and stacked radiators, in combination with the elementary antenna and transmission line theory. While innovating novel solutions, standards and specifications of next generation wireless and bio-medical applications were considered to ensure advancement in the respective scientific fields. Compact reconfigurable phase-shifter and a microwave cross-over based on negative-refractive-index transmission-line (NRI-TL) materialist unit cells is presented. A Metasurface based wearable sensor architecture is proposed, containing an electromagnetic band-gap (EBG) structure backed monopole antenna for off-body communication and a fork shaped antenna for efficient radiation towards the human body. A fully parametrized solution for an implantable antenna is proposed using metallic coated stacked substrate layers. Challenges and possible solutions for off-body, on-body, through-body and across-body communication have been investigated with an aid of computationally extensive simulations and experimental verification. Next, miniaturization and implementation of a UWB antenna along with an analytical model to predict the resonance is presented. Lastly, several miniaturized rectifiers designed specifically for efficient wireless power transfer are proposed, experimentally verified, and discussed. The study answered several research questions of applied electromagnetic in the field of bio-medicine and wireless communication.Comment: A thesis submitted for the degree of Ph