Pixel Antenna Research Articles

Performance-constrained multi-objective optimization of antennas for miniaturization design

The miniaturization of antennas is crucial as it improves the integration of wireless communication system. In order to achieve miniaturization of antennas, a performance-constrained multi-objective optimization method (PCMOM) considering the size and return loss is proposed. In the PCMOM method, an optimization strategy based on a multi-port network model is introduced, enabling the formation of antennas with various structures. Furthermore, we integrate the constraint of return loss performance into the non-dominated sorting genetic algorithm II (NSGA-II), eliminating solutions that do not meet performance requirements. Three pixel antennas are designed using the PCMOM method and two of them are fabricated. Experimental results demonstrate that the proposed PCMOM method can effectively address the complex trade-off issues in antenna miniaturization design.

A Self-adapting Pixel Antenna - Substrate Lens System for Infrared Frequencies

In this work, we propose a concentrator lens - antenna arrangement, potentially suitable for infrared sensing and energy harvesting rectenna systems. The structure consists of a pixel antenna, self-adapting for the direction of the incident infrared radiation, and a concentrator lens, both optimized for the mid-infrared spectrum. The silicon substrate lens is situated above the pixel antenna, enabling the concentration of the incident light on the antenna; silicon was chosen due to its transparency in the IR spectrum. We examine how various parameters of the lens, in conjunction with the different states of the pixel antenna, affects the performance of the system. The simulations show that the gain of the arrangement increases considerably in correlation with the radius of the lens. The results suggest that the energy conversion efficiency of infrared rectenna systems can be enhanced by several orders of magnitude with the utilization of the proposed arrangement.

Reconfigurable Massive MIMO: Harnessing the Power of the Electromagnetic Domain for Enhanced Information Transfer

The capacity of commercial massive multiple-input multiple-output (mMIMO) systems is constrained by the limited array aperture at the base station, and cannot meet the everincreasing traffic demands of wireless networks. Given the array aperture, holographic MIMO with infinitesimal antenna spacing can maximize the capacity, but is physically unrealizable. As a promising alternative, reconfigurable mMIMO is proposed to harness the unexploited power of the electromagnetic (EM) domain for enhanced information transfer. Specifically, the reconfigurable pixel antenna technology provides each antenna with an adjustable EM radiation (EMR) pattern, introducing extra degrees of freedom for information transfer in the EM domain. In this article, we present the concept and benefits of availing the EMR domain for mMIMO transmission. Moreover, we propose a viable architecture for reconfigurable mMIMO systems, and the associated system model and downlink precoding are also discussed. In particular, a three-level precoding scheme is proposed, and simulation results verify its considerable spectral and energy efficiency advantages compared to traditional mMIMO systems. Finally, we further discuss the challenges, insights, and prospects of deploying reconfigurable mMIMO, along with the associated hardware, algorithms, and fundamental theory.

Reconfigurability enhancement of pixel array antennas based on WOA and MPUC

Reconfigurable pixel antennas are crucial for advancing wireless communication. However, the increasing number of switches results in exponentially growing complexity in antenna configurations. While the complexity holds promise for performance improvements, it also introduces challenges in physical implementation and requires extensive numerical calculations. Thus, an effective design methodology is essential to address these issues. This paper introduces a novel pixel antenna strategy that utilizes the whale optimization algorithm (WOA) and the minimum percentage of useful configurations (MPUC). As a pioneering concept, MPUC explores the impacts of switches on antenna reconfigurability and evaluates their contributions across different topologies. Dynamically assessing switches, the MPUC determines their statuses cyclically. Ultimately, the most reconfigurable antenna is achieved by optimizing switch configurations while enhancing overall reconfigurability. Leveraging WOA, the final antenna configuration is optimized and derived to meet design specifications. Additionally, a comparison is made between antenna configurations derived from traditional optimization methods and the final antenna configuration. Results reveal the superiority of the proposed method, demonstrating a threefold enhancement in design efficiency and reduced switch configurations to achieve comparable electrical performance. These findings validate the efficacy of the WOA and MPUC based strategy in effectively designing larger-scale pixel antennas.

Design of Polarization Reconfigurable Pixel Antennas with Optimized PIN-Diode Implementation

Design of Polarization Reconfigurable Pixel Antennas with Optimized PIN-Diode Implementation

Design of a Wideband, High Steering Angle and Low Side-Lobes Levels Matrix Antenna

This paper presents the use of pixel-type radiating elements in the context of broadband beam steering. The elements are composed of a resonant cavity topped by a frequency selective surface, fed via a patch antenna and filled with dielectric substrates. This pixel antenna has a wide -10 dB matching band from 1.22 to 1.61 GHz, which corresponds to a 27% fractional bandwidth. It has an angular aperture greater than 124° and a realized gain between 3.3 and 3.8 dBi over the whole matching band. An array composed of 5 elements has been simulated and allows a steering on a range of ±60° in the E plane while keeping the gain variation below 3 dB. A prototype has been manufactured and presents a steering capacity between -56 and 53° on the whole band with side-lobes levels lower than -8.1 dB whatever the angle.

Pixel Antenna Optimization Using the Adjoint Method and the Method of Moving Asymptote

The pixel concept offers a convenient and efficient method for antenna design. To meet the given specified antenna requirements or constraints, heuristic algorithms are often used to optimize the connection states for the hardwires between pixels, which are usually assumed to have the binary states, “short” or “open”. An alternative optimization strategy is proposed in this work, where the Boolean constraints on the hardwires are first relaxed to continuously tunable resistances and the globally convergent method of moving asymptotes (GCMMA) is applied to optimize the resistances. To speed up the computation, the adjoint method is used to simplify the calculation of the gradient information required in GCMMA. Resistances that are found as being above or below a certain threshold are then judged as “open” or “short”, respectively. Finally, the remaining intermediate resistance states are binarized using the successive exhaustive Boolean optimization (SEBO) method. Four different optimization strategies are proposed in terms of the objective function implemented in GCMMA and whether the second-stage SEBO is iterative or not. Two broadband endfire pixel antennas having horizontal linear polarization and high radiation efficiency are designed and fabricated correspondingly to demonstrate the feasibility of our proposed methods.

Multiport Pixel Antenna Optimization Using Characteristic Mode Analysis and Sequential Feeding Port Search

An optimization approach for multiport pixel antenna design using <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> -port characteristic mode analysis (CMA) and sequential feeding port selection is proposed. CMA is utilized to characterize the maximum number of independent or orthogonal resonant modes that can be formed in the limited space constrained by the size of the pixel antenna. Once the maximum number of orthogonal resonance modes is found sequential feeding port selection is proposed to find the optimum feed positions to independently excite each of the orthogonal resonance modes. The resulting design does not need additional complex feeding networks or impedance matching circuits, making the physical implementation of the design straightforward, compact and practical. Two examples are provided to verify the performance of the proposed approach, including a 3-port pixel antenna and a 4-port pixel antenna operating at 2.4 GHz. The performance of the optimized antennas is very good, and verifies the usefulness of the proposed approach.

Compact Pattern Reconfigurable Pixel Antenna With Diagonal Pixel Connections

An improved method to design compact pattern reconfigurable pixel antennas is described. The method introduces a new structure consisting of diagonal connections between pixels to enhance the pattern steering capability of the pixel antennas. These diagonal connections increase the number of independent degrees of freedom available in the design process which results in significantly improved performance when compared to designs with only horizontal and vertical connections between pixels. Furthermore, the diagonal structures enable the possible formation of new “cross-over” connections which provide a structure that allows currents to cross each other in the antenna geometry. Simulation and measurement results show that an antenna with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> 6 pixels can steer a beam over 150° in the azimuth plane and 300° beam steering range can be achieved with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times $ </tex-math></inline-formula> 6 pixels. The use of the diagonal elements increases gains by up to 3 dB and provides a much greater steering range when compared to pixel antenna design without the diagonal connections. Utilizing these diagonal pixel connections can also potentially enhance the performance of pixel antenna designs in a wide variety of other pixel antenna configurations.

A Self-Adapting, Pixelized Planar Antenna Design for Infrared Frequencies

Infrared antennas with reconfigurable characteristics offer several advantages in the medical, military, telecommunication and energy harvesting areas, while their design and implementation is a particularly challenging task for the researchers. This paper proposes a pixel antenna, designed for mid-infrared frequencies with a bandwidth more than 25 THz, consisting of 3 × 3 square metallic planar patches. Bolometer-based switches are placed between the adjacent pixels in order to obtain the adaptable characteristics, optimized for the incoming infrared radiation. The incident wave from a certain direction will heat up the bolometers. Consequently, the conductivity of these bolometers (PTC) will be decreased, and as a result they can be considered to turn to OFF state. The simulation results suggest that the proposed structure can steer the antenna pattern toward the direction of the incident radiation in an adaptable manner, thereby considerably increasing the antenna gain. The gain of the antenna can be increased up to 2 dB with respect to the reference one, which makes it a promising structure for various applications.

Pixel Antenna Optimization Based on Perturbation Sensitivity Analysis

Pixel antennas provide a straightforward method for antenna design that can meet a given set of specifications. A key step in the design of pixel antennas is the optimization of the hardwire connections between the pixels in the antenna. Due to the very large number of possible pixel connection combinations, this optimization needs to be performed by heuristic algorithms. In this work, the sensitivity analysis is proposed for the efficient optimization of pixel antennas. In the approach, each individual pixel of the antenna is perturbed in turn to obtain the sensitivity vector of the objective function. The sensitivity analysis at each step is performed efficiently through the use of algebraic simplification that avoids matrix inversion and leads to a significant saving in computational load. The optimization process then selects the perturbation with the greatest sensitivity. Two examples are provided to demonstrate the performance of the proposed optimization method. For both examples, the proposed approach performs the optimization with significantly fewer iterations and either achieves a better or similar minimum in the objective function compared to genetic algorithm approaches. Combined with the efficient computation of the sensitivity vector, significant savings in the computational load are achieved compared to existing approaches.

Pixel Antenna Optimization Using $N$ -Port Characteristic Mode Analysis

A method for using N-port characteristic mode analysis (N-port CMA) for the design and optimization of pixel antennas is described. The motivation for using N-port CMA is to determine the fundamental resonance characteristics of the pixel antenna geometry and optimize them directly. An advantage of this approach is that it separates the process of antenna resonance optimization from impedance matching. It contrasts directly with conventional optimization approaches based on return loss which implicitly perform impedance matching together with antenna resonance optimization. In our work, an objective function based on modal significance is utilized and genetic optimization is used to optimize the desired characteristics. An efficient method for the implementation of N-port CMA is described which requires only one full-wave simulation of the pixel geometry in the optimization process. Impedance matching is performed as a final step in the design process after optimization of the antenna resonance is completed. Simulation and experimental results are provided to demonstrate the utility of the approach. Examples include a triband antenna design for GSM900 (880-960 MHz), DCS1800 (1710-1900 MHz), and IMT-E2600 (2500-2690 MHz), and a dual-band antenna design for GSM900 (890-960 MHz) and DCS + PCS + UMTS bands (1710-2170 MHz).

A Novel Linear Sparse Array with Reconfigurable Pixel Antenna Elements

In this paper, on the basis of multifunctional reconfigurable pixel antenna (RPA) elements, a novel linear sparse array with an attractive compound reconfigurability is presented. It has the potential advantages of its beam scanning with low gain fluctuation, low sidelobe in two orthogonal planes, and polarization reconfigurable performance. Specifically, an RPA with simultaneous polarization and pattern reconstruction capabilities, consisting of the driven patch and the parasitic pixels on the same layer of dielectric substrate, is firstly designed, which can work in several operation modes corresponding to steerable beam directions θ=0°;θxoz=25°, 45°;θyoz=15° with two circular polarizations in X-band. Cross-slot coupling feed is used to improve polarization reconstruction capability and reduce the complexity of hybrid reconstruction topology optimization. Then, those RPAs are integrated into the 1×8 linear sparse array to realize the reconfiguration of two circular polarizations and beam steering in xoz- and yoz-plane. Simulation results show that the gain fluctuation and sidelobe level of the array during beam scanning have significant advantages over the previous phased array, and the generation of antenna grating lobes is avoided. Moreover, both RPA element and RPA array prototypes have been fabricated and measured to testify the efficiency. The measured results agree well with the simulated ones, which indicates the application potential in the field of modern wireless communication system of the proposed linear sparse array.

Small-Size Wide-Band Low-Profile “Pixel Antenna”: Comparison of Theoretical and Experimental Results in L Band

This paper presents a small (≈λ/2 × λ/2) low-profile (λ/10) planar antenna built to work on a very large frequency band (≥40%) for applications in Telecom, Radar, IoT, etc. This antenna is called a “Pixel Antenna” because it was first used as a pixel in an agile beam radiating surface. In this paper, the pixel antenna is used alone to design multiband or wide-band antennas keeping the same radiation pattern and polarization throughout the band. The working principle used to design the Pixel Antenna is deduced from the well-known EBG (electromagnetic band gap) antenna in its low-profile version which already has a bandwidth close to ≈20%. The aim of this present work is to double this bandwidth by simultaneously feeding two modes of the original EBG material. The theoretical and experimental results are compared for an L band application, exhibiting bandwidth from 1 GHz to 1.52 GHz (41%). In addition, good radiation patterns of pixel antenna stay constant over the entire useful band without any degradation of the antenna performance. This proposed antenna design can be used to obtain wide bandwidth for any chosen frequency band (S band, X band, C band, etc.) using frequency scaling.

Fault tolerance of reconfigurable pixel antenna using graph models

This paper discusses the use of graph models for fault tolerance of reconfigurable antennas. Reconfigurable antennas can adapt to their environment and change their operation depending on the user’s request. Graph models are introduced for each configuration of the reconfigurable antenna to achieve the desired radiation performance. The use of graph models reduces the complexity while preserving its reliability allowing incorporations into applications like cognitive radio, MIMO, satellite communication and personal communication. A swifter response time is achieved with less cost and less losses. This method facilitates the development of the programming process for reconfigurable antennas. The graph theory facilitates the software control and also optimizes their performances. Graph modeling is also used to reduce the redundancy, complexity and increases the reliability of the reconfigurable antenna. The full analysis of these parameters allows a better implementation of the reconfigurable antenna in wireless and space communication. These models help the designers to analyze the antenna structures and transforms from bulky devices into mathematical and software models.

A low profile reconfigurable antenna for defense aircrafts

In this paper a low profile frequency reconfigurable antenna is proposed that can conform to the host surface. The proposed design is a pixelated antenna structure with a grid of small metallic patches with RF switches for re-configurability. The prototype of the proposed design is designed on an FR4 substrate with the relative dielectric constant of 4.4 and thickness of 1.6 mm. This antenna is capable of resonating in three different frequencies. The prototype resonates at 10 GHz with return loss of − 12.47 dB and gain of 4.35 dB, 3.9 GHz with return loss of − 19.95 dB and gain of 3.52 dB and 2.6 GHz with a return loss of − 14.22 dB and gain of 4.26 dB. The simulated result shows that the gain of the pixel antenna on FR4 substrate ~ 4 dB comparable to gain attained by pixel antenna on substrates with low tangent loss and low dielectric constant. It is observed that the measured results are in good agreement with the simulated result.

Design and Optimization of Multiport Pixel Antennas

We describe a method for the design and optimization of multiport pixel antennas for application in multiple-input multiple-output (MIMO) communication systems. A rectangular grid of pixels with connections between them is used as a design surface for multiport antenna design. Genetic algorithm optimization is used to find the optimal configuration of connections between pixels and multiple input port locations under the constraints of high isolation between all ports and good impedance matching for all ports over the desired frequency band and/or beam direction. The method utilizes a scalar single-objective function that takes account of return loss, isolation between ports, and antenna gain, and makes use of the internal multiport method. Examples of MIMO antenna optimization for a 2-port MIMO dual-band antenna operating at 2.4 and 5 GHz without pattern optimization and an example for a 2-port MIMO single-band antenna operating at 5 GHz with pattern optimization (forming orthogonal endfire main beams) are provided.

Multiport Pixel Rectenna for Ambient RF Energy Harvesting

We describe the design of a multiport pixel rectenna for ambient radio-frequency (RF) energy harvesting consisting of an optimized triple-port pixel antenna and a triple-port rectifier with dc combining. The advantages of the multiport pixel approach include enhanced harvested RF power for a given area as well as a reduction in the antenna matching requirements. We formulate the design of the triple-port pixel antenna as a binary optimization problem with an objective function related to harvested RF power in the GSM-1800 band for specified power angular spectrums without the need for antenna matching components. The optimization of the triple-port pixel antenna is obtained by using successive exhaustive Boolean optimization. The design for the triple-port rectifier with dc combining is also provided and a prototype is demonstrated. The rectenna measurement demonstrates that the proposed triple-port pixel antenna has dc output power over double that of single-port-based antennas of similar size. The overall RF-to-dc efficiency of the multiport pixel rectenna is also evaluated and shown to be 19% when the total input RF power is −20 dBm. The effects of nonuniformity in the input RF power across antenna ports are also investigated.

Efficient gradient‐based optimisation of pixel antenna with large‐scale connections

An efficient gradient-based optimisation method is proposed for designing pixel antennas with hundreds of connections, where the connections between adjacent square pixel patches are modelled by lossy materials with continuous density variables. The gradients of antenna objective functions with respect to these density variables are derived by the adjoint variable method, at the cost of less than two times of simulation. With a gradient-based optimisation solver, four antennas with 220 connections are optimised. The optimised antennas achieve different expected polarisation and/or radiation patterns. All the optimisations in this work converge in only 80 iterations which is considerably faster than the heuristic algorithms handling the same number of variables. Two of the optimised antennas are fabricated to validate the optimisations. The simulated and measured results verify the accuracy and effectiveness of this method.

Printed Endfire Beam-Steerable Pixel Antenna

A novel design for an endfire beam-steerable planar printed pixel antenna is described. A key performance highlight of the antenna is its ability to beam steer through 300° in the azimuth plane without using any phase shifters. The design consists of a printed half-wavelength driven element and balun with a rectangular grid of parasitic pixels, switches, lumped elements, and dc bias lines on the same layer as the driven element. The pixels can be connected/disconnected together by means of switches, resulting in reconfigurability of the endfire beam direction. Simulation and experimental results are provided for a design operating at 2.5 GHz when p-i-n diode-based switches are used and its bandwidth is approximately 200 MHz (8%). The measured gain for different configurations at 2.5 GHz is 7.5 ± 2 dBi when the endfire beam is steered through a steerable range of over 300° in the azimuth plane. In addition, the effects of the switches on efficiency are also provided. Due to the potential performance of the proposed antenna, it can be considered as a possible candidate for biomedical applications, wearable systems, wireless powered communications, and future wireless communication applications.