Conventional Antenna Array Research Articles

Mutual Coupling Reduction Using Electromagnetic Band Gap Structures

This paper introduces a novel technique to reduce mutual interference in antenna arrays. In a conventional antenna array, radiating elements placed on the same ground plane generate strong surface waves, which propagate through the ground plane and cause interference. When these radiating elements are closely spaced, strong mutual coupling occurs. This study involved designing a 1x2 patch antenna array on a FR-4 substrate with an edge-to-edge spacing of 0.2λ. To mitigate the effects of surface waves, a high-impedance surface was created using Electromagnetic Band Gap (EBG) structures. Incorporating Mushroom EBG (MEBG) unit cells with the antenna elements, mutual coupling was reduced by 2.3 dB, making the design suitable for wireless applications at 5.2 GHz. With the support of HFSS software, the proposed antenna array was designed and simulated.

Active differential reflection coefficient analysis of differentially-fed antenna array

In this paper, a definition for the active differential reflection coefficient of the differentially-fed antenna array is proposed. Each antenna is fed by the differential port with the equal-amplitude anti-phase signal input. According to the active reflection coefficient of the conventional single-ended antenna array, the active differential reflection coefficient definition of the differential antenna array is given and analyzed. It is derived that the active differential reflection coefficient of the differential port m is half of the active reflection coefficient sum for the single-ended port m + and m −. In addition, the active differential impedance expression is also given. To verify the active differential reflection coefficient, a differential three-element microstrip patch antenna array was designed, fabricated, and measured. The experimental results validate the proposed theoretical analysis. This work will provide a new insight into the differential antenna array.

Sidelobes and sideband minimization in time-modulated array antenna based on chaotic exchange nonlinear dandelion optimization algorithm

Time-modulated array antenna (TMAA) is a new type of array antenna based on time modulation technology. By introducing "time" as the fourth dimensional design freedom into the design of conventional array antennas in three-dimensional space, the array antenna has time modulation characteristics, which better controls the radiation characteristics of the array antenna and achieves the best far-field radiation pattern synthesis. This paper designs a Time-modulated linear array (TMLA) with low sidelobe level (SLL) and low sideband level (SBL) based on the chaotic exchange nonlinear dandelion optimization (CENDO) algorithm. Three optimization methods are studied: firstly, determining the optimal on-time (τnn) for each array element; The second is to determine the optimal on-time (τnn) and optimal uniform array element spacing (d) for each array element; The third is to determine the optimal opening time (ton), closing time (toff), and optimal uniform array element spacing (d) for each array element. To achieve simultaneous reduction of sidelobe level and suppression of harmonic interference. The same array model contains different harmonic frequency radiation. In this article, we only considered two harmonic frequencies, namely the first sideband frequency and the second sideband frequency. Because the harmonic of other sideband frequencies has a very small impact on the radiation of the fundamental wave, it can be ignored. To demonstrate the stronger ability of the CENDO algorithm in optimizing Time-modulated array antennas, and in line with the principle of fairness and impartiality, this paper also simulates different Time-modulated array models and compares the results of the CENDO algorithm with other published literature. It is concluded that this study shows lower SLL and lower SBL in different models. This provides a more scientific and accurate explanation of the superiority of the CENDO algorithm compared to other algorithms in the field of antenna optimization in electromagnetics. At the same time, this also provides great research value and fundamental support for designing high-performance Time-modulated array antennas in subsequent engineering applications.

Gain Enhancement and Ground Plane Immunity of Mechanically Driven Thin‐Film Bulk Acoustic Resonator Magnetoelectric Antenna Arrays

AbstractCompact, conformal antennas with ground plane immunity and high gain are crucial to IoT, 5G, and biomedical applications. Conventional electrical antennas suffer large size, detuned impedance, and degraded gain and radiation efficiency on a ground plane as they operate on electromagnetic resonance and use electric dipole for radiation. Utilizing electromechanical resonance, magnetoelectric(ME) coupling, and magnetic dipole radiation in magnetostrictive/piezoelectric heterostructures, ME antennas exhibit ultra‐compact sizes comparable to acoustic wavelength and enhanced radiation performance on a ground plane. This study first utilizes parallel and series antenna array topology to achieve a profound gain and radiation efficiency enhancement without degrading impedance mismatch and quality factor of ME resonators. Notably, by increasing the array element number, 10 dBi gain enhancement is achieved in 3 × 3 thin‐film bulk acoustic resonator (FBAR) ME antenna array, reaching a peak antenna gain of −17.3 dBi. Unlike conventional antenna arrays, ME antenna arrays enhance radiation efficiency without affecting directivity, owing to ultra‐compact dimensions much less than one‐quarter of electromagnetic wavelength. Their ground plane immunity and 3 dB gain enhancement on ground planes with different shapes are also demonstrated. The demonstrated ME antenna arrays are outstanding platform‐independent ultra‐compact high‐gain conformal antenna candidates for wireless communication, wireless power transfer, and portable electronic and biomedical devices.

A Substrate Integrated Waveguide Slotted Antenna

Introduction. Slotted waveguide antenna arrays are widely used across centimeter- and millimeter-wavelength ranges due to numerous advantages, including their good directional properties, compact dimensions, flat shape, convenience of power supply, and high efficiency. At the same time, the current trend toward miniaturization of electronic devices and their integration requires new solutions, such as the development of devices based on wave-guides integrated into the substrate (Substrate Integrated Waveguide – SIW).Aim. To simulate a SIW-based slotted antenna with characteristics similar to those of a conventional antenna array based on a hollow metal waveguide.Materials and methods. The Ansys HFSS software was used to simulate the structure under study and to carry out electro-magnetic modeling and analysis of its directional properties. The energy method was used to determine the coordinates of longitudinal slots on the wide wall of the SIW waveguide. Macros were developed in the Visual Basic Scripting Edition language to automate routine operations for creating and deleting objects of the same type when constructing a model. The Arlon AD300C microwave material was used to manufacture a printed version of the SIW waveguide.Results. The process of developing a SIW slotted antenna was carried out in the following stages: construction of a reference model based on a hollow metal waveguide followed by creating a transition model based on a waveguide completely filled with a dielectric and the final SIW-based model. At each stage, the radiation pattern was monitored to obtain the directional properties of the SIW slotted antenna with characteristics identical to those of an antenna based on the reference hollow metal waveguide.Conclusion. A SIW slotted antenna with the required characteristics was simulated and tested in the Ansys HFSS environment. Such an antenna employs one of the main advantages of the SIW technology, i.e., the possibility of integrating all components on a single substrate, including antenna arrays, passive components, and active elements. This approach provides the basis for reducing the size of microwave devices and their miniaturization.

A high-order TE50 mode waveguide with single mode transmission property and its application in slot array antenna

Conventional array antenna techniques contain various feeding networks, such as T-junction power dividers, phase dividers, and baluns. To feed a relatively large array, one can cascade the traditional T-junction power dividers, resulting in the increase of design complexity. In this paper, an overmoded waveguide supporting the single mode propagation of TE50 mode, is presented. Since TE50 mode can be separated into five TE10 modes with equi-amplitude and opposite phase properties, it is advisable to distribute the input signal flexibly and decrease the cascading of the T-junctions for the traditional feeding networks. To actualize a TE50 mode waveguide, several rows of metallic blocks acting as metamaterial are periodically loaded inside an overmoded waveguide to tailor the dispersion of the waveguide modes and yield the proposed mode bandgaps. Considering the Bloch theory, parts of the undesired waveguide modes are not supported inside the metamaterial and will be removed by these bandgaps. In addition, central feeding method is used to suppress the unwanted modes further in light of mode mismatch. As a proof-of-concept, we drilled the slot array on the top of the overmoded waveguide directly and give rise to a pencil beam radiation along the broadside with 15–17 dBi realized gain among 9.4–10.6 GHz, which demonstrates the stable feeding ability of TE50 mode.

Circularly Polarized Polarization Conversion Metasurface-Inspired Antenna Array With Low RCS Over a Wide Band

A circularly polarized (CP) metasurface-inspired antenna array with low radar cross section (RCS) over a wideband based on polarization conversion metasurface (PCM) is proposed. Without increasing the structural complexity, the PCM units serve directly as antenna radiators, which not only maintains good radiation characteristics but also reduces both the in-band and out-of-band RCS of the antenna. Simulations show that the proposed PCM-inspired antenna array has an impedance bandwidth of 37.6% (8.2 to 12 GHz), a 3 dB axial ratio (AR) bandwidth of 32.5% (8.5 to 11.8 GHz), and a 3 dB gain bandwidth of 23.3% (9.5 to 12 GHz). The RCS of the proposed antenna array is greatly reduced for both polarizations in the frequency range of 7.6 to 16.2 GHz (72.3%) compared to conventional microstrip patch antenna array, with a maximum reduction of 20.6 dB. Moreover, the proposed PCM-inspired antenna array has a smaller element size compared to conventional low-RCS metasurface antennas, making it more conducive to the composition of a phased array. Finally, the proposed array is fabricated and measured, and the results confirm the simulations.

Helicopter-Mounted HF Direction-Finding Antenna With Rotor-Blade Modulation Using the Characteristic Mode Theory

A single helicopter-based high frequency (HF) antenna is proposed for direction finding (DF) using rotor-blade modulation. Without integrating additional antenna structures, a landing gear is utilized as a coupling element to excite a combination of significant characteristic modes of the helicopter through characteristic mode (CM) analysis. Different from traditional DF systems where multiple antennas required, incoming signal receptions are achieved by a single radiator in this work. The diversity in antenna radiation patterns is realized by incorporating main rotor-blade rotations. The incident signals can be measured as the blade rotates from 0° to 75°, where the helicopter-mounted antenna with each rotation angle is equivalent to one antenna element in a conventional DF antenna array. Correlation coefficients of complex CM and excited radiation patterns between the antenna with different blade rotation angles are calculated to demonstrate pattern diversity. Both Cramer-Rao bound (CRB) and multiple signal classification (MUSIC) algorithm are investigated using the complex CM and excited radiation patterns to validate the azimuthal DF capability of the helicopter-integrated single antenna.

Lightning VHF Radiation Mapping Method for an Irregular Short‐Baseline Array

AbstractLightning very high frequency interferometry is a crucial tool for studying the development of lightning leaders within thunderclouds, and the conventional antenna array is composed of two coplanar orthogonal baselines. In this study, we develop two new location methods for an irregular array based on the optimization algorithm, using all baselines in the calculation. Besides, we have analyzed the effects of two kinds of time uncertainty on the location result and provided a calibration method. The first type—the systematic time drift of antennas—can induce an offset on the location result, leading to a worse accuracy. We can calibrate the time drift of each antenna efficiently during the experiment. The second type—the waveform distortion between different antennas—can introduce the noise on time, leading to worse precision. The location precision improves when more baselines are used, whether they are independent or redundant. Our result shows that the non‐coplanar configuration can significantly improve the elevation uncertainty near the horizon and the azimuth uncertainty near the zenith after considering the angular uncertainty's theoretical distribution.

Virtual antenna array for reduced energy per bit transmission at Sub-5 GHz mobile wireless communication systems

This paper presents an innovative technique to synthesize a virtual antenna array (VAA) that consumes less energy than conventional antenna arrays that are used in mobile communications systems. We have shown that for a specific spectral efficiency a wireless system using the proposed virtual antenna array consumes significantly less energy per bit (∼3 dB) than a wireless system using a conventional multiple-input multiple-output (MIMO) array. This means the adoption of the proposed VAA technology in smartphones, iPad, Tablets and even base-stations should significantly reduce the carbon footprint of wireless systems. The proposed VAA is realized by employing a pair of linear antenna arrays that are placed in an orthogonal configuration relative to each other. This orthogonal arrangement ensures the radiation is circularly polarized. The size of the standard radiating elements constituting the VAA were miniaturized using the topology optimization method. The design of the VAA incorporates substrate integrated waveguide (SIW) and metasurface technologies. The function of SIW in the design was twofold, namely, to reduce energy loss in the substrate on which the VAA is implemented, and secondly to mitigate unwanted electromagnetic interactions between the neighboring radiating elements and thereby enhancing isolation which otherwise would degrade the radiation characteristics of the array. Metasurface technology served to effectively increase the effective aperture of the array with no impact on the footprint of the array. The consequence of SIW and metasurface technologies was improvement in the gain and radiation efficiency of the array. The proposed four orthogonal 4-element VAA covers the entire sub-5 GHz frequency range, and it radiates bidirectional in the azimuth plane and omni-directional in the elevation plane. Moreover, it is relatively easy to design and fabricate. The proposed VAA has dimensions of 0.96λ0 × 0.96λ0 × 0.0016λ0 at mid-band frequency of 3 GHz. VAA has a measured gain of 25 dBi and radiates with 90% efficiency. The average isolation between the linear arrays constituting the virtual array is better than 27 dB.

Nonuniform-Array-Based Integrated MIMO Communication and Positioning in Wireless Local Area Networks

The angle of arrival (AoA) is a vital parameter for geometry-based 3-D indoor positioning. Considering a wireless local area network (WLAN) as an example, a conventional antenna array designed for multiple-input–multiple-output (MIMO) communication is not suitable for AoA estimation due to the angle ambiguity introduced by the large interelement spacing (IES). Consequently, the integration of positioning and communication functions using the same radio frequency (RF) frontend and the array would be highly valuable. A nonuniform array (NUA) is proposed to solve this challenging problem. The NUA is optimized to achieve unambiguous angle estimation while maintaining high-capacity WLAN MIMO communication. Moreover, based on the estimated MIMO channel state information (CSI), an improved trilinear parallel factor (TPF) decomposition method is proposed to accurately estimate AoAs with low complexity. Simulated and experimental results show that the proposed NUA-based scheme can achieve decimeter-level 3-D positioning accuracy.

Design and Implementation of a 2.4-GHz Fully Integrated Butler Matrix for Smart Antenna System

This work proposes and analyzes a low-cost fixed microstrip beamforming system based on a uniform linear array with four rectangular patch antennas controlled by a Butler matrix that operates in the 2.4 GHz ISM band. A 4×4 Butler matrix consisting of four hybrid quadrature directional couplers, two crossovers, and two 45° phase shifters was designed and implemented to control the beam direction of the entire system. Similarly, a comparative study is performed between two different antenna arrays, the first consisting of a conventional linear antenna array and the second antenna array consisting of four patch antennas loaded with metamaterial structures on the ground plane. Finally, the electrical performance of both smart beamforming systems was evaluated, and their potential application as a wireless power transmitter was evaluated. Four beams with distinct orientations were created in each situation. The smart antenna based on a conventional array has a higher gain, while the smart antenna based on metamaterial structures has a higher HPBW.

Analysis of Exponential Frequency-Diverse Array for Short-Range Beam-Focusing Technology

The frequency-diverse array (FDA) is a promising technology because of its angle- and range-dependent beam pattern. The FDA has unique properties, such as beam scanning and focusing, which are difficult to achieve using the conventional phased antenna array theory. In this study, the relationship between range and frequency increment is analyzed, and the fundamental operation principle of FDA is thoroughly investigated. The effect of coupling among antenna elements is also discussed to analyze the FDA theory. Furthermore, a novel exponential FDA method for short-range beam focusing is presented based on the proposed FDA analysis method. The proposed method has been investigated through various case studies and applied to research efforts on FDA methods. The FDA design procedures and analysis methods are also presented in this article.

A Low-Scattering Vivaldi Antenna Array With Slits on Nonradiating Edges

To reduce in-band scattering over a large angular range, this communication presents a low-scattering Vivaldi antenna array with cutting slits on the nonradiating edges of each antenna element. Over-concentrated overlap between structural modal and antenna modal scattering currents motivates the novel slit design over the nonradiating edges. These slits separate the structural modal and antenna modal scattering currents in the largest extent. The structural modal scattering is then suppressed through a cavity like structure in the nonradiating portion, while the antenna modal scattering currents keep unchanged as they are crucial for the radiation performance. The design features with a simple structure, while effectively reduces the in-band radar cross Section (RCS) in a wide angular range of ±70° and achieves ±60° scanning in the E-/H-planes over the entire X-band. Prototypes for the proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 Vivaldi antenna array and a reference conventional Vivaldi antenna array are fabricated, assembled, and measured. Both measured and simulated results demonstrate the effectiveness of the low-scattering Vivaldi antenna array design.

Rapid Design of 3D Reflectarray Antennas by Inverse Surrogate Modeling and Regularization

Reflectarrays (RAs) exhibit important advantages over conventional antenna arrays, especially in terms of realizing pencil-beam patterns without the employment of the feeding networks. Unfortunately, microstrip RA implementations feature narrow bandwidths, and are severely affected by losses. A considerably improved performance can be achieved for RAs involving grounded dielectric layers, which are also easy to manufacture using 3D printing technology. Regardless of the implementation details, a practical bottleneck of RA design is the necessity of independent adjustment of a large number of unit cells, which has to be carried out using full-wave electromagnetic (EM) simulation models to ensure reliability. The associated computational costs are extraordinary. A practical workaround is the incorporation of surrogate modeling methods; however, a construction of accurate metamodel requires a large number of training data samples. This letter introduces an alternative RA design approach, where the unit cells are adjusted using an inverse surrogate model established with a small number of anchor points, pre-optimized for the reference reflection phases. To ensure solution uniqueness, the anchor point optimization involves regularization, here, based on the minimum-volume condition for the unit cell. The presented approach reduces the computational cost of RA design to a few dozens of EM analyses of the cell. Several demonstration examples are provided, along with an experimental validation of the selected RA realization.

A Kind of Antenna Array Based on Dielectric Antenna with Small Size

Based on the antenna array design method, a new antenna array is designed in this paper. The optimization design results show that the existence of dielectric materials can effectively compress the electromagnetic field, which could greatly reduce the antenna size. The design results show that the size of this type of antenna array is 126mm * 126mm, which is only 70% of the conventional antenna array, the working frequency is 2.4GHz, the return loss is not more than -10dB, the gain is not less than 12dBi, the half power beam width is not more than 40 degrees and the design results show that the dielectric antenna array has excellent performance and good application prospect in the modern communication system.

Proactive Conformal Waveguide Slot Array Antenna to Synthesize Cosecant Squared Pattern Based on 3-D Printing Manufacturing Process

It is difficult for a standing-wave waveguide slot array antenna to generate a complex beam shape in H-plane, such as the cosecant squared pattern. The reason is that a conventional standing-wave waveguide slot array antenna cannot flexibly and independently adjust the amplitude and phase of radiating elements. In this article, a proactive conformal waveguide slot array antenna is designed with the cosecant squared pattern in its H-plane. It is able to control the element phase by proactively curving the array shape. That means the antenna shape is employed as a new parameter to break the limitation in the phase control. Based on this, the proactive conformal waveguide slot array antenna can modulate the element amplitude and phase independently to form the desired complex far-field pattern. The commercial selective laser melting (SLM) technology is applied to print the curved antenna after carefully considering the printing direction and slot shape. A 35 GHz prototype antenna is fabricated and measured. Good performance can be observed in the measured results.

Antenna Array Performance Diagnostics Using Theory of Collapsed Distributions

The wide bandwidth and wide scan volume are the most desirable features for the antenna arrays meant to be utilized to develop phased array antennas for applications such as radars, 5G wireless networks, Satellite On Move (SatOnMov) vehicular applications, MIMO, etc. The various array parameters as directivity, half power beam width (HPBW), sidelobe level (SLL), average inter-element spacing, etc. are required to characterize these arrays and validate their applicability to the chosen application by the designer. The analysis and synthesis of these arrays are sometimes computationally intensive in case of large arrays with arbitrary shapes due to involved analytical expressions or mathematics which are required to be solved to compute the array parameters. This makes design and optimization a tedious procedure. This article proposes a methodology based on the theory of collapsed distributions (TCD) to reduce the computation time drastically and demonstrate few designs of wide scan antenna arrays. The prediction of the effect of the mutual coupling and the onset of grating lobes is made by introducing the concept of mean or average inter-element spacing computed using TCD. A sparse antenna array having superior scan performance in comparison to the conventional regular or dense antenna arrays is designed and demonstrated using TCD.

Spatial-Spectral Terahertz Networks

This paper focuses on the spatial-spectral terahertz (THz) networks, where transmitters equipped with leaky-wave antennas send information to their receivers at the THz frequency bands. As a directional and nearly planar antenna, the leaky-wave antenna allows for information transmissions with narrow beams and high antenna gains. The conventional large antenna arrays are confronted with challenging issues such as scaling limits and path discovery in the THz frequencies. Therefore, this work exploits the potential of leaky-wave antennas in the dense THz networks, to establish low-complexity THz links. By addressing the propagation angle-frequency coupling effects, the transmission rate is analyzed. The results show that the leaky-wave antenna is efficient for achieving the high-speed transmission rate. The co-channel interference management is unnecessary when the THz transmitters with large subchannel bandwidths are not extremely dense. A simple subchannel allocation solution is proposed, which enhances the transmission rate compared with the same number of subchannels with the equal allocation of the frequency band. After subchannel allocation, a low-complexity power allocation method is proposed to improve the energy efficiency.

A digital SIW-slot antenna array with FPGA implementation of beamforming

The future satellite platform and 5G communication systems place high demands on antennas, in which the antenna should offer low-cost, lightweight, electronically steerable features. In this paper, the design of a digital slot antenna element based on substrate integrated waveguide (SIW) is proposed. SIW guides the microwave inside the substrate confined with planar metallic covers and through-hole synthetized side-walls in conventional applications, and can also radiate the microwave towards free space in antenna applications through opening slots in its metallic covers. The slot antenna element is realized by implementing PIN diodes across the gaps on both sides of the pad in the center of the slot antenna, to provide the switching freedom of the slot antenna element between radiating and non-radiating states. Besides, radial decoupling stubs are introduced into the bias line so as to reduce the leakage of the energy in the SIW structure. Applying a series of on/off states to the diodes produces various radiation patterns, thus wide range scanning is possible supposing that enough array elements are equipped. Finally, a digital SIW-slot array composed of 8 by 4 elements with tunable field programmable gate array circuits are fabricated and measured. The measured results validate the reconfigurable characteristics for the radiation pattern of the proposed digital SIW-slot antenna array without heavy engineering of phase shifter in conventional antenna arrays. The antenna is consisted by 4 by 8 elements and its dimension, simulated gain and radiation efficiency are 145 mm times 127 mm times 1.524 mm, 15 dBi and 53.5%, respectively. Our designed SIW antenna has the advantage of both size and weight. Furthermore, its digitalized control of beamforming allows a programming-friendly interface for smart antenna development.