High-directivity Antenna Research Articles

High-permittivity ceramics enabled highly homogeneous zero-index metamaterials for high-directivity antennas and beyond

Zero-index metamaterials (ZIMs) can support uniform electromagnetic field distributions at any frequency, but their applications are hampered by the ZIM’s homogenization level—only 3 unit cells per free-space wavelength, which is fundamentally limited by the low-permittivity inclusions (εr ≈ 12) and background matrix (εr ≈ 1). Here, by filling high-permittivity SrTiO3 ceramic (εr ≈ 294) pillars in BaTiO3 (εr ≈ 25) background matrix, we demonstrate a highly homogeneous microwave ZIM with an over threefold increase in the homogenization level. Leveraging such a ZIM, we achieve not only an antenna, approaching the fundamental limit in the directivity with outstanding scalability, but also a concave lens with a focal length of as short as 1λ0. Our highly homogeneous ZIM has profound implications in ceramics, ZIM-based waveguides and cavities, free-space wavefront manipulation, and microwave quantum optics, and opens up enormous possibilities in wireless communications, remote sensing, global positioning satellites, etc.

Research and design of metasurface antennas based on composite dielectric materials

The metasurface has the ability to regulate electromagnetic waves, which is widely used for polarization state control, impedance bandwidth expansion, vortex beam generation, and high-directional antennas. Research shows that the substrate of the metasurface has a significant impact on the performance of the antenna. The equivalent dielectric constant of composite dielectric materials is investigated by using the characteristic mode analysis (CMA). A novel metasurface with composite dielectric substrate is proposed. The composite dielectric material consists of a substrate with a dielectric constant of 3.55 and an air gap. The calculation results of the effective dielectric constant of composite dielectric materials are basically consistent with the simulation results. Based on this composite dielectric material, a metasurface antenna is designed. S11 is less than-10 dB in the frequency range of 5.22–7.87 GHz. The peak boresight gain is 10.44 dBi at 6.5 GHz.

Design and Validation of Water Based Dense Dielectric Patch Antenna (DDPA) for Microwave Communication around Frequency of 1GHz

Liquid antennas are distinct types of antennas that have been widely used due to their low profile, reconfigurable, and tunable features with steering abilities. In this paper, a low profile, high directivity, and good efficiency reconfigurable Water-Dense Dielectric Patch Antenna (DDPA) fed by the coaxial probe is presented. Distilled water becomes lossy above 1 GHZ frequency, so it is best suitable for lower-frequency applications. A thick substrate between the water patch and the ground plane is used. An impedance bandwidth of 7% with a maximum gain of 7.78 dBi, and radiation efficiency up to 71 % is obtained. This antenna can operate over the 967 to 1038 MHz band without a reduction in radiation efficiency. Simulated results are presented to validate the new design in both CST microwave studio and ANSYS HFSS which are the best simulating software for antenna designing. The comparison shows that the new antenna has a more compact size, and simpler structure, and is suitable for low-frequency applications.

Fast prediction of a high directivity antenna characterization for future wireless communication based on terahertz photonics

Fast prediction of high-directivity antenna characterization has been presented. The Cassegrain antenna working at J band frequency has been evaluated using a terahertz (THz) photonic system based on near-field measurement. The generation and detection of THz signal are based on a non-polarimetric electrooptic (EO) frequency down-conversion technique combined with a self-heterodyne system. The synthesis method is introduced to estimate far-field E and H-plane antenna characteristics. The antenna result is calculated using amplitude and phase-synthesized data based on the measured data. A near-field (NF) to far-field (FF) transformation is employed in the antenna radiation pattern. The effect of blocking objects on the antenna (supporting rods and sub-reflector) is discussed. The antenna characteristics of the measured and synthesized data are compared to the ITU F.699 recommendation. The synthesized result agrees with the measured one on the main lobe angle.

A Study on Microstrip Array Antenna with FSS for Next Generation Cellular Communication

Abstract: Fifth-generation wireless, often known as 5G, is the next version of cellular technology and is intended to provide major improvements to the speed and responsiveness of wireless networks. In addition, the increased bandwidth and improved antenna technologies that come with 5G make it possible for a significant increase in the quantity of data that can be transmitted via a wireless network. In order to build a successful next-generation cellular communication system in the terahertz (THz) regime, it is necessary to create high-directivity antennas, which will enable the signal to travel further than 0.1 km. This will allow the system to function effectively. Concurrently, large bandwidth antennas should be designed in order to facilitate the information's transmission

A Reconfigurable Phase-Time Array Transmitter Achieving Keyless Secured Transmission and Multi-Receiver Localization for Low-Latency Joint Communication and Sensing

The vast available spectrum at millimeter-wave (mm-Wave)/terahertz (THz) frequencies is envisioned as a key enabler to solve the ever-increasing data rate needs in crowded urban environments and lead the next wireless technology revolution. To overcome the high path loss present at mm-Wave/THz, highly directional antenna arrays have become ubiquitous. Their future large-scale deployment will naturally create dense wireless sensor networks, which in-turn enable joint communication and sensing. However, the beamforming of high-directivity antenna arrays relies on real-time precise localization between transmitters (TXs) and receivers (RXs) to ensure robustness in dynamic mobile applications. Moreover, traditional digital encryption and decryption at multi-Gbps data rate cause large power and latency overhead, and thus, wireless physical layer security has become a promising solution. In this article, we propose and demonstrate a reconfigurable phase-time array (PTA) TX with prism-like spectral-to-spatial mapping of wideband transmitted signals, which achieves keyless physically secured wireless communication and fast multi-RX localization to enable low-latency joint communication and sensing within the same wireless electronics frontend. The PTA realizes reconfigurable spectral-to-spatial mapping by applying both a phase shift and true time delay (TTD) at each array element. This intentionally creates and exploits the array beam squinting effect, such that different frequency components of a wideband signal are transmitted in different directions, analogous to an optical prism. Therefore, multiple RX nodes can simultaneously determine their angular positions relative to the TX array using their received signals for fast multi-RX localization. Judiciously engineering the prism-like beam squinting in PTA TX can also selectively distort signal transmission to unwanted directions for secured communication without cryptography. Furthermore, the PTA scheme can reconfigure its element-level phase-time delay combinations to attain variable levels of communication security and localization/sensing performance depending on the needs.

Automatic design of pixelated near-zero refractive index metamaterials based on elite-preserving genetic algorithm optimization

Near-zero refractive index metamaterials (NZIM) have drawn a lot of attention recently for the development of high directivity antennas. However, their application has been constrained by the tedious and time-consuming manual design process. In this work, we offer an automated optimization design technique for NZIM that combines a modeling process based on pixelated metamaterials with an optimization process based on heuristic algorithms. The interactive CST-Python simulation is utilized for accomplishing the above automated design. In detail, the elite-preserving genetic algorithm (EGA) is specifically employed because of its improved capacity in locating the superior unit, and the fitness function proposed guarantees the performance of bandwidth and optimization process based on the principles of proportionate integration and penalty-like functions, respectively. Utilizing the suggested technique, we designed a NZIM unit that operates between 8.0 and 8.52 GHz. In order to validate the performance of the NZIM, a rectangular microstrip patch antenna (MPA) resonating at 8.2 GHz was employed as the radiation source for studies. According to the simulation results, the developed NZIM has a clearly beam focusing effect which causes the MPA's spherical waves to converge into quasi-plane waves. Furthermore, discussing the NZIM’s application in high directivity antennas designing, the prototypes of the NZIM and MPA were fabricated and tested. The results revealed that the MPA’s gain enhancement achieves 5.3 dB on average and 6.05 dB on maximum. Due to the automated optimization and design, this work is promised to advance NZIM's further applicability in high directivity antennas.

Analysis of fluctuations of antenna pattern in U-V2X communications

The third-generation partnership project (3GPP) defined several scenarios of vehicle-to-everything (V2X) networks such as vehicle-to-vehicle, vehicle-to-pedestrian, and vehicle-to-infrastructure. Unmanned aerial vehicles (UAVs) exploiting such scenarios for vehicular applications like vehicular-platooning, autonomous driving, and traffic management have shown improved networks’ performance in UAV-V2X (U-V2X) communications. This promising performance is typically obtained by considering high directional UAV antennas. However, the UAV vibration makes UAV antennas’ beam-width sensitive to UAV fluctuations which results in degrading the networks’ performance. Thus, in this paper, the performance of a U-V2X network in the presence of UAV fluctuations is investigated. The UAVs are modeled using an independent homogeneous Poisson Point Process and the vehicular-nodes are modeled using an independent Poisson Line Process. To this end, the association probability and success probability of various links such as vehicular-node connected to a UAV link, vehicular-node connected to a near-by vehicular-node link, and the overall U-V2X link are derived. In addition, the effect of different network settings such as the number of vehicular-nodes, UAVs, roads, and antennas is quantified. Moreover, the spectral efficiency of a U-V2X network is evaluated. Extensive simulations revealed that V2X networks facilitate UAVs and that for less dense areas with fewer roads, buildings, and crowds; UAVs provide more reliable links for connectivity than vehicular-nodes. Furthermore, it is also revealed that UAVs provide less reliable connection for V2X networks with larger UAV antenna fluctuations.

Meta-surface (frequency selective surface) loaded high gain directional antenna systems for ultra-wideband applications

<span lang="EN-US">In this work, a meta-surface (frequency selective surface) loaded high gain directional antenna system is presented. The antenna system is developed using ultra-wideband (UWB) antenna element and meta-surface reflector. The UWB antenna element is designed and simulated without meta-surface reflector. The UWB antenna element has poor impedance bandwidth and directivity. A meta-surface is created using unit cell and equal in the size of the antenna substrate. The meta-surface is placed over the UWB antenna element at optimized height (H=30 mm). The impedance bandwidth, directivity and gain of the proposed antenna are improved by the meta-surface reflector. The proposed antenna is fabricated and experimentally validated by the comparison of the simulated and measured results. The antenna has 3 to 6 GHz wide impedance bandwidth, more than 5 dBi gain and maximum 4.6 dBi directivity at 3.5 GHz frequency. Performance of the proposed antenna is also compared with existing carried out work. Comparatively, the proposed antenna with high directivity is most suitable for IEEE 802.15.4a UWB wireless sensor network (WSN) security application.</span>

Omni-Directional Pathloss Measurement Based on Virtual Antenna Array With Directional Antennas

Omni-directional pathloss, which refers to the pathloss when omni-directional antennas are used at the link ends, are essential for system design and evaluation. In the millimeter-wave (mm-Wave) and beyond bands, high gain directional antennas are widely used for channel measurements due to the significant signal attenuation. Conventional methods for omni-directional pathloss estimation are based on directional scanning sounding (DSS) system, i.e., a single directional antenna placed at the center of a rotator capturing signals from different rotation angles. The omni-directional pathloss is obtained by either summing up all the powers above the noise level or just summing up the powers of detected propagation paths. However, both methods are problematic with relatively wide main beams and high side-lobes provided by the directional antennas. In this correspondence, directional antenna based virtual antenna array (VAA) system is implemented for omni-directional pathloss estimation. The VAA scheme uses the same measurement system as the DSS, yet it offers high angular resolution (i.e. narrow main beam) and low side-lobes, which is essential for achieving accurate multipath detection in the power angle delay profiles (PADPs) and thereby obtaining accurate omni-directional pathloss. A measurement campaign was designed and conducted in an indoor corridor at 28-30 GHz to verify the effectiveness of the proposed method.

Picosatellite identification and Doppler estimation using passive radar techniques

In this article a novel method for satellite identification is presented for picosatellites. Utilizing apriori knowledge of the transmitted signals the cross-correlation of the received signal and a known transmission is calculated, from the results the Doppler shift is estimated and the satellite’s Doppler curve can be matched against the measurements of NORAD. Using this method an omnidirectional antenna can be used instead of a high gain directional antenna, and the gain difference is compensated by the processing gain of the algorithm described. The practicality of the algorithm is demonstrated through the mission of MRC-100 PocketQube.

High-directive multiband microstrip patch antenna for biomedical applications, inspired by metamaterial

Recent advancements in medical technology impose a limited number of devices for biomedical applications. A variety of techniques are being proposed to improve the performance of novel antenna designs in response to the rapid development of modern wireless technologies. A miniaturised microstrip antenna structure based on metamaterial (MTM) is presented here. The objective of this work is to present a high-directive antenna for wireless systems utilising MTM properties. Directivity is improved by the incorporation of the MTM structure on the ground structure. In order to improve the performance parameters of the antenna for medical applications, this study provides the design and analysis of a multiband patch antenna employing split-ring MTM. The split-ring resonator (SRR) MTM structures are embedded in a unique and novel way in the ground structure of the antenna. So that subwavelength modes get introduced in the patch cavity and a good performance characteristics is obtained. The reference antenna is a rectangular microstrip patch antenna exhibiting a directivity of 1.1823[Formula: see text]dB that resonates at a frequency of 2.32[Formula: see text]GHz. The optimised SRR MTM is positioned in the ground plane of the suggested antenna to increase the directivity of the antenna. This technology covers the frequency range between 2.24 and 3.96[Formula: see text]GHz used for biomedical applications and the ultra-wideband (UWB) range from 4.48 to 9.08[Formula: see text]GHz used for medical applications, industrial and scientific areas. The number of gaps of the rectangular-shaped SRRs is a key component of the enhancement of directivity from 1.1823 to 8.88823[Formula: see text]dB.

Design and Implementation of Ku-Band High Directionality Antenna

In this article, a Ku-band high directivity antenna is designed, which consists of a radiation waveguide section, a mode conversion section, and a coaxial waveguide conversion section. In this article, the theoretical calculation process of antenna components is summarized and supplemented. The calculation method between key technical indexes and structural parameters is established. The key technical parameters of the antenna, including input return loss, half-power beamwidth, gain, and cross-polarization level, are studied and explored. The radiation performance of the antenna can be further improved by optimizing the structural parameters. Finite-element analysis and COMSOL simulation software are used to study. In order to reduce antenna reflection, a method of equal-Q impedance transformation is proposed for rectangular and circular waveguide converters and coaxial waveguide converters. Finally, the proposed feed antenna is processed and verified, and the measured results are in good agreement with the simulation results.

Pointing Error Modeling of mmWave to THz High-Directional Antenna Arrays

This paper focuses on providing an analytical framework for the quantification and evaluation of the pointing error at high-frequency millimeter wave (mmWave) and terahertz (THz) communication links. For this aim, we first characterize the channel of a point-to-point communication link between to unstable transmitter (Tx) and receiver (Rx) and then, we derive the probability density function (PDF) and cumulative distribution functions (CDF) of the pointing error in the presence of an unstable Tx and Rx as a function of the antennas' pattern. Specifically, for the standard array antenna, a closed-form expression is provided for PDF of the pointing error, which is a function of the number of antenna elements. Moreover, a more tractable approximate model is provided for the CDF and PDF of pointing error. In addition, using $\alpha-\mu$ distribution, which is a common model for small-scale fading of THz links, the end-to-end PDF of the considered channel is derived and used to calculate the outage probability of the considered system. Finally, by employing Monte-Carlo simulations, the accuracy of the analytical expressions is verified and the performance of the system is studied.

A Novel Approach of a Low-Cost UWB Microwave Imaging System with High Resolution Based on SAR and a New Fast Reconstruction Algorithm for Early-Stage Breast Cancer Detection.

In this article, a new efficient and robust approach—the high-resolution microwave imaging system—for early breast cancer diagnosis is presented. The core concept of the proposed approach is to employ a combination of a newly proposed delay-and-sum (DAS) algorithm and the specific absorption rate (SAR) parameter to provide high image quality of breast tumors, along with fast image processing. The new algorithm enhances the tumor response by altering the parameter referring to the distance between the antenna and the tumor in the conventional DAS matrices. This adjustment entails a much clearer reconstructed image with short processing time. To achieve these aims, a high directional Vivaldi antenna is applied around a simulated hemispherical breast model with an embedded tumor. The detection of the tumor is carried out by calculating the maximum value of SAR inside the breast model. Consequently, the antenna position is relocated near the tumor region and is moved to nine positions in a trajectory path, leading to a shorter propagation distance in the image-creation process. At each position, the breast model is illuminated with short pulses of low power waves, and the back-scattered signals are recorded to produce a two-dimensional image of the scanned breast. Several simulations of testing scenarios for reconstruction imaging are investigated. These simulations involve different tumor sizes and materials. The influence of the number of antennas on the reconstructed images is also examined. Compared with the results from the conventional DAS, the proposed technique significantly improves the quality of the reconstructed images, and it detects and localizes the cancer inside the breast with high quality in a fast computing time, employing fewer antennas.

Analysis of slotted matching antenna for millimeter wave applications

Millimeter wave applications gives an efficient solution to furnish peak data rates in indoor wireless access systems. Propagation of the signal will get up-shot because of few considerations in advanced communication appliances. Superior output and high directivity antennas are mandatory to overcome these consequences. By installing unequal slots in the structure, the tree-shaped unequal slotted antenna is analyzed for the variations in impedance, directivity changes and reflection coefficient. The better quality results have been observed for the proposed structure while compare with existing structures. The maximum simulation reflection coefficient(S11) of tree-shaped unequal slotted antenna is 45.12 dB, directivity is 6.54 dBi with the efficiency of 60 % and at 60 GHz, and the measurement value of 36.35 is observed which covers the complete RADAR applications which have an unlicensed bandwidth. The dimension of tree-shaped unequal slotted antenna is observed as 12*7*0.508 mm3. The proposed tree-shaped unequal slotted antenna is well suited for millimeter-wave appliances such as Microcell, Femtocell and macrocell applications because of its good bandwidth and less dimension.

Mitigating Interference and Blockage Through Fingerprinting in Mmwave-Enabled HetNets

One of the most critical challenges of future generation cellular networks is to meet the unprecedented cellular traffic demands from mobile applications. mmWave has large chunks of spectrum and is a promising candidate to satisfy the ever-increasing traffic demand. Unfortunately, the characteristic that mmWaves have high attenuation against physical objects and even atmosphere hinder its feasibility. High gain directional antennas are required to combat the attenuation. However, user mobility might change the signal direction, introducing physical objects in the line-of-sight of the signal. Additionally, user mobility might also make two directional signals interfere with each other. The blockage and interference incidents must be handled with care. In this paper, we propose to predict blockage and interference incidents so that countermeasures can be applied in advance. We let the cells collect the fingerprints, which are transmission parameters when blockage and interference incidents happen. The cells attempt to predict blockage and interference incidents by matching their current transmission parameters with the collected fingerprints. When a user is moving, and the cell's transmission parameters are approaching a fingerprint, the HetNet takes necessary actions to mitigate interference or avoid disconnection before it happens. Our results show that for typical indoor scenarios, most of the blockage and interference can be predicted, and taking countermeasures in advance improves overall performance.

Near-zero-index-featured multi-band highly directional radiator with large Purcell factors

Near-zero-index medium could be used to produce perfect planar wave beams, allowing for the design of compact antennas, but implementation is difficult due to the bandwidth and loss limitations. This work proposes a new method for achieving highly directional radiation by introducing a near-zero-index-featured resonator based on optical conformal mapping. The conceptual device performs the same functions as resonators filled with near-zero-index media but can be realized using dielectrics with refractive index n ≥ 1. Multi-band highly directional radiation with large Purcell factor is numerically demonstrated by the proposed high-Q resonator, which may pave the way for efficient production of high gain directive antennas in radar systems.

Multipole-Based Electrically Small Unidirectional Antenna With Exceptionally High Realized Gain

Electrically small, high-directivity antennas are in demand for a variety of current and future wireless applications. An electrically small directive antenna (ESDA) that requires only one specially engineered port to excite a set of multipoles is demonstrated in this article. Four 90° copper sectors are combined with additional structures and fed with a coaxial cable. Two resonant quadrupoles (equivalent to two pairs of resonant electric dipoles) and one magnetic dipole are excited. Both high radiation efficiency and good impedance matching are achieved. Theoretical calculations, numerical simulations, and experimental measurements are shown to be in good agreement. An optimized prototype is designed, fabricated, and tested. The measured results confirm that it is a supergain system. The unidirectional ESDA has a peak directivity of 6.71 dBi, a peak realized gain of 6.31 dBi, radiation efficiency of 94.5%, and a front-to-back ratio of 14.89 dB at its resonance frequency, 814 MHz. Its height is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.06 \lambda _{\mathrm{ res}}$ </tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ka = 0.98$ </tex-math></inline-formula> . These measured realized gain and directivity values exceed both the Harrington and Kildal–Best <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ka$ </tex-math></inline-formula> -based upper limits.

A General Model for Pointing Error of High Frequency Directional Antennas

This paper focuses on providing an analytical framework for the quantification and evaluation of the pointing error for a general case at high-frequency millimeter wave (mmWave) and terahertz (THz) communication links. For this aim, we first derive the probability density function (PDF) and cumulative distribution functions (CDF) of the pointing error between an unstable transmitter (Tx) and receiver (Rx), that have different antenna patterns and for which the vibrations are not similar in the Yaw and Pitch directions. The special case where the Tx and Rx are both equipped with uniform linear array antenna is also investigated. In addition, using α-μ distribution, which is a valid model for small-scale fading of mmWave/THz links, the end-to-end PDF and CDF of the considered channel is derived for all the considered cases. Finally, by employing Monte-Carlo simulations, the accuracy of the analytical expressions is verified and the performance of the system is studied.