Search

A low‐profile circularly polarised (CP) metasurface antenna is proposed, utilising characteristic mode analysis (CMA). The antenna design features a two‐layer laminated substrate, a 4×4 Butterfly‐shaped metasurface, a rectangular slot, an irregular transmission line, and a ground plane. The metasurface is analysed using mode significance (MS), characteristic angle (CA), and characteristic current to determine the resonance bandwidth and CA resonance points, which exhibit a near 90° difference. At the intersection of the two MS modes, their CAs differ by nearly 90°, and their far‐field radiation directions align, indicating the potential for achieving circular polarisation at the desired frequency. The integration of the metasurface with the slot antenna is simulated to validate the CMA findings. Additionally, the CP bandwidth is enhanced by modifying the transmission line branches. Measurement of the fabricated antenna reveals an impedance bandwidth (IBW) of 27.4%, a 3‐dB axial ratio bandwidth (ARBW) of 10.1%, and a peak gain of 6.9 dBic at 4.4 GHz. Compared to the design without branches, IBW and ARBW have increased by 10% and 7.3%, respectively. [ABSTRACT FROM AUTHOR]

Abstract The traditional co‐polarised metasurface achieves 360° phase coverage only at the resonant frequency but not full phase coverage across a wide bandwidth. This paper proposes a multilayer structure metasurface, which composes of five layers of metal patch and four layers of medium, forming the Fabry–Perry resonator, using the principle of the cancellation of two polarisation conversion, which can achieve a wideband efficient co‐polarisation transmission. Based on the metasurface transmission phase principle, 360° phase coverage has been achieved by changing the geometric parameters of the intermediate metal patches. Through phase compensation arrangement, a metalens is designed using the proposed metasurface unit cell. At the same time, horn antenna is used as a feed to feed the metalens, which can significantly improve the gain of the antenna within a wideband. Simulated and measured results show that the proposed metalens antenna operates at 22–26 GHz, and the maximum measured gain of the metalens antenna reaches 24.16 dBi at 25 GHz, which is 10.85 dB higher than the horn antenna without metasurface compensation, showing good focusing performance. The proposed multilayer metasurface breaks the narrow band limit of the traditional stacked metasurface in principle, opening a way in the broadband metasurface design.

Abstract A novel synthesis design approach to multimode resonant, azimuthal null frequency scanning antennas (ANFSAs) coordinated by null‐depth is presented. The antenna is composed of a principal radiator and an auxiliary one fed by different ports. A synthesis chart gauged by different null‐depths is developed to determine the respective exciting amplitude and phase conditions for the principal and auxiliary radiators. As is theoretically demonstrated and numerically verified, the ANFSA can exhibit an adjustable null‐depth varying from −12∼−30 dB. A three‐port unequal‐split power divider with the simplest configuration is properly designed, utilised and integrated to meet the oriented power and phase conditions. A prototype with in‐band null‐depth of −30 dB is designed, fabricated and validated in such a way that its available bandwidth can reach up to 32.7%, and the null can continuously scan from φ = 160°–275° in azimuth plane.

The traditional co‐polarised metasurface achieves 360° phase coverage only at the resonant frequency but not full phase coverage across a wide bandwidth. This paper proposes a multilayer structure metasurface, which composes of five layers of metal patch and four layers of medium, forming the Fabry–Perry resonator, using the principle of the cancellation of two polarisation conversion, which can achieve a wideband efficient co‐polarisation transmission. Based on the metasurface transmission phase principle, 360° phase coverage has been achieved by changing the geometric parameters of the intermediate metal patches. Through phase compensation arrangement, a metalens is designed using the proposed metasurface unit cell. At the same time, horn antenna is used as a feed to feed the metalens, which can significantly improve the gain of the antenna within a wideband. Simulated and measured results show that the proposed metalens antenna operates at 22–26 GHz, and the maximum measured gain of the metalens antenna reaches 24.16 dBi at 25 GHz, which is 10.85 dB higher than the horn antenna without metasurface compensation, showing good focusing performance. The proposed multilayer metasurface breaks the narrow band limit of the traditional stacked metasurface in principle, opening a way in the broadband metasurface design. [ABSTRACT FROM AUTHOR]

A novel synthesis design approach to multimode resonant, azimuthal null frequency scanning antennas (ANFSAs) coordinated by null‐depth is presented. The antenna is composed of a principal radiator and an auxiliary one fed by different ports. A synthesis chart gauged by different null‐depths is developed to determine the respective exciting amplitude and phase conditions for the principal and auxiliary radiators. As is theoretically demonstrated and numerically verified, the ANFSA can exhibit an adjustable null‐depth varying from −12∼−30 dB. A three‐port unequal‐split power divider with the simplest configuration is properly designed, utilised and integrated to meet the oriented power and phase conditions. A prototype with in‐band null‐depth of −30 dB is designed, fabricated and validated in such a way that its available bandwidth can reach up to 32.7%, and the null can continuously scan from φ = 160°–275° in azimuth plane. [ABSTRACT FROM AUTHOR]

Abstract The authors extend the resonant modal theory (RMT) developed previously for a metal object to an arbitrary source region consisting of metals, dielectrics, or a combination of both. The influences of dielectrics on the fields are replaced by equivalent volume sources through the use of the compensation theorem in electromagnetic theory. The resonant frequencies can be determined by finding the roots of the determinant of the matrix resulted from the discretisation of the real homogeneous volume–surface integral equation derived from the requirement that the difference of stored field energies in the source region vanishes. As applications of the extended RMT, three examples have been investigated. The first example is a dielectric resonator antenna and is designed by exciting the first resonant mode of the composite structure in which the dielectric cylinder is combined with a conformal metallic strip. The second example is a dual‐band dielectric‐coated metallic wire antenna. The third example studies the resonant modes of a rectangular patch antenna.

This letter proposes a novel planar endfire circularly polarized antenna with widened half‐power beamwidth. Widened azimuth beamwidth mechanism of 2D sectorial electric dipole is theoretically revealed, thus it is able to combine with a rectangular magnetic dipole to yield a half‐power beamwidth widened planar endfire circularly polarized antenna. Finally, a prototype planar endfire circularly polarized antenna with sectorial flared angle of α = 270° is fabricated, simulated, and implemented to validate the design approach. As investigated, the antenna exhibits broadened azimuth half‐power beamwidth of 150° over a frequency range of 2.40–2.45 GHz. [ABSTRACT FROM AUTHOR]

The authors extend the resonant modal theory (RMT) developed previously for a metal object to an arbitrary source region consisting of metals, dielectrics, or a combination of both. The influences of dielectrics on the fields are replaced by equivalent volume sources through the use of the compensation theorem in electromagnetic theory. The resonant frequencies can be determined by finding the roots of the determinant of the matrix resulted from the discretisation of the real homogeneous volume–surface integral equation derived from the requirement that the difference of stored field energies in the source region vanishes. As applications of the extended RMT, three examples have been investigated. The first example is a dielectric resonator antenna and is designed by exciting the first resonant mode of the composite structure in which the dielectric cylinder is combined with a conformal metallic strip. The second example is a dual‐band dielectric‐coated metallic wire antenna. The third example studies the resonant modes of a rectangular patch antenna. [ABSTRACT FROM AUTHOR]

Abstract A planar antenna with dual‐linearly polarised end‐fire radiation is proposed. A tapered double‐sided symmetrical spoof surface plasmon polariton (SSPP) transmission line (TL) with tilted unit cells is proposed. The SSPP TL can operate in two types of first high‐order modes: the first high‐order even mode and the first high‐order odd mode. A two‐port feeding structure is designed to feed the SSPP TL. When the signal is fed from port 1, the energy travels through the substrate integrated waveguide and eventually excites the even mode on the SSPP TL, leading to vertically polarised radiation. Conversely, when the signal is input from port 2, the energy travels through the stripline‐to‐slotline transition and eventually excites the odd mode on the SSPP TL, generating horizontally polarised radiation. According to the measured results, a 54.6% overlapping bandwidth is obtained. The horizontal and the vertical polarisations achieve a maximum gain of 14.7 and 12.2 dBi, respectively.

An inverted-L monopole radiating element is proposed for antenna-in-package modules at the 151.5-164 GHz band. Its radiation pattern is half-isotropic and is well-suited for phased arrays for mobile communications. The ideal inverted-L monopole is analyzed and initial design parameters are found. A radiating element structure designed for planar technology is proposed, which consists of eight copper layers and is fed by a stripline. Impedance matching and fabrication constraints are taken into consideration when designing the structure. An array is designed and fabricated with the same size and technology as the module. To prove its scanning capabilities, a scaled-up version of the array is fabricated and measured at 28 GHz. The beam coverage of the proposed arrays is very high, able to cover 80% with a realized gain of 10 dBi by using just 2 modules.

This paper proposes an all‐metal wideband circularly polarized (CP) single‐patch antenna based on TM11 mode. The conventional square patch is divided into four small square patch units by loading metal shorting walls under the two vertical centerlines. The shorting walls are windowed to facilitate coupling between the adjacent units. When the TM11 mode is excited, the coupling windows not only distribute energy but also provide the 90° phase difference required for CP radiation. An additional feeding network is not required, and its profile is less than 0.05λ0 (λ0 is the free space wavelength at the center frequency). Three minima in the axial ratio (AR) response are present. The results show that right‐hand circularly polarized (RHCP) radiation is achieved. The measured 3 dB AR bandwidth is 6.9%, ranging from 1.52 to 1.62 GHz, and the RHCP realized peak gain is 7.72 dBic. An all‐metal construction suitable for satellite communication systems is designed that has superior performance in harsh space environments. [ABSTRACT FROM AUTHOR]

A planar antenna with dual‐linearly polarised end‐fire radiation is proposed. A tapered double‐sided symmetrical spoof surface plasmon polariton (SSPP) transmission line (TL) with tilted unit cells is proposed. The SSPP TL can operate in two types of first high‐order modes: the first high‐order even mode and the first high‐order odd mode. A two‐port feeding structure is designed to feed the SSPP TL. When the signal is fed from port 1, the energy travels through the substrate integrated waveguide and eventually excites the even mode on the SSPP TL, leading to vertically polarised radiation. Conversely, when the signal is input from port 2, the energy travels through the stripline‐to‐slotline transition and eventually excites the odd mode on the SSPP TL, generating horizontally polarised radiation. According to the measured results, a 54.6% overlapping bandwidth is obtained. The horizontal and the vertical polarisations achieve a maximum gain of 14.7 and 12.2 dBi, respectively. [ABSTRACT FROM AUTHOR]

Abstract In this article, a novel design method is proposed based on characteristic mode theory (CMT). Based on the proposed method, a linearly polarised dual‐band wearable antenna with double‐layered substrates sandwiched by three layers of copper circle patches is designed and optimised step by step. The structure and excitation position of the antenna are obtained by progressively tailoring a classical circle patch antenna. Firstly, the characteristic mode analysis is performed on the middle‐layer planar circle patch to find the modes that can be excited in the designed frequency band. Secondly, the configuration of the middle layer is adjusted step by step based on the modal current distributions to realise the mode shift. Then, the top circle patch is changed to a metasurface to increase the number of modes and expand the mode bandwidth. Finally, the location of the excitation port is selected based on the modal electric fields to successfully obtain the desired performance of the antenna. The prototype of the proposed antenna with a radius of 2.6 cm fed by a single probe is fabricated and experimentally verified. The antenna operates in the 2.45 and 5 GHz bands, and the measured 10 dB impedance bandwidths on the two bands are 1.2% and 39.7%, respectively, which agrees well with the expectation predicted by the CMT. It should be noted that the desired antenna performance is achieved by step‐by‐step derivation using the CMT, rather than applying the theory to illustrate the working principle of antennas. The proposed design method can be broadly employed to various antenna designs.

Abstract Currently, no publicly available comprehensive set of specifications exists for the design of ground‐penetrating radar antennas. Specifications are presented and derived for the design of a ground‐penetrating radar antenna based on the antenna's interaction with the rest of the radar system. Typically, ground‐penetrating radar antenna engineers are given basic parameters such as gain and bandwidth to design an antenna. An antenna can be designed to meet those specifications but may not perform well in a ground‐penetrating radar imaging system. By considering the whole system, including the operation parameters, expected targets, and signal processing algorithms, we can constrain the less‐commonly considered performance aspects of an antenna to perform more reliably in a deployment. We propose quantitative specifications for the antenna's coupling, beamwidth, boresight radar cross‐section, pulse integrity, residual ringing, and front‐to‐back ratio. Meeting these antenna specifications will decrease the probability that a deficiency in the antenna design impacts the radar's image output. Finally, a summarised design equation table that will be helpful in the ground‐penetrating radar antenna community at large is offered.

Abstract The advancement of communication and radar systems has triggered the demand for in‐band full‐duplex (IBFD) operation. IBFD is regarded as one of the most outstanding technologies in terms of its ability to improve spectral efficiency and data rate. IBFD operation has the potential not only to enable communication or radar systems separately, but to help realising radar sensing and communication at the same time, known as Joint Communication and Sensing (JC&S) technology. In realisation of IBFD and JC&S systems, self‐interference (SI) is the key challenge for antenna designers. In this article, a comprehensive survey on SI reduction techniques in the antenna domain is provided and the advantages and disadvantages of each technique are studied. SI reduction techniques have been proposed separately but an elaborated review of relevant techniques with a comparative study has not been presented yet. For the first time, a systematic comparative study of different SI reduction techniques is graphically presented to cover a comparison based on isolation, gain, and impedance bandwidth in terms of before and after SI reduction techniques. Moreover, this study also explores how antenna isolation characteristics vary with respect to the thickness and the permittivity of the substrate without any SI reduction technique.

Abstract A low‐profile patch antenna with dual‐polarisation and high gain is proposed in this study. It contains a primary radiator, a secondary radiator, and a planar feed network. The primary and secondary radiators are square patches placed 5 mm from each other. Two planar feed networks are electrically connected with the primary radiator through the stepped impedance transformer, providing equal amplitude and 180° phase shift signals. These two feed networks are settled in different layers to weaken the coupling effect. The resonance generated by the primary radiator is merged with the one by the secondary radiator, covering the 3.3–3.6 GHz band. Benefiting from the differential feed method, antenna specifications such as port isolation and cross‐polarisation discrimination (XPD) are ideal. Moreover, as the primary radiator is fed by planar microstrip, the overall height can be reduced, and the gain can be enhanced. Finally, a 2 × 2 subarray is investigated. Desirable results show that the proposed antenna is suitable for application in Massive Multiple Input and Multiple Output (MIMO) systems.

Optimization of Josephson oscillators requires a quantitative understanding of their microwave properties. A Josephson junction has a geometry similar to a microstrip patch antenna. However, it is biased by a dc current distributed over the whole area of the junction. The oscillating electric field is generated internally via the ac-Josephson effect. In this work, I present a distributed, active patch antenna model of a Josephson oscillator. It takes into account the internal Josephson electrodynamics and allows for the determination of the effective input resistance, which couples the Josephson current to cavity modes in the transmission line formed by the junction. The model provides full characterization of Josephson oscillators and explains the origin of the low radiative power efficiency. Finally, I discuss the design of an optimized Josephson patch oscillator capable of reaching high efficiency and radiation power for emission into free space.

Frequency pulling technique (FPT) is a recently developed method for increasing the bandwidth (BW) of microstrip antennas. It is based on the insertion loss methodology used for the design of bandpass filters. Namely, to apply this technique, the resonators in a bandpass filter are replaced with antennas that have identical equivalent resonant circuits. Also, all the equivalent resonant circuits can represent symmetrical feeding points of a single antenna. Therefore, when these circuits are properly connected in accordance with the FPT rules, they create a matching network that increases the BW of a single antenna. However, prior studies on this method are limited to (1) narrowband antenna designs, (2) antennas with feeding points located at the same plane, and (3) feeding networks implemented as single feeding lines (e.g., microstrip lines) which have introduced several limitations and design complexities. In this work, we address these challenges by (1) extending FPT to wideband designs, (2) using feeding points located at different planes, and (3) designing feeding networks as unequal power dividers. Such networks not only simplify the design complexities associated with the traditional approach but also offer the capability to apply FPT to non-planar designs (e.g., 3D antenna configurations). To demonstrate the latter, we properly engineer a triangular tapered slot antenna, feeding it with a coupled microstrip line. As a result, the bandwidth of our modeled antenna increases from 34.51% to 78.25%, demonstrating excellent agreement between simulated and measured results.

Modern communication systems require an antenna with miniaturized size and large bandwidth with high data rate. In this article, a circular monopole antenna is presented with hexagonal patch on both sides of microstrip feedline and an I- shaped rectangular slot etched at the center of feedline to provide impedance matching. The modified loaded ground reduces the coupling between ground plane and radiation patch. This antenna has compact dimension of 30 mm × 25 mm with electrical size of 0.25λ × 0.20λ. This antenna has been designed and simulated in HFSS commercial software and fabricated on FR4 substrate of thickness 1.6 mm with relative permittivity 4.4, loss tangent of 0.02. The experimental results are compared with simulated one, which are in close agreement. It attains a frequency band ranging from 2.4 to 56.6 GHz with reflection coefficient <−10, percentage bandwidth of 183.72%, Bandwidth Ratio (BR) 23.58:1, and Bandwidth Dimension Ratio (BDR) of 3674.40. The peak gain and radiation efficiency of this antenna is 12.77 dBi and 98.82% at 45.84 and 5.6 GHz respectively. Time domain analysis has been done, which proclaims that the proposed antenna has SWB characteristics. It may be useful for high data rate transmission, medical imaging, and other SWB applications. [ABSTRACT FROM AUTHOR]

In this article, a novel design method is proposed based on characteristic mode theory (CMT). Based on the proposed method, a linearly polarised dual‐band wearable antenna with double‐layered substrates sandwiched by three layers of copper circle patches is designed and optimised step by step. The structure and excitation position of the antenna are obtained by progressively tailoring a classical circle patch antenna. Firstly, the characteristic mode analysis is performed on the middle‐layer planar circle patch to find the modes that can be excited in the designed frequency band. Secondly, the configuration of the middle layer is adjusted step by step based on the modal current distributions to realise the mode shift. Then, the top circle patch is changed to a metasurface to increase the number of modes and expand the mode bandwidth. Finally, the location of the excitation port is selected based on the modal electric fields to successfully obtain the desired performance of the antenna. The prototype of the proposed antenna with a radius of 2.6 cm fed by a single probe is fabricated and experimentally verified. The antenna operates in the 2.45 and 5 GHz bands, and the measured 10 dB impedance bandwidths on the two bands are 1.2% and 39.7%, respectively, which agrees well with the expectation predicted by the CMT. It should be noted that the desired antenna performance is achieved by step‐by‐step derivation using the CMT, rather than applying the theory to illustrate the working principle of antennas. The proposed design method can be broadly employed to various antenna designs. [ABSTRACT FROM AUTHOR]

Currently, no publicly available comprehensive set of specifications exists for the design of ground‐penetrating radar antennas. Specifications are presented and derived for the design of a ground‐penetrating radar antenna based on the antenna's interaction with the rest of the radar system. Typically, ground‐penetrating radar antenna engineers are given basic parameters such as gain and bandwidth to design an antenna. An antenna can be designed to meet those specifications but may not perform well in a ground‐penetrating radar imaging system. By considering the whole system, including the operation parameters, expected targets, and signal processing algorithms, we can constrain the less‐commonly considered performance aspects of an antenna to perform more reliably in a deployment. We propose quantitative specifications for the antenna's coupling, beamwidth, boresight radar cross‐section, pulse integrity, residual ringing, and front‐to‐back ratio. Meeting these antenna specifications will decrease the probability that a deficiency in the antenna design impacts the radar's image output. Finally, a summarised design equation table that will be helpful in the ground‐penetrating radar antenna community at large is offered. [ABSTRACT FROM AUTHOR]

The advancement of communication and radar systems has triggered the demand for in‐band full‐duplex (IBFD) operation. IBFD is regarded as one of the most outstanding technologies in terms of its ability to improve spectral efficiency and data rate. IBFD operation has the potential not only to enable communication or radar systems separately, but to help realising radar sensing and communication at the same time, known as Joint Communication and Sensing (JC&S) technology. In realisation of IBFD and JC&S systems, self‐interference (SI) is the key challenge for antenna designers. In this article, a comprehensive survey on SI reduction techniques in the antenna domain is provided and the advantages and disadvantages of each technique are studied. SI reduction techniques have been proposed separately but an elaborated review of relevant techniques with a comparative study has not been presented yet. For the first time, a systematic comparative study of different SI reduction techniques is graphically presented to cover a comparison based on isolation, gain, and impedance bandwidth in terms of before and after SI reduction techniques. Moreover, this study also explores how antenna isolation characteristics vary with respect to the thickness and the permittivity of the substrate without any SI reduction technique. [ABSTRACT FROM AUTHOR]

A low‐profile patch antenna with dual‐polarisation and high gain is proposed in this study. It contains a primary radiator, a secondary radiator, and a planar feed network. The primary and secondary radiators are square patches placed 5 mm from each other. Two planar feed networks are electrically connected with the primary radiator through the stepped impedance transformer, providing equal amplitude and 180° phase shift signals. These two feed networks are settled in different layers to weaken the coupling effect. The resonance generated by the primary radiator is merged with the one by the secondary radiator, covering the 3.3–3.6 GHz band. Benefiting from the differential feed method, antenna specifications such as port isolation and cross‐polarisation discrimination (XPD) are ideal. Moreover, as the primary radiator is fed by planar microstrip, the overall height can be reduced, and the gain can be enhanced. Finally, a 2 × 2 subarray is investigated. Desirable results show that the proposed antenna is suitable for application in Massive Multiple Input and Multiple Output (MIMO) systems. [ABSTRACT FROM AUTHOR]

Due to the orthogonality, multiple orbital angular momentums (OAMs) have great potential for increasing communication capacity and improving imaging resolution. In this work, a general N‐arm Archimedean spiral antenna (ASA) synthesis method is proposed for generating broadband vortex waves carrying multiple OAMs. In the proposed method, the theoretical formulas of the whole OAM modes based on the improved current band theory for N‐arm ASA and the maximum common bandwidth of each N‐adjacent OAM mode are presented. The performance of the proposed method is verified by simulated results of three‐arm ASA, as well as simulated results and measured results of four‐arm ASA. The measured results show that the four‐arm ASA generates vortex waves carrying OAM modes of l = 0, 1, 2, 3 in 0.6–3, 1.4–3.8, 2.3–4.1 and 2.6–4.5 GHz. And the maximum common bandwidth of the four generated OAM modes is 2.6–3 GHz, which satisfies the design requirement of OAM's practical application. [ABSTRACT FROM AUTHOR]

Multipole expansions are an essential analysis tool in the foundations of the descriptions of the electromagnetic fields radiated by electric and magnetic sources. Nevertheless, practical antenna systems generally rely on them as an academic explanation, not as a fundamental building block. An overview of the recent surge in interest in multipole sources and their fields to achieve useful radiated and scattered fields with, for example, high directivities in preferred directions is given. Topics include Huygens sources, dielectric-based Mie-tronics, edge-singularity multipoles, and exotic metamaterial-inspired superdirective lenses and radiators. While there has been a never-ending stream of physics publications, little has happened in the engineering electromagnetics community. I will try to answer the title with examples that may stimulate interest in the field.

Transistor laser can drive recent innovative technologies like optical antennas and rectennas. To this end, this semiconductor device requires an accurate electromagnetic model capable of determining the antenna characteristics like radiation pattern, directivity, gain, bandwidth, and polarization. Nonetheless, the current semiconductor models of transistor laser describe the absorption and emission of light mainly by simplified expressions and circuit models. These models usually overlook the actual physical geometry and full-wave light-emitting analysis of the device. In this article, a comprehensive computational electromagnetic modeling and characterization is presented for transistor laser. The existing semiconductor and electromagnetic equations are reorganized in a systematic fashion, coupled, and solved numerically to get the electromagnetic field components emitted or absorbed by the device. These fields determine the radiation pattern, directivity, gain, bandwidth, and polarization of transistor laser in transmit and receive modes. The equations involved in the above electromagnetic model are the Poisson and continuity equations incorporating radiative and non-radiative recombination rates, the vector magnetic potential equation interacting with the Hamiltonian operator of electrons in valance and conduction bands, the equation of the dielectric properties fluctuations of semiconductor layers, and the Poynting vector determining the power flow. The constructed model demonstrates agreement with the general performance of the device in experimental reports.

This paper first examines and corrects Storer’s theory of circular loop antennas, and then investigates theoretically the proposed $\Omega$ -shaped loop-dipole antenna. Special emphasis is given to the analysis of the effect of the higher-order terms of the Fourier series as a remainder on the current distribution, input impedance, and radiation patterns of the thin-wire circular loop antenna. It is found that the remainder must be included in the calculation of the current distribution and input impedance but can be neglected to simplify the calculation of far-field radiation. Then, a theoretical model is proposed to analyze the radiation fields, directivity, and input impedance of the proposed $\Omega$ -shaped loop-dipole antenna based on the loop and dipole antennas’ theories. Analytical expressions for the radiation fields, directivity, and input impedance of the $\Omega$ -shaped loop-dipole antenna are derived. The theoretical and numerical results are compared for the $\Omega$ -shaped loop-dipole antennas of practical interests. They are in good agreement.

Infinite periodic arrays of antennas that can be individually described by means of spherical modes are analyzed starting from the generalized scattering matrix (GSM) of an isolated element. After computing the GSM of an isolated element with the finite-element method (FEM), a fast postprocessing can be carried out to calculate the response of the element in an infinite array environment by using addition theorems for spherical modes. For this purpose, an efficient computation of lattice sums of spherical harmonics is used. The main advantage of this method is that the antenna is analyzed only once whatever the array lattice or scan angle. In addition, fast frequency analysis can be performed since the starting point is the computation of the isolated antenna with the FEM, which is suitable for fast frequency sweep. The active reflection coefficient and the embedded radiation pattern of the infinite periodic array are calculated for several examples to show the capabilities of the proposed method. [ABSTRACT FROM AUTHOR]

A set of new formulations derived from the cavity model (CM) that significantly improve the design of cylindrical single probe-fed circularly polarized rectangular microstrip antennas (CPRMAs) are presented in this article. Comprehensive analysis shows that differentiation of the dominant modes effective loss tangents in the far-field expressions gives rise to new closed-form design equations suitable for electrically thin antennas, extending the applicability and improving the CM accuracy for electrically small and large radii cylinders. Furthermore, a function is proposed to estimate the minimal number of significant terms needed in the far-field infinite series to portray the fields radiated by the antenna accurately. The proposed formulations are also used as part of an iterative CM-based algorithm that fully solves the issue of synthesizing a cylindrical CPRMA for a user-defined input impedance. Several antenna examples are compared to full-wave simulations to demonstrate the algorithm’s accuracy. To validate the proposed formulations, a right-hand circularly polarized cylindrical antenna prototype is designed and built to operate at 1.575 GHz over a cylinder with a radius of 25 mm. Comparisons between theoretical and experimental results show excellent agreement. [ABSTRACT FROM AUTHOR]

The whip antennas used for HF/VHF band communication on the vehicles or ships are generally larger in length and diameter. It would be of great significance if it could be easily hidden from microwave detection radar searches. Aiming at the lower RCS of whip antenna in X-band and maintaining the original impedance and radiation characteristics under high-power input, we propose a whip antenna integrating a novel curved artificial magnetic conductor (AMC) to achieve the RCS reduction in X-band. The backscattering of the cylinder can be dispersed by using the 180° phase difference cancellation principle of different AMC structures, and the mechanism is demonstrated by simulation and experiment. The measurements are in good agreement with the simulations, and the measurement results indicate that in the band of 8–12 GHz, the backward RCS is reduced by an average of 11.2 dBsm in VV polarization and by 10.2 dBsm in HH polarization. Moreover, the proposed whip antenna can be applied to high-power HF/VHF transmitting systems, and the withstand voltage can reach 15 kV (continuous output above 10 kW). This method has important theoretical significance and practical values for the whip antenna in practical engineering applications. [ABSTRACT FROM AUTHOR]

This article develops a broadband absorber by fully using the radiation features of monopole antennas for ultrawide-angle absorption application. A unit cell (UC) based on monopole antennas is proposed, and its working polarization is analyzed with the antenna reciprocity method and image theory. A wide-angle impedance matching layer is also introduced to further enhance the absorption at large angles. The optimized monopole-based UC reveals 90% absorptivity from 5.5–14.76 GHz at the incident angle of 80°. To the best of our knowledge, this is the first time to report an absorber that can work perfectly under such ultrawide angles in a broadband manner. An 11 × 36 array is configured and simulated to verify the effectiveness of the monopole-based UC. The monostatic and bistatic scattering are both reduced significantly as well as other diffuse scattering directions from the simulated results. A prototype of 110 mm × 360 mm is fabricated and measured. Time gating methods are adopted to diminish the direct coupling effect. The measurements are in good agreement with the full-wave simulation results. [ABSTRACT FROM AUTHOR]

A magnetic Yagi-Uda antenna applying higher order mode in millimeter-wave (mm-Wave) band with vertically polarized endfire radiation is proposed in this article. Surface wave mode analysis is applied to spot TE mode for magnetic Yagi-Uda antenna in contrast to TM mode for electric Yagi-Uda antenna. A modified structure evolved from conventional U-shaped cavity is used to address the reversed current issue for higher order mode, which exhibits a more uniform phase distribution at the Yagi-Uda array end. Then, a composite end-feeding structure with reflector integrated is further introduced to minimize its parasitic effects for practical antenna design in mm-Wave band. To validate the design, a prototype with a size of 2.7 $\lambda _{\mathbf {0}}\times1.25\lambda _{\mathbf {0}}\times0.088\lambda _{\mathbf {0}}$ is fabricated and tested. It can achieve anendfiregain of 8–11 dBi within 24–26 GHz with –10 dB impedance band covering an even wider frequency range. The measured front-to-back ratio (FBR) is larger than 16.1 dB. Vertically polarized radiation is realized with cross-polarization level lower than –20 dB atendfiredirection. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surfaces (RISs) have attracted major attention in the last few years, due to their useful characteristics. An RIS is a nearly passive thin surface that can dynamically change the reradiated field and can therefore realize anomalous reflection, refraction, focalization, or other wave transformations for engineering the radio propagation environment or realizing novel surface-type antennas. Evaluating the performance and optimizing the deployment of RISs in wireless networks need physically consistent frameworks that account for the electromagnetic characteristics of dynamic metasurfaces. In this article, we introduce a general macroscopic model for evaluating the scattering from an RIS. The proposed method decomposes the wave reradiated from an RIS into multiple scattering contributions and is aimed at being embedded into ray-based models. Since state-of-the-art ray-based models can already efficiently simulate specular wave reflection, diffraction, and diffuse scattering but not anomalous reradiation, we enhance them with an approach based on Huygens’ principle and propose two possible implementations for it. Multiple reradiation modes can be modeled through the proposed approach using the power conservation principle. We validate the accuracy of the proposed model by benchmarking it against several case studies available in the literature, which are based on analytical models, full-wave simulations, and measurements. [ABSTRACT FROM AUTHOR]

For wireless communications using linear large-scale antenna arrays, we define a receiving coordinate system and parameterization strategy to facilitate the study of the impact of three-dimensional position and rotation of the arrays on the achievable spatial degrees of freedom (DoF) in line-of-sight (LOS) channels. An analytical framework based on spatial bandwidth analysis is developed, under which three elementary problems corresponding to three basic orthogonal receiving directions are investigated. For each of them, accurate, simple, and interpretable closed-form approximations for the achievable spatial DoF are derived, and the spatial region where a sufficient amount of spatial DoF is expected available is determined. The expressions can easily be integrated into large-scale system-level simulations. Some interesting and surprising observations are made from simulation studies based on the analytical results. For instance, the spatial bandwidth is shown to be approximately constant in almost the entire spatial multiplexing region. Moreover, in significant parts of this region, the optimal receive array orientation is not parallel with the transmitting array. [ABSTRACT FROM AUTHOR]

This article proposes an original structure of evanescent quadridge antenna (EQA) to conceive dual-polarized full-metal front-ends that can be used in active antennas (AAs) with wide field-of-view (FoV). An original design methodology is here proposed that allows to induce radiation from subwavelength squared apertures based on the use of evanescent and quadridge waveguides. The proposal is illustrated by means of a design with 4.5% bandwidth providing dual-circular polarization (CP) with good performance up to 50°-scanning even in the diagonal plane. For comparison purposes, a metallic benchmark is also proposed, which is based on the use of classical quadridge horns. Such comparative analysis allows to understand the superior performance of the proposed concept and its main advantage: it allows to avoid the excitation of the first high order mode in the squared quadridge aperture. The excitation of such spurious mode in the antenna is explained in terms of simple equivalent circuit models characterizing the aperture periodic discontinuity. [ABSTRACT FROM AUTHOR]

Abstract In this work, a symmetric pillbox antenna with low side lobes is designed, simulated and fabricated by using gap waveguide technology. The proposed antenna operates on the basis of the reflector antenna principle and provides a fan‐beam radiation pattern. In the proposed structure, the antenna aperture is loaded by a stepped discontinuity and a corrective pin to improve the side‐lobe level (SLL) and gain. The designed antenna impedance bandwidth (S11

This article studies differential rectangular laminated resonator antenna (LRA) theoretically and experimentally. A theoretical model is proposed to analyze the radiation characteristics of the differential rectangular LRA based on the waveguide excitation theory. Analytical expressions for the inner fields, modal coefficients, radiation fields, directivity, radiation efficiency, and gain are derived. For verification, a prototype of rectangular LRA differentially fed by L-probes is simulated, fabricated, and measured. Acceptable agreements among the calculated, simulated, and measured results are achieved. The theoretical analysis demonstrates that the differential operation can suppress the adjacent high-order modes near the dominant mode and results in low cross-polarization level and a more symmetric radiation pattern. The proposed theoretical model provides physical insight into the operating principle of rectangular LRA and facilitates the design of rectangular LRAs. [ABSTRACT FROM AUTHOR]

A new theory called Vivaldi nonuniform slot profile antenna (VNSPA) is developed based on the nonuniform transmission lines (NTLs) theory and applied to reduce the size of the predesigned compact ultrawide band (UWB) Vivaldi-tapered slot antenna (VTSA) without affecting its performance in terms of matching and bandwidth. Using this theory, 33% of the taper slot length is reduced, resulting in a novel compact UWB Vivaldi nonuniform slot antenna (VNSA). Furthermore, compactness is achieved by performing parametric studies on VNSA with a final 51.94% size reduction. MATLAB optimization codes, CST simulation, and prototype manufacturing and measurement are used to validate the new theory. The proposed antenna provides a measured S11 < −10.89 dB through 2.9–13.55 GHz with 2.91% and 5.8% bandwidth and maximum realized gain enhancement, respectively, as compared with VTSA’s results. The effectiveness of VNSPA theory is proven by comparing the simulated and measured findings of VNSA and VTSA. [ABSTRACT FROM AUTHOR]

For very low frequency (VLF: 3–30 kHz) space-borne transmitting systems, the antenna loading technology provides a new technical scheme in boosting the antenna efficiency by optimizing its current distribution and input impedance. This communication studies the theory of VLF linear antennas applied with the lumped loadings in the ionospheric plasma. By considering the influences of ordinary and extraordinary waves and using Kirchhoff’s laws, the integral equation of the antenna under the effect of lumped loadings in an ionospheric plasma is derived and calculated by the method of moments (MoM). Calculations indicate that after loading capacitance, the overall current of the antenna increases while the input impedance decreases. It is also found that loading resistance and inductance will make the antenna current smaller. Theoretical results are compared with those simulated by commercial software, and the agreement demonstrates the validity of the approach. By comparing the input impedances of loaded and unloaded antennas, we observed that loaded antennas are more efficient than unloaded ones when the capacitance is appropriately deployed. [ABSTRACT FROM AUTHOR]

In this article, the authors propose a lumped circuit methodology for the design of broadband stacked microstrip patch antennas fed through an aperture. First, an equivalent circuit (EC) is introduced for the antenna. The EC consists of an $LC$ series resonator modeling the feed plus two capacitively coupled $LC$ parallel resonators accounting for the radiating patches. Then, a deembedding procedure based on total least squares method is introduced to determine all the parameters of the antenna EC. Second, the circuit stage modeling the patches is designed as a second-order Chebyshev filter based on coupled resonators. Since the standard Chebyshev approach leads to circuit parameters that cannot be physically obtained in practice, a modified second-order quasi-Chebyshev design is presented, which can be physically implemented by stacking one conventional rectangular patch above one rectangular patch with both inner and meandering slots. The proposed methodology is used to design an antenna with over 30% bandwidth at a center frequency of 5.57 GHz. A prototype has been fabricated and measured, and good agreement has been found between simulations and experiments. [ABSTRACT FROM AUTHOR]

A prior-knowledge-guided deep-learning-enabled (PK-DL) synthesis method is proposed for enhancing the transmission bandwidth and phase shift range of metacells used for the design of metalens antennas. The algorithm of conditional deep convolutional generative adversarial network (cDCGAN) is utilized in the proposed deep-learning (DL) method. Prior knowledge, including well-known fundamental electromagnetic theorems and experience in antenna design, is purposely applied at the early stage of the proposed method to strategically guide and speed up the synthesis. The proposed intelligent method provides the design of pixelated metacells with high degrees of freedom so that the key performance of the synthesized metacells exceeds the existing limit of conventional design methods by generating a rich profusion of cell patterns. For example, the synthesized triple-layer metacell achieves the −1 dB phase shift range of 330° breaking the limit of 308° derived by existing techniques. The proposed synthesis method also provides the additional capability to flexibly control the phase shift not only at the center frequency but also over a frequency range of interest. A Ku-band metalens antenna formed with the synthesized metacells demonstrates the achieved 1 and 3 dB gain bandwidths increase by 52.2% and 42.6%, respectively, compared to the metalens antenna using the well-known Jerusalem cross (JC) metacells. The proposed method extends the capability for the synthesis of metacells and metalens antennas with enhanced performance. [ABSTRACT FROM AUTHOR]

Estimating the coupling properties between a radiating structure and other conductive elements, the field behavior of the radiating source is essential to know. One well-known classification of the field behavior are the field-regions around antennas, namely, the far-field, the radiating near-field, and the reactive near-field. The different kinds of near-fields are distinguished by the reactive and radiating parts of the electromagnetic field, whereas in the far-field region the field behaves as a plane wave in the direction of propagation. One way to describe these field characteristics is to use the complex Poynting vector, which defines the electromagnetic power flow. This work presents a Poynting-vector-based approach to classify and visualize the field behavior around simple radiators using numerical simulations. First, the approach is applied to simple antenna structures such as dipoles and loop antennas. Later, the introduced field regions are utilized to predict the coupling behavior of practical applications, the coupling between single elements of a linear antenna array, and the coupling behavior of an electrically large loop antenna. It could be shown that the introduced approach, defining a surface description of the boundary between the near-field regions, enables the possibility of predicting the coupling behavior between radiating structures. The introduced error estimator for the far-field also delivers knowledge about the far-field quality in different angular directions and distances. All simulations have been executed applying a one-dimensional partial element equivalent circuit method. [ABSTRACT FROM AUTHOR]

Monopulse feed antennas represent a crucial component in satellite communication systems, particularly for Low Earth Orbit (LEO) satellites. In this comprehensive review, we delve into the design principles, operational advantages, and diverse applications of monopulse feed antennas in LEO satellite communication. We explore the fundamental concepts of monopulse antenna theory, the factors influencing antenna performance, and the various configurations and implementations of monopulse feed antennas. Additionally, we discuss advanced techniques, optimizations, and emerging trends in monopulse feed antenna design and deployment for LEO satellite constellations. By elucidating the intricacies of monopulse feed antennas, this review aims to provide engineers, researchers, and enthusiasts with valuable insights into maximizing the potential of these antennas for enhancing satellite communication in LEO orbits. [ABSTRACT FROM AUTHOR]

This letter studies differential aperture-coupled rectangular laminated resonator antenna (LRA) theoretically and experimentally. A theoretical model is proposed to analyze the resonance and radiation characteristics of the differential aperture-coupled rectangular LRA based on mode matching method. Analytical expressions for the resonant frequencies, Q-factor, impedance bandwidth (BW), radiation fields, directivity, radiation efficiency and gain are first derived. For verification, three prototypes of rectangular LRA with different length-to-height ratios differentially fed by a coupling slot are simulated, fabricated, and measured. Acceptable agreements among the calculated, simulated, and measured results are achieved. The proposed theoretical model provides physical insight into the operating principle of aperture-coupled LRA, which can be applied to predict the performances of rectangular LRAs and to instruct the design of rectangular LRAs. [ABSTRACT FROM AUTHOR]

In this paper, the analysis of an UWB monopole antenna using the Theory of Characteristic Modes is presented. It starts from the modal study of an asymmetric dipole (structure 1), and then complements and compares it with a broadband monopole (structure 2), aiming to understand the operation principle of the proposed antenna. To achieve this, the electromagnetic properties of the structures are analyzed through the generation of its characteristic angles, modal radiation patterns, characteristic currents, and the power contribution percentage of each mode to the total radiated power, providing a vision on how the superposition of individual characteristic modes enables UWB operation. The prototype model is fabricated, and the measured results agree very well with the full-wave simulations results. The proposed prototype has a very low profile and operates in the frequency band from 2.8 GHz to exceed 10 GHz for a reflection coefficient S11 less than -10dB. [ABSTRACT FROM AUTHOR]

Abstract Three‐dimensional dipole arrays are normally used at the proximity of a reflective structure. Filamentary short‐circuited dipoles are proposed to model the effect of the reflector structure. The computational burden is significantly reduced by using mutual impedance matrices. An analytical method of modelling the effect of the cylindrical reflector in a three‐dimensional cylindrical geometry of dipole antenna arrays is introduced both for direction finding and beamforming applications in the presence of mutual coupling. The results of the implementation of the MUSIC (multiple signal classification) direction‐finding algorithm show that the proposed model for accounting the cylindrical reflector, in the presence of a mutual coupling effect, has the required efficiency and reduced root‐mean‐square‐error (RMSE). Monte‐Carlo simulations for the beamforming algorithm are conducted to evaluate the signal‐to‐interference ratio (SIR) values in the presence of a cylindrical reflector and the results show that the model has the desired performance. The whole process of beamforming and pattern generation has been verified through high‐frequency structural simulator (HFSS) simulation. The simplicity, adequate precision and low computational cost of this method can be appropriately used in the cylindrical reflector/scatterer in three‐dimensional geometries, especially for base station applications.

Abstract Tropospheric scatter is a promising method for over‐the‐horizon propagation. Transmission loss caused by the three mainstream troposcatter mechanisms is analysed, namely turbulent incoherent scattering theory, coherent reflection by stable layers theory, and incoherent reflection by irregular layers theory. Then an experiment is conducted to explore the relationships among the three mechanisms. Based on this experiment, the troposcatter transmission loss prediction model is established in different climate zones by a particle swarm optimisation algorithm and experimental data from the global troposcatter databank. The simulation shows that this model is more effective than the existing International Telecommunication Union‐Radiocommunication Sector (ITU‐R) P.617, P.452, and P.2001. Furthermore, by analysing the training parameters' proportion of the new model in different climate zones, the specific composition of three troposcatter mechanisms can be obtained.

The techniques on the generation of multiple solutions in shaped-beam pattern synthesis are standardly focused on the use of patterns with complex nature as input. Otherwise, in order to derive a symmetric pure real distribution from the canonical pattern synthesis techniques, a generation of a pure-real pattern has to be imposed. In the present work, the exploitation of the multiplicity of the shaped pattern generated by this symmetric pure real distribution is proposed, without constraining the solutions to necessarily meet the pure-real pattern requirement. Therefore, an increase on the degrees of freedom is produced and a greater number of continuous distributions (presenting different natures) is achieved, by omitting the restrictions found in the state-of-the-art methodologies. Thus, a general multiplicity of solutions can be reached and the design protocol can increase its number of alternatives for facing different feeding network structures. In such a way, this article is devoted to illustrate the improvements in terms of number of feasible solutions reached by the general method, including alternative symmetric pure real distributions as input within the procedure. In this manner, two different approaches, constraining the pattern to present the same number of ripples or a similar main beam width, are discussed. Examples of both Taylor distributions linear and circular are illustrated.