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Abstract The oversized TE11 mode bend is able to make the transmission direction of electromagnetic wave to turn 90°, and it is one of the key components in the high‐power microwave system. The mode coupling characteristics between the TE11 and parasitic modes under two different polarisations in the bending waveguide are analysed, and it is found that the TE11 suffers less interferences from parasitic modes when its polarisation direction is perpendicular to the bending plane, and the corresponding 90° TE11 bend is easier to realise high performance. To verify this analysis, an oversized 90° TE11 bend waveguide working at 10 GHz is designed, and its structural length is only 7.5 times the central working wavelength. Simulated results indicate that its relative bandwidth is 15.6% when the transmission efficiency is over 98%, and its maximum power handling capacity reaches 5.6 GW at short microwave pulse duration (less than 100 ns). The S‐parameters indicate that its S21 is about −0.1 dB from 9.5 to 10.5 GHz, and its S11 is under −25 dB in the same frequency range. Meanwhile, the high power test indicates that the bend works stably when the injected power is 3 GW.

The oversized TE11 mode bend is able to make the transmission direction of electromagnetic wave to turn 90°, and it is one of the key components in the high‐power microwave system. The mode coupling characteristics between the TE11 and parasitic modes under two different polarisations in the bending waveguide are analysed, and it is found that the TE11 suffers less interferences from parasitic modes when its polarisation direction is perpendicular to the bending plane, and the corresponding 90° TE11 bend is easier to realise high performance. To verify this analysis, an oversized 90° TE11 bend waveguide working at 10 GHz is designed, and its structural length is only 7.5 times the central working wavelength. Simulated results indicate that its relative bandwidth is 15.6% when the transmission efficiency is over 98%, and its maximum power handling capacity reaches 5.6 GW at short microwave pulse duration (less than 100 ns). The S‐parameters indicate that its S21 is about −0.1 dB from 9.5 to 10.5 GHz, and its S11 is under −25 dB in the same frequency range. Meanwhile, the high power test indicates that the bend works stably when the injected power is 3 GW. [ABSTRACT FROM AUTHOR]

The authors design and experimentally analyse an anisotropic metasurface for the simultaneous conversions of linear cross and circular polarisations in the C and partial X bands. The proposed compact structure utilises a dual‐cut square‐ring resonator and a square patch on an FR4 substrate above a ground plane. The full‐wave simulations exhibit over 92% efficiency in cross‐conversion over a fractional bandwidth (BW) of 52.3%. The proposed metasurface efficiently converts linear to circular polarisation in two different bands, achieving left‐hand circularly polarised and right‐hand circularly polarised efficiencies exceeding 93% and 89%, respectively. The compact unit‐cell with dimension 0.22λ × 0.22λ attains stable polarisation transformation efficiency rates exceeding 80% up to 40° incident angles. The design is adaptable for efficient wide BW across both lower and higher (millimetre‐wave) frequencies through scaling. A prototype of the proposed polarisation converter (PC) was realised and validated effectively in measurements, aligning well with simulations. This PC features a novel and simple structure with multifunctional wideband operation, stable incident angle output, polarisation insensitivity, and scalability, making it an efficient front‐end for various radio frequency applications, including polarisation control and polarisation transformers. [ABSTRACT FROM AUTHOR]

Abstract A two‐layered wideband single‐fed circularly polarised (CP) antenna is presented by the authors. A single‐fed corner‐truncated square patch with four identical rectangular matching branches acts as a bottom‐driven patch to generate CP radiation. To broaden the 3‐dB axial ratio (AR) bandwidth, a similar patch with a larger size is loaded atop the driven patch as a parasitic patch. The measured results show that the proposed CP antenna has a 17.9% impedance bandwidth from 2.13 to 2.55 GHz and an 11% 3‐dB AR bandwidth from 2.15 to 2.4 GHz, respectively. The measured total gain is 7.1 dBic. The results indicate that the proposed antenna is a good candidate for Wireless Local Area Network band applications.

Abstract The authors investigate the feasibility of forming a composite Gaussian waveform in the high‐frequency region for jetfighter class targets with a high potential to combat the noise effect and the late‐time signature onset ambiguity when estimating the target resonance signature. The excitation waveform comprises a composite of modulated carriers with fractional bandwidth and amplitude adapted to lower specular content while enhancing the radar target resonance content in the radar return, subsequently increasing the likelihood of extracting the resonance parameters more accurately. The validation of improvement in the resonance signature requires finding the error between the excitation frequencies and the extractable resonant frequencies in the return echo and, second, the similarity or resemblance between the original echo waveform and the reconstructed waveform by the estimated resonance set. The results presented the robustness rate in instantaneous, average, and overall fashion. In conclusion, a fractional bandwidth between 0.3 and 0.4 would significantly improve the signature overall robustness with a circular then slant scattering polarisation set outperforming the horizontal and vertical directions. Also, excluding the signal's high and low energy portions further enhance the accuracy of the estimated resonance mode set.

The authors investigate the feasibility of forming a composite Gaussian waveform in the high‐frequency region for jetfighter class targets with a high potential to combat the noise effect and the late‐time signature onset ambiguity when estimating the target resonance signature. The excitation waveform comprises a composite of modulated carriers with fractional bandwidth and amplitude adapted to lower specular content while enhancing the radar target resonance content in the radar return, subsequently increasing the likelihood of extracting the resonance parameters more accurately. The validation of improvement in the resonance signature requires finding the error between the excitation frequencies and the extractable resonant frequencies in the return echo and, second, the similarity or resemblance between the original echo waveform and the reconstructed waveform by the estimated resonance set. The results presented the robustness rate in instantaneous, average, and overall fashion. In conclusion, a fractional bandwidth between 0.3 and 0.4 would significantly improve the signature overall robustness with a circular then slant scattering polarisation set outperforming the horizontal and vertical directions. Also, excluding the signal's high and low energy portions further enhance the accuracy of the estimated resonance mode set. [ABSTRACT FROM AUTHOR]

A two‐layered wideband single‐fed circularly polarised (CP) antenna is presented by the authors. A single‐fed corner‐truncated square patch with four identical rectangular matching branches acts as a bottom‐driven patch to generate CP radiation. To broaden the 3‐dB axial ratio (AR) bandwidth, a similar patch with a larger size is loaded atop the driven patch as a parasitic patch. The measured results show that the proposed CP antenna has a 17.9% impedance bandwidth from 2.13 to 2.55 GHz and an 11% 3‐dB AR bandwidth from 2.15 to 2.4 GHz, respectively. The measured total gain is 7.1 dBic. The results indicate that the proposed antenna is a good candidate for Wireless Local Area Network band applications. [ABSTRACT FROM AUTHOR]

Abstract Polarisation diversity radar enhances the performance of target detection. Time reversal exploits the multipath effect by adaptively matching propagation channels to improve the signal‐to‐noise ratio (SNR) and realise high detectability. This work combines polarisation diversity and time‐reversal technology to propose a time‐reversal detector suitable for a polarisation array radar. The maximum likelihood estimate is carried out for the time‐varying channel response to solve the channel mismatch problem, which may cause the degradation of time‐reversal performance. In addition, a conventional polarisation detector is developed under the same varying channel scenario to benchmark the time‐reversal detector, and furthermore, the SNR gain of the time‐reversal detector over the conventional detector is derived. Numerical simulations demonstrate the superiority of the time‐reversal detector. Both the polarisation detectors proposed can take advantage of the channel variations to improve the detectability, and the greater the energy brought by the channel changes, the better the detection performance achieved.

Abstract Circularly polarised multiple‐input‐output antennas embedded in wearable wireless devices attract importance in the individual security and beauty fabric modelling industry involving technology embedded on‐clothes wearables. A circularly polarised wideband is designed and analysed in the present design‐study where a wearable application uses a multiple‐input‐output. It adds 2 symmetric ‘Multi‐Input‐Multi‐Output’ antennas that are good looking design like a swan‐shaped, and the ground plane is similar to the shape of a swan. The designed novel antenna comprises a ground plane having a line feed and a rectangular inverted L‐type micro‐strip which is supporting circular polarisation. The antenna element is spanning at 3‐DeciBell (dB) Axial Ratio Band‐Width of 5.2–7.1 GHz and an impedance bandwidth (S11 less than or equal to −10 dB) of 3.6–13 GHz. The proposed antenna manifesting a channel capacity loss less than 0.2 b/s/Hz, and envelope correlation coefficient less than the value 0.02, total active reflective coefficient less than −10 dB, and diversity gain greater than the value of 9.96, Mean Effective Gain (also represented as MEG) ratio is within ±0.5 dB. There is a twin‐sense circular polarisation in this antenna and superior isolation between resonating elements (greater than 18). The proposed antenna for human tissues specimens is also discussed with its specific absorption rate (also pronounced as SAR) in different situations that pertain to the living body. The overall size of the proposed ‘Circularly Polarised’ textile ‘Multi‐Input‐Multi‐Output’ antenna is 34:5 × 42 × 1 mm3. Because of its textile layers, reasonable performance, and compact size, the designed ‘Multi‐Input‐Multi‐Output’ antenna may be useful for wearable applications. The presented novel antenna can be made unrecognisable with a beautiful swan‐shaped design that can simply comingle with the other designs of fabric (in the fashion dress). The simulated antenna was made‐up following regular and general manual techniques and verified in the proposed conditions. The corner‐to‐corner distance between the ‘Multi‐Input‐Multi‐Output’ antennas is 14.2 mm, and the achieved isolation is beyond 18 dB after suitable adjustments of the designed final antenna.

Abstract In the study, a miniaturised printed quadrifilar helix antenna (PQHA) with isoflux coverage and wide‐angle circular polarisation is presented. It is composed of a three‐stage stepped impedance spiral arm and open stubs. Each of the three‐stage spiral arms has different pitches and number of turns. For the last‐stage spiral arm, meander lines are used. The proposed PQHA features the characteristics of wide bandwidth, isoflux radiation, small size, and wide‐angle circular polarisation. Moreover, in order to feed the proposed PQHA, a miniaturised quad‐feed network is designed to provide equal amplitude signals with sequential orthogonal phases. For demonstration, a prototype is designed, fabricated, and measured. The overall size of the proposed antenna is 88 × 88 × 132 mm (0.44 λ0 × 0.44 λ0 × 0.66 λ0). The results show that isoflux radiation with a coverage of about ±60° is realised from 1.40 to 1.62 GHz (14.6%) while maintaining more than 10 dB return loss and larger than 200° 3‐dB axial ratio beamwidth.

Abstract A switchable polarisation conversion/in‐phase reflection metasurface (PCIPR‐MS) based on a Pin diode is proposed in this study. By changing the working state of the Pin diode, the PCIPR‐MS can be used as a polarisation conversion metasurface (PCM) and an artificial magnetic conductor (AMC), respectively. Furthermore, the designed PCIPR‐MS can be arranged into a checkerboard surface to integrate with the antenna, which means that the PCIPR‐MS can be flexibly switched to control the radiation and scattering characteristics of the antenna in a time‐sharing manner. The simulation results show that the 3‐dB axial ratio (AR) bandwidth is 4.31 to 6.14 GHz (35%) with the application of the AMC as the metal ground plane of the antenna in the radiation state, and the right‐hand circularly polarised (RHCP) gain is enhanced by more than 1.5 dB from 4.65 to 5.80 GHz in a low‐profile compared with the reference antennas. By using the PCM, phase cancelation is achieved in the scattering state of the antenna to realise the low‐RCS characteristics.

Abstract Single‐layer ultrathin absorber patch elements are analysed under normal and oblique incidence. A compensation technique for impedance variation with an angle of incidence (θ) is proposed. An equivalent‐circuit model is formulated that provides a realisation for the absorption response (in terms of resonance frequency and absorption ratio) of non‐complicated rectangular patch absorbers using simple equations. The design methodology proposed is based on using multiple subcells of simple patches to add another degree of freedom for the design equations and keep the ultrathin planar feature. Previously reported techniques realising a wide angle of incidence are applied for fair comparison with the proposed methodology. The developed structure features angular stability, polarisation insensitivity, and a planar non‐complicated configuration compared with that of structures reported in literature. Moreover, a prototype is fabricated and measured to validate the proposed approach.

Abstract Scattering of the E‐polarised plane electromagnetic wave from two different but of the same‐period all‐dielectric rectangular bar gratings on substrates is analysed using a volume‐integral‐equation (VIE) method. Here, VIE is a Fredholm integral equation of the second kind with unknown function being the electric field in the gratings regions. Discretisation of the VIE is performed by applying an entire‐domain Galerkin technique. The developed algorithm possesses guaranteed convergence, provides accuracy, and is easily controlled by the order of discretisation. Numerical results for frequency‐selective reflection, manipulation of light to propagate in prescribed directions, and the ultrahigh‐Q lattice‐modes resonances are presented and discussed.

Abstract Scattering and absorption of the H‐polarized plane wave by the infinite grating of flat graphene strips are considered in the environment met most frequently—on or at the surface of a dielectric‐slab substrate. The full‐wave meshless code is based on the analytical semi‐inversion using the Riemann–Hilbert problem solution. This leads to a Fredholm second‐kind matrix equation for the Floquet harmonic amplitudes that guarantees code convergence and provides easy control of computational error, which can be reduced to machine precision. The matrix elements are combinations of elementary functions, and therefore, the code is accurate and quite economical. This enables computation of the reflectance, transmittance, and absorbance as a function of the frequency in the wide band from static case to 10 THz. Numerical results show that such a metasurface with micrometre‐sized strips is a composite periodic open resonator. It is highly frequency‐selective thanks to the interplay of three types of natural modes—low‐Q slab, moderate‐Q plasmon strip, and ultra‐high‐Q lattice—that do not exist in the absence of the substrate. Varying the chemical potential of graphene, one can manipulate the electromagnetic characteristics of the metasurface at a fixed frequency from almost total transmission to almost total reflection.

Abstract A rigorous theory is developed for the multiple scattering analysis of an E− polarised plane wave from an ensemble of 2‐D slotted arbitrary cylinders. The Method of Analytical Regularisation, previously applied to the solution of scattering wave problems for isolated slotted cylinders, is generalised to problems incorporating ensembles of closed or slotted cylinders. Numerical calculations of the complex eigenvalues, Q− factors and resonant current densities are performed for various configurations of two slotted circular or elliptical cavities, focussing on an accurate assessment of differing peculiarities of the mutual resonant electromagnetic coupling.

Abstract The diffraction of an E‐polarized plane wave from two finite sinusoidal gratings is investigated by a rigorous approach, based on the Method of Analytical Regularization. This allows us to analyse the problem in a wide frequency band without limitations on the depth of the sinusoidal corrugation, the wave size of the gratings, or their relative location. The homogeneous version of the equations obtained is used for accurate computation of the complex eigenvalues in an open resonator of Fabry–Perot type with sinusoidally corrugated strips. In the calculations, two types of structures were used: one is formed by parallel translation of the sinusoidally corrugated strips and the other is obtained by rotation of one of the strips in the first structure. For each relative location of the corrugated strips, the resonance excitation of the structure by an obliquely incident E‐polarized plane wave is considered. Based on the calculation of the surface current density for different incidence angles, their specific values for optimal excitation of the complex modes are established.

Abstract The Cauchy method of analytical regularisation, first in full explanation, is used for the modelling of the plane wave scattering by a flat pre‐fractal system of impedance strips. It is based on a modification of the singular integral equation technique and the correct type of inversion formula of the simplest Cauchy singular integral equation. The approach is effective for the plane H‐polarised electromagnetic (or sonic) wave scattering problems. The principle of strict mathematical orderings of the pre‐fractal strip grating deals with a five‐parts class of perfect fractal sets, which is characterised by a variable positive fractal dimension. Considerable attention is devoted to the asymptotic model of the plane wave scattering by a sparsely filled grating, which has an explicit solution. This result is very important for verification of the mathematical models presented and testing of direct numerical methods. The scattered electromagnetic field in the far zone is successfully analysed with the aid of the asymptotic solution derived for electrically narrow strips.

Abstract The Carleman method of analytical regularization is used to model the plane E‐polarized electromagnetic wave scattering by flat grating of a finite number of impedance strips. It is based on a modification of the singular integral equation technique, the perturbation method and the Carleman inversion formula for the simplest logarithmically singular integral equation. Attention is focussed on the asymptotic model of the plane E‐polarized electromagnetic wave scattering by a sparsely filled impedance strip grating. In this case, the corresponding singular integral equation system has an explicit solution. This result is important to verify direct numerical methods. The scattered electromagnetic field in the far zone is successfully analysed with the aid of the asymptotic solution derived for electrically narrow strips.

Abstract Large scale (i.e.

Abstract Given that the discrimination between the two senses of circular polarisation (CP) has been reported for cascades of progressively rotated wire‐grids, the author investigates whether or not the progressive rotation of the elements of a cascade would be the fundamental reason for the cascade to discriminate between the two senses of CP. The author also investigates whether or not the particular progressive rotation that consists in aligning each element of the cascade with the polarisation of a normally incident CP plane wave would necessarily provide the maximum discrimination between the two senses of CP. It is shown that neither progressive rotation nor alignment are fundamental or optimal for CP discrimination. CP discrimination is shown to be achieved even when the physical geometry of the CP antenna does not match the screw that is traced in space by the CP wave which is meant to be received/transmitted by the CP antenna. This observation is important to avoid misunderstanding the mechanism that underlies the phenomenon of CP discrimination.

Abstract This study presents a simple and low‐profile cylindrical dielectric resonator antenna (CDRA) for the fifth‐generation (5G) band (3.5 GHz) with switchable polarization. The antenna can operate with linear or circular polarization (right‐handed circular polarization [RHCP] or left‐handed circular polarization [LHCP]) by changing the states of the PIN diodes below the CDRA, while keeping the same operating frequencies. The antenna operates at three modes (Mode 1, Mode 2, and Mode 3). It exhibits linear polarization in Mode 1, RHCP in Mode 2, and LHCP in Mode 3. The 10‐dB bandwidths of 750 MHz (3.1–3.85 GHz), 950 MHz (3.03–3.98 GHz), and 960 MHz (3.03–3.99 GHz) are noted for Mode 1, Mode 2, and Mode 3, respectively. The 3‐dB axial ratio bandwidth of 22.2% (3.09–3.86 GHz) and 21.4% (3.08–3.82 GHz) is achieved for Mode 2 and Mode 3, respectively. The reported antenna has high gain ( >5.25 dBi for all operating modes) and high radiation efficiency ( >79.8% for all operating modes). The proposed antenna is suitable for use in polarization diversity applications.

Abstract The interaction of radar signals with a planetary surface is critical for the utility of radar data. Herein, a power‐law roughness spectrum is used to model the roughness and an inhomogeneous vertical permittivity to describe the dielectrics from the surface of Mars. Numerical simulations of depolarised radar backscattering are then conducted. To gain a more complete picture of depolarised characteristics, a wide range of surface roughness is considered. Results reveal that the depolarised backscattering is sensitive to the dielectric profiles with –10 dB is observed. The polarization conversion ratio, the ratio of depolarisation to total polarization backscattering, is a sensitive indicator of dielectric profiles and roughness, and thus is useful in retrieving dielectric profile.

Abstract In the present study, a novel periodic planar leaky‐wave antenna (PLWA) was designed, simulated, and fabricated based on the substrate integrated waveguide (SIW) technology. The antenna can scan the main beam from around −60° to +20° continuously with complete suppression of open stopband (OSB) by the sweeping frequency from 9.2 to 14.1 GHz. The proposed structure was designed to have circular polarisation (CP) in the entire operating frequency range, where the broadside or centre frequency is 12.25 GHz. Antenna gain in the broadside frequency is around 13 dBi. The radiation efficiency of the structure is improved and equalised through broadside, which is around 80% in the frequency band of operation. Also, series and shunt analysis was applied to the proposed periodic PLWA in the fundamental TE10 mode. In the next step, the asymmetric was applied longitudinally and transversely to the proposed structure to achieve OSB elimination combined with circular polarised radiation simultaneously. The equivalent circuit of the proposed structure was extracted and, finally, the antenna was fabricated. Based on the results, excellent agreement was observed between the measured, modelled, and simulated results.

In the study, a miniaturised printed quadrifilar helix antenna (PQHA) with isoflux coverage and wide‐angle circular polarisation is presented. It is composed of a three‐stage stepped impedance spiral arm and open stubs. Each of the three‐stage spiral arms has different pitches and number of turns. For the last‐stage spiral arm, meander lines are used. The proposed PQHA features the characteristics of wide bandwidth, isoflux radiation, small size, and wide‐angle circular polarisation. Moreover, in order to feed the proposed PQHA, a miniaturised quad‐feed network is designed to provide equal amplitude signals with sequential orthogonal phases. For demonstration, a prototype is designed, fabricated, and measured. The overall size of the proposed antenna is 88 × 88 × 132 mm (0.44 λ0 × 0.44 λ0 × 0.66 λ0). The results show that isoflux radiation with a coverage of about ±60° is realised from 1.40 to 1.62 GHz (14.6%) while maintaining more than 10 dB return loss and larger than 200° 3‐dB axial ratio beamwidth. [ABSTRACT FROM AUTHOR]

A switchable polarisation conversion/in‐phase reflection metasurface (PCIPR‐MS) based on a Pin diode is proposed in this study. By changing the working state of the Pin diode, the PCIPR‐MS can be used as a polarisation conversion metasurface (PCM) and an artificial magnetic conductor (AMC), respectively. Furthermore, the designed PCIPR‐MS can be arranged into a checkerboard surface to integrate with the antenna, which means that the PCIPR‐MS can be flexibly switched to control the radiation and scattering characteristics of the antenna in a time‐sharing manner. The simulation results show that the 3‐dB axial ratio (AR) bandwidth is 4.31 to 6.14 GHz (35%) with the application of the AMC as the metal ground plane of the antenna in the radiation state, and the right‐hand circularly polarised (RHCP) gain is enhanced by more than 1.5 dB from 4.65 to 5.80 GHz in a low‐profile compared with the reference antennas. By using the PCM, phase cancelation is achieved in the scattering state of the antenna to realise the low‐RCS characteristics. [ABSTRACT FROM AUTHOR]

The Cauchy method of analytical regularisation, first in full explanation, is used for the modelling of the plane wave scattering by a flat pre‐fractal system of impedance strips. It is based on a modification of the singular integral equation technique and the correct type of inversion formula of the simplest Cauchy singular integral equation. The approach is effective for the plane H‐polarised electromagnetic (or sonic) wave scattering problems. The principle of strict mathematical orderings of the pre‐fractal strip grating deals with a five‐parts class of perfect fractal sets, which is characterised by a variable positive fractal dimension. Considerable attention is devoted to the asymptotic model of the plane wave scattering by a sparsely filled grating, which has an explicit solution. This result is very important for verification of the mathematical models presented and testing of direct numerical methods. The scattered electromagnetic field in the far zone is successfully analysed with the aid of the asymptotic solution derived for electrically narrow strips. [ABSTRACT FROM AUTHOR]

The diffraction of an E‐polarized plane wave from two finite sinusoidal gratings is investigated by a rigorous approach, based on the Method of Analytical Regularization. This allows us to analyse the problem in a wide frequency band without limitations on the depth of the sinusoidal corrugation, the wave size of the gratings, or their relative location. The homogeneous version of the equations obtained is used for accurate computation of the complex eigenvalues in an open resonator of Fabry–Perot type with sinusoidally corrugated strips. In the calculations, two types of structures were used: one is formed by parallel translation of the sinusoidally corrugated strips and the other is obtained by rotation of one of the strips in the first structure. For each relative location of the corrugated strips, the resonance excitation of the structure by an obliquely incident E‐polarized plane wave is considered. Based on the calculation of the surface current density for different incidence angles, their specific values for optimal excitation of the complex modes are established. [ABSTRACT FROM AUTHOR]

A rigorous theory is developed for the multiple scattering analysis of an E− polarised plane wave from an ensemble of 2‐D slotted arbitrary cylinders. The Method of Analytical Regularisation, previously applied to the solution of scattering wave problems for isolated slotted cylinders, is generalised to problems incorporating ensembles of closed or slotted cylinders. Numerical calculations of the complex eigenvalues, Q− factors and resonant current densities are performed for various configurations of two slotted circular or elliptical cavities, focussing on an accurate assessment of differing peculiarities of the mutual resonant electromagnetic coupling. [ABSTRACT FROM AUTHOR]

Scattering of the E‐polarised plane electromagnetic wave from two different but of the same‐period all‐dielectric rectangular bar gratings on substrates is analysed using a volume‐integral‐equation (VIE) method. Here, VIE is a Fredholm integral equation of the second kind with unknown function being the electric field in the gratings regions. Discretisation of the VIE is performed by applying an entire‐domain Galerkin technique. The developed algorithm possesses guaranteed convergence, provides accuracy, and is easily controlled by the order of discretisation. Numerical results for frequency‐selective reflection, manipulation of light to propagate in prescribed directions, and the ultrahigh‐Q lattice‐modes resonances are presented and discussed. [ABSTRACT FROM AUTHOR]

The Carleman method of analytical regularization is used to model the plane E‐polarized electromagnetic wave scattering by flat grating of a finite number of impedance strips. It is based on a modification of the singular integral equation technique, the perturbation method and the Carleman inversion formula for the simplest logarithmically singular integral equation. Attention is focussed on the asymptotic model of the plane E‐polarized electromagnetic wave scattering by a sparsely filled impedance strip grating. In this case, the corresponding singular integral equation system has an explicit solution. This result is important to verify direct numerical methods. The scattered electromagnetic field in the far zone is successfully analysed with the aid of the asymptotic solution derived for electrically narrow strips. [ABSTRACT FROM AUTHOR]

Scattering and absorption of the H‐polarized plane wave by the infinite grating of flat graphene strips are considered in the environment met most frequently—on or at the surface of a dielectric‐slab substrate. The full‐wave meshless code is based on the analytical semi‐inversion using the Riemann–Hilbert problem solution. This leads to a Fredholm second‐kind matrix equation for the Floquet harmonic amplitudes that guarantees code convergence and provides easy control of computational error, which can be reduced to machine precision. The matrix elements are combinations of elementary functions, and therefore, the code is accurate and quite economical. This enables computation of the reflectance, transmittance, and absorbance as a function of the frequency in the wide band from static case to 10 THz. Numerical results show that such a metasurface with micrometre‐sized strips is a composite periodic open resonator. It is highly frequency‐selective thanks to the interplay of three types of natural modes—low‐Q slab, moderate‐Q plasmon strip, and ultra‐high‐Q lattice—that do not exist in the absence of the substrate. Varying the chemical potential of graphene, one can manipulate the electromagnetic characteristics of the metasurface at a fixed frequency from almost total transmission to almost total reflection. [ABSTRACT FROM AUTHOR]

This study discusses the design of a low-profile metamaterial-based antenna consisting of a 3 × 5 array of Hilbert shaped unit cells organised as a rectangular patch. The antenna is backed by with a partial ground plane loaded with square electromagnetic band gap defects for energy harvesting applications in the context of ultra-wideband self-powered wearable wireless devices. The antenna is mounted on a 28 × 32 mm FR4 substrate, with a thickness of 0.394 mm, a relative permittivity of 4.2 and a loss tangent of 0.02. The antenna is also printed on a flexible solar panel for self-powered devices through solant–rectenna output terminals. The proposed solant–rectenna is found to cover the frequency range from 0.8 up to 10 GHz. The I–V characteristics of the solar panel are measured with and without the antenna structure to realize low shadowing effects. After that, the solant radiofrequency (RF) port is connected to a rectifier circuit to create a rectenna port that collects the RF energy and converts it to an output DC voltage at 0.915 GHz. It is found that the proposed rectenna provides an output DC voltage of 1.42 V with a conversion efficiency of 90%.

A circularly polarised (CP) monopulse waveguide antenna array for Ka‐band wireless communication is proposed. The antenna structure can be divided into six layers from top to bottom, including radiating layer, aperture layer, cavity layer, aperture layer, feeding layer and monopulse comparator. The upper radiating layer allows two transmission modes of the transverse electric (TE) wave and the transverse magnetic (TM) wave to pass through. The 90° phase difference can be obtained by adjusting the horizontal and vertical angles of the horn radiator, which realises the CP radiation pattern. Besides, the 0° or180° phase difference produced by the monopulse comparator enables the antenna to obtain a monopulse radiation mode. In order to obtain the low sidelobe characteristics, the coupling parameters of the coupling layer are weighted by the Taylor distribution. The overall size of the antenna is 194 × 25 × 31 mm3. The slot waveguide antenna is fabricated and measured to validate the proposed design. The measured results show that the monopulse system can achieve an impedance bandwidth of 3.7% (34.5–35.8 GHz) in the Ka‐band at the centre frequency of 35 GHz. The sum‐pattern maximum gain and radiation efficiency are 23.3 dBic and 75% at 35 GHz, and the gain of the whole bandwidth is >20 dBic. The axial ratio and the sidelobe level is less than 1.2 and −28 dB, respectively. The difference‐pattern amplitude imbalance is <0.2 dB and the null‐depth lower than −30 dB. Also, the isolation is better than 30 dB. Besides, the pure metal structure of waveguide has incomparable advantages in a harsh environment. [ABSTRACT FROM AUTHOR]

This study presents a single‐layer via‐less antenna array operating in circular polarisation for wide‐band operation in C‐band. The antenna comprises 2×2 disc based elements arranged in a sequential rotation architecture. Each element is tuned to exhibit multiple resonances with good circular polarisation performance over a broadband of frequencies. A proper feeding network is then designed so that the resulting array is capable of a wide‐band operation and enhanced gain, equalising the frequency response of the set of elements. Simulations are validated by fabricating and measuring a prototype realised on a commercial FR408 dielectric substrate. Notwithstanding a dimension of only 7×7cm2, that is only 1.66λ02 at centre frequency, measured performance of the proposed array can be summarised in a gain better than 7 dB over an operation bandwidth of 24.45%, which is an unmatched result, given the via‐less single‐layer technology and the specific available area. [ABSTRACT FROM AUTHOR]

The authors have proposed a dual‐band reconfigurable Fabry–Pérot (F‐P) cavity antenna with high gain and meanwhile small radar cross‐sections (RCSs) in wideband. Different from the traditional F‐P antennas, they used a dynamic metasurface reflective plane (DMRP) as the lower superstrate to realise reconfigurable functions and a digital coding metasurface as the upper superstrate to achieve wideband RCS reduction. To investigate the dual‐band reconfigurability, a wideband rectangular waveguide is used to feed the F‐P antenna. By varying the bias voltage applied to varactors embedded in the elements of DMRP, the reflection phase of DMRP is changed and the two operating frequencies can be tuned electronically. To realise RCS reduction, they adopted a meticulous arrangement of the coding elements on partially reflecting surface. The designed metasurface‐assisted F‐P antenna has good radiation performance with high gain, high aperture efficiency, and high radiation efficiency. In the experiments, a prototype was fabricated via printed circuit board technology, and measured results agree well with numerical simulations. The measured peak gain reaches 17.52 dBi and the maximum aperture efficiency is 56.97%. The two reconfigurable bandwidths cover 5.10–5.40 and 6.60–6.93 GHz, respectively; and 7 dB RCS reduction is achieved from 9.40 to 13.7 GHz for arbitrary polarisation [ABSTRACT FROM AUTHOR]

Although the ability of metasurfaces to control electromagnetic wavefronts has made it possible to design ultrathin carpet cloaks, the narrow operation bandwidth limits the performance of these cloaks. Here, the authors propose a new method to enhance operating bandwidth of metasurface‐based carpet cloaks. The proposed cloak consists of super‐cells providing appropriate phase shift to incident wave over a wide and continuous range of frequencies. Using the proposed method, a polarisation‐independent wide‐band single‐layer carpet cloak is designed and fabricated. The performance of the proposed technique is verified using both numerical and experimental data. Experimental results show that the cloak operates well at all frequencies in the range of 9–10 GHz. The proposed method can be used for designing single‐layer wide‐band metasurface‐based cloaks and illusion coatings at different frequency regimes. [ABSTRACT FROM AUTHOR]

A two‐port planar dual circularly polarised microstrip patch antenna is presented. The designed antenna has two groups of patches, each for transmission and reception. In one such group, only the central patch with truncated opposite corners is probe‐fed whereas the surrounding patches act as parasitic patches for bandwidth and gain enhancement. A defected ground structure (DGS) consisting 4 units of complementary square spiral resonators is used to enhance the port‐to‐port isolation as well as the axial ratio (AR) bandwidth. Based on the measured data of the fabricated prototype, the antenna is seen to have an impedance bandwidth of 900 MHz with the centre frequency of f0=6.40GHz. Moreover, the AR bandwidth is measured to be 600 MHz at fAR=6.36GHz, whereas the peak gain within this band is found to be ranging from 6.8 to 7.9 dBic. It is also noted that the AR bandwidth lies entirely within the impedance bandwidth and the cross‐polarisation discrimination is 20 dB in the boresight direction. [ABSTRACT FROM AUTHOR]

An innovative design of a right hand circularly polarised (RHCP) antenna at two different resonant frequencies that is GPS (global positioning system) L2 and L5 has been proposed in this study. The proposed design comprised the concept of slotted radiator excited with a coaxial probe. Two asymmetric spiral slots were incorporated in a rectangular radiator to realise size miniaturisation, the axial ratio bandwidth and beamwidth at L2 (1.22760 GHz) and L5 (1.17645 GHz) frequencies of GPS applications. The proposed design has accomplished an excellent axial ratio bandwidth and beamwidth at both GPS L2 and L5 bands. The size of the designed antenna has been 59.64×59.64×1.6mm3, which makes it attractive for the consumer market. Measured and simulated results achieved that the antenna conquered RHCP radiation at two separate operating bands, i.e. GPS L2 and L5. [ABSTRACT FROM AUTHOR]

An ultra‐wideband phased array antenna using interconnected elements arranged in triangular lattices is investigated. The basic unit cell of the array is a dual orthogonal crossed ring structure. Each element is interconnected to its neighbour using capacitive loading. The ring structure on a planar surface produces broad frequency bandwidth with wide scan angles. Unlike other three‐dimensional elements such as Vivaldi antennas, the interconnected crossed ring elements can be readily configured on a triangular grid. As is well known from narrow band arrays, a triangular grid allows reduction in the total number of elements needed for a given performance compared to a square grid. The array presented here applies the triangular grid to a broadband planar structure to reduce the total number of elements required by 13% while the electromagnetic behaviour of the array is essentially maintained. An array prototype of the design has been manufactured and tested. The performance is compared to the associated array with a regular square lattice. The proposed triangular grid structure is shown to be an effective solution for applications where a minimum number of elements is required for large‐scale broadband dual‐polarised antenna arrays. [ABSTRACT FROM AUTHOR]

In this study, a multi‐polarised two‐dimensional (2D) planar array of sparsely located vector antennas (VAs) is designed for the block sparse representation (SR)‐based 2D direction finding and polarisation parameter estimation of wideband signals. In order to alleviate the inter‐VA mutual coupling effect, the minimum inter‐VA spacing of the 2D sparse array is constrained to be no less than one wavelength that corresponds to the highest signal frequency. To reduce the computational complexity of parameter estimation, the 2D block SR model for the 2D difference coarray output at a certain frequency bin is established, under which the two direction cosine terms for 2D direction‐of‐arrival (DOA) estimation are decoupled with the polarimetric terms. This enables separated but simultaneous 2D direction finding and polarisation parameter estimation with the newly developed joint 2D block orthogonal matching pursuit (Joint‐2D‐BOMP) subband fused sparse recovery algorithm. Moreover, with the use of two spatial only (polarisation independent) over‐complete dictionaries, the representation dimension of the new 2D block SR model is greatly reduced as compared with the traditional space‐polarisation joint SR model. The efficacy of the presented VA array geometry and the associated parameter estimation method is validated by computer simulations. [ABSTRACT FROM AUTHOR]

This study presents a circularly polarised (CP) antenna with a wideband characteristic, which is caused by the interelement mutual coupling effect. The proposed antenna consists of a dipole array with four elements in centre symmetry and a wideband feed network. In order to extend the lowest working frequency, a strong mutual coupling effect is introduced to the adjacent co‐polarisation elements. What's more, the introduced effects of capacitive coupling reactance counteract the effects of the element's inductively reactive ground plane. Then, a small, tightly coupled array is formed that possesses wide impedance bandwidth and orthogonal polarisation component. A wideband feed network, including Wilkinson power dividers, phase shifters, and impedance converters, is designed to provide amplitudes and phases excitation that circular polarisation antenna required. Finally, a prototype is fabricated and tested. Measured results show a VSWR<2 impedance bandwidth of 102.7% (2.09–6.5 GHz) and a 3‐dB axial ratio bandwidth of 94.2% (2.25–6.25 GHz). Besides, a relatively stable gain is realised across the operating band. [ABSTRACT FROM AUTHOR]

A polarisation reconfigurable fractal slot antenna with dual‐band performance is proposed in this study. The antenna consists of a Minkowski Island fractal inspired slot in the ground plane, which is excited by a microstrip line. The input match of the antenna is improved by placing two protruding horizontal stubs inside the two corners of the fractal slot. Four p‐i‐n diodes are placed within the grounded fractal structure to realise polarisation reconfigurability. Based on the switching states of the p‐i‐n didoes, the proposed antenna can produce right‐hand circular polarisation or left‐hand circular polarisation. A novel biasing network is used, which uses only two wires for polarisation switching. A prototype of the proposed antenna is fabricated and tested. When the antenna is configured to radiate circular polarisation, the measured reflection coefficient bandwidths (corresponding to |S11|≤−10 dB) for the two bands are 15.44 and 13.16% and the measured axial ratio bandwidths (corresponding to AR ≤3 dB) are 17.61 and 8.69%, respectively. [ABSTRACT FROM AUTHOR]

The effect of using a non‐uniform reactive impedance surface (RIS) on the circular polarisation performance of a planar antenna is investigated. It is shown that a very wide axial ratio (AR) bandwidth can be obtained, especially when the RIS is combined with parasitic strips. This result is only possible, thanks to the fact that the RIS is non‐uniform. The technique is demonstrated by designing, building, and measuring a prototype. The simulated impedance bandwidth S11≤−10dB is 43.6% (4.3–6.7GHz), and the simulated 3 dB AR bandwidth is 37.2% (4.6–6.7GHz). The gain variation over the 3 dB AR bandwidth is 3–5.9 dBi. The experimental results are in good agreement with the simulations, validating the new concept. [ABSTRACT FROM AUTHOR]

A novel ring slot substrate‐integrated waveguides (SIW) antenna is presented based on higher‐order cylindrical cavity mode. First, TM02 is used to realise a conical beam antenna. Electric field distribution on slot aperture generates four pairs of magnetic monopoles, each rotated 90° with respect to the centre of the cavity, resulting in a conical beam. By applying an offset to the feed point, the loading effect of slots generates a hybrid mode, which is a combination of TM31 and TM12. The hybrid mode aligns the magnetic monopoles; thus, a high‐gain antenna with broadside radiation can be realised. The measured results show a 10.5% impedance bandwidth, 11.5 dBi gain, and 90% radiation efficiency. The proposed antenna is low‐profile and compact with a planar structure that could be integrated with other planar circuits; therefore, it could have many practical applications in communication systems. [ABSTRACT FROM AUTHOR]

This study describes a light‐weight wideband spiral antenna that radiates a unidirectional beam. To realise a light‐weight antenna, a one‐layer thick high‐impedance surface reflector (HISR) for a reference spiral antenna is replaced by a two‐layer circular HISR (TL‐CirHISR). The TL‐CirHISR is made of fan‐shaped patches printed on a dielectric substrate. It is revealed that a voltage standing wave ratio (VSWR) of <2 and an axial ratio of <3 dB are obtained across a design frequency range of 3.2–10 GHz (a fractional bandwidth of ∼103%). A weight reduction of 50%, compared to the weight of the reference spiral antenna, is achieved. A prototype spiral antenna with the TL‐CirHISR is fabricated and measured to confirm the analysed antenna characteristics, with good agreement between analysed and measured results obtained. [ABSTRACT FROM AUTHOR]

A dielectric lens is proposed here to broaden the half-power beamwidth (HPBW) of conventional circularly polarised (CP) patch antenna. The lens printed by the 3D technique is constructed by a dielectric cylinder with a stacked cone-shaped cavity. To illustrate the working principle, the energy distribution of the electromagnetic wave refracted by the lens is analysed. Besides, the design procedures of the lens are introduced in detail. The applicability of lens is also discussed including the changing of permittivity and dimensions. For verification, prototypes of the designed CP antenna with the lens are fabricated and measured. The performances of the CP antenna without lens are also provided for comparison. The measurements show that by using the proposed lens, the HPBW of the CP patch antenna is extended effectively from 69° to 170° while maintaining a wide 3-dB axial ratio beamwidth of >200°. [ABSTRACT FROM AUTHOR]

This study reports on a highly miniaturised polarisation selective surface (PSS) for dual-band Wi-Fi and WLAN applications. The proposed unit cell consists of two independently tuneable square loops. The outer loop is split with a gap of 0.2 mm to introduce polarisation selectivity and miniaturisation for lower-frequency band of 2.5 GHz. The inner square loop is inductively loaded with arms to suppress 5.45 GHz frequency band. These configurations have resulted in a unit element size of $\lambda _{\circ }/14$λ∘/14 at 2.5 GHz, which is not presented before to the best of the authors' knowledge. A wide rejection bandwidth ($-10\,{\rm dB}$−10dB) of more than 600 and 1180 MHz is obtained around 2.5 and 5.45 GHz, respectively. Furthermore, the proposed PSS exhibits an excellent polarisation selective characteristic by generating two stopbands at 2.5 and 5.45 GHz when illuminated by horizontal (TM) incident waves, whereas vertically (TE) polarised incident waves result in the generation of passbands for these two frequencies. Numerical validation through equivalent circuit modelling of the proposed PSS has also been carried out. A finite prototype containing $31 \times 33$31×33 elements is fabricated and tested. The measured results demonstrated that the PSS has excellent potential for applications that employ polarisation separators and wave generators. [ABSTRACT FROM AUTHOR]

This study presents a broadband metasurface harvester with polarisation-insensitive and high harvesting efficiency. The proposed metasurface constitutive main cell consists of two intertwined modified inner and outer Jerusalem cells with two combined different resonance frequencies to obtain a broadband bandwidth. The parameters of the proposed cell are optimised to capture the energy of ambient electromagnetic waves with the least possible return loss and deliver it to the resistive loads through optimally positioned vias. The optimum load resistance value for the proposed harvester is $100\,\Omega $100Ω. The simulation results obtained from CST Microwave Studio solver show relative band width of $18\%$18% from $8.75$8.75 to 10.5 GHz for different polarisation angles under a normal incident plane wave. Finally, an array of $8\times 8$8×8 cells of the proposed harvester has been fabricated and its electromagnetic properties have been measured which show good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

A novel gain/bandwidth enhanced leaky‐wave microstrip line antenna with circular polarisation (CP) is proposed. Different from common leaky‐wave antennas with an open, short or resistive termination, this antenna consists of a leaky‐wave rampart‐line antenna terminated with a CP patch radiator. The energy from the feeding point is first radiated by the rampart‐line antenna, while the remaining part is radiated through the CP patch element. As a result, the size of the leaky‐wave part can be reduced. The resulting size of this antenna is only 1.6 × 1.6 λ2.4G (λ2.4G is free space wavelength at 2.4 GHz). Energy loss caused by the resistive termination is avoided, so that high efficiency is achieved – higher than 85% within the whole band. By introducing slight CP centre frequency difference between the patch and rampart antenna, two CP resonances were generated and the 3 dB axial ratio (AR) bandwidth is substantially broadened. Measured AR bandwidth is 9.9% (2.30–2.54 GHz). Its − 10 dB impedance bandwidth is 2.25 GHz to higher than 3 GHz, and peak gain is 13.2 dBic. The proposed antenna has a fully used radiation aperture, achieving a favourable performance, such as wide bandwidth, high gain, and a relatively stable (less tilted) boresight radiation. [ABSTRACT FROM AUTHOR]

Broadband polarisation reconfigurable antenna based on crossed dipole and parasitic elements is proposed in this study, which can switch among three polarisation modes, i.e. linear polarisation, left‐hand circular polarisation and right‐hand circular polarisation. The proposed antenna consists of two crossed dipoles fed by a 3/4 square ring, two microstrip feeding elements etched at the centre of the upper and lower sides of the dielectric substrate, and three sets of microstrip parasitic elements helping broaden the axial‐ratio (AR) bandwidth. Four PIN diodes are embedded between each crossed dipole and the microstrip feeding element, which enable the polarisation reconfigurability. The working principle of polarisation reconfigurability is analysed in detail. The measured results show that the proposed antenna has a −10 dB overlapped impedance bandwidth of 63.5% (2.04–3.94GHz) and the 3 dB overlapped AR bandwidth is about 54.5% (2.4–4.2GHz), resulting in a wide overall bandwidth of 48.6% (2.40–3.94GHz). Besides, the measured peak gain of this antenna reaches up to 8.5 dBi. The proposed antenna can be a good candidate for 2.45GHz WiFi, LTE 4G, and sub‐6GHz 5G applications. [ABSTRACT FROM AUTHOR]