In recent years, the microwave processes in artificial multiferroic media such as electromagnonic crystals have attracted increased research interest due to their potential applications for voltage-controlled spintronic devices. In contrast to the conventional magnonic crystals, the artificially created periodic structures are characterised by electrically and magnetically tunable band gaps in the wave spectrum where the propagation of the electromagnons is forbidden. In this study, an experimental realisation of an electromagnonic crystal based on a ferrite–ferroelectric–ferrite multilayer has been proposed. The authors have demonstrated for the first time a band-gap splitting, which arises from an interaction of three fundamental modes of two ferrite films separated by a ferroelectric layer. This splitting manifested itself as an additional stop-band appearance in the frequency response of the electromagnonic crystal. The obtained band structures are confirmed by numerical modelling using the coupled-mode approach and the transfer-matrix method. The authors expect that their results allow exploiting the electromagnonic crystal for enhanced logic control as well as for tunable microwave devices.

This work presents a new technique for the geometrical optics (GO) shaping of axisymmetric dual-reflector antennas. Both reflectors' generatrices are shaped by the continuous concatenation of conic sections, suited to provide simultaneous control of amplitude and phase of the aperture's GO field. With amplitude and phase control of the aperture field, the antenna designer has more options to achieve prescribed circularly symmetric radiation patterns. The GO formulation is derived for the well-known shaped Cassegrain configuration, but it can be easily adapted to other axisymmetric geometries. Illustrative GO designs are investigated and results validated by a full-wave analysis provided by the method of moments.

A chipless radio frequency identification (RFID) system based on multi-resonant-based chipless RFID tags and fractional Fourier transform (FrFT) was simulated. Each tag codes a 3-bit unique identification (ID) in the form of a spectral signature in the interrogation signal. The signal is then backscattered to the processing unit (PU) for ID decoding. The simulated system accounts for two tags, 1 m apart and with a line-of-sight between them and the PU. At the PU, the received signals from the tags at 4 and 5 m present a signal-to-noise ratio of 7.9 and 4.0 dB, respectively. The signals from both tags collide in the time and frequency domain. FrFT is used at the PU to retrieve the ID of each tag by transforming the combined received signal from the time-frequency domain to a fractional domain where each backscattered signal takes its most compact form. Using Hamming windowing in the fractional domain, each ID was successfully recovered. This work puts chipless RFID one step closer to become a reality and replacing the barcode in the labelling market.

A technique is proposed for the enhancement of gain and circularly polarised (CP) bandwidth of a singly-fed CP dielectric resonator (DR) antenna. The specific geometry of DR is used to generate the orthogonal modes required for obtaining the CP response. The incremental harmonics of the fundamental and third-order modes, and , are generated by stacking of the similar DR layer topped with metallic patch after an air gap. This enhances the gain and CP bandwidth of the antenna maintaining the generated orthogonal modes with the required phase difference. The antenna with single DR layer provides the CP bandwidth of 13.56% and gain 4.04 dBic. After stacking, the antenna provides the measured CP bandwidth of 24.75% and 7.32 dBic stable gain over the passband. In addition, the antenna provides 92.87% radiation efficiency in the passband.

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 λ_2.4G (λ_2.4G 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.

As the interference bandwidth increases, the impact of interference coupling path dispersion on the cancellation performance can no longer be ignored in open space. Especially for the radio frequency interference adaptive cancellation system (RFIACS), the impact will be more serious. In response to this problem, this study establishes the time-domain model of a wideband RFIACS considering interference coupling path dispersion characteristics, and analyses the stability, convergence speed, interference cancellation ratio (ICR), and cancellation bandwidth of RFIACS considering dispersion characteristics. And the authors define the speed factor to characterise the convergence speed. The analysis shows that the dispersion of the interference coupling path will not affect the stability of the system, but will reduce the convergence speed and ICR. The larger the interference coupling path dispersion, the lower the convergence speed, and the larger the cancellation bandwidth, the lower the ICR. The experimental results verify the theoretical analysis.

This study addresses an analogue method for mitigating the non-linearities introduced by discrete supply modulation of a high-efficiency power amplifier (PA). A 10 W two-stage X-band gallium–nitride monolithic microwave integrated circuit ( PA with a peak power-added efficiency of 55%, is tested with drain supply modulation from 10 to 20 V with an increase in efficiency and substantial degradation in linearity. In this work, the authors characterise the two-stage PA dynamically to develop shaping functions for both gate bias voltages. They demonstrate that gate modulation can improve back-off gain and linearity, specifically when gate biases of the two stages of a PA are independently modulated. Simultaneous gate and drain modulation results in 15 percentage point improvement in efficiency over a static supply, and a consistent improvement in noise power ratio over a static supply, for a 20 MHz noise-like signal. Results with a 20 MHz long-term evolution signal show comparable improvement in efficiency while maintaining adjacent channel power ratio near the level of the PA with a static supply.

This study presents a wideband crossover developed using substrate integrated coaxial line (SICL) technology. The proposed SICL-based crossover isolates the two physically overlapping channels by routing the signal in a middle conductor of SICL through the transmission line created in the top and bottom ground plane using a metalised blind via. An equivalent model is proposed to study the role of substrate height in the proposed crossover. The design methodology is affirmed by fabricating and testing the experimental prototype. The measured results show isolation between channels are more than 19 dB with better than 18 dB return loss and less than 1.2 dB insertion loss from 0.2 to 20 GHz. Owing to the non-dispersive nature of SICL line and simplistic design technique with minimal discontinuities the designed crossover demonstrates low peak-to-peak group delay variation, less than 0.04 ns over the entire bandwidth. The proposed crossover due to its symmetric design provides low path difference of less than 2.45 up to 20 GHz ( up to 10 GHz) without any additional phase compensation technique. Utilization of electromagnetically robust self-packaged components designed in SICL technology provides superior front-end communication system within a small footprint.

Moving toward commercialisation of chipless radio-frequency identification (RFID) systems, there is a significant challenge for the detection of chipless tag in a practical application, in which the conventional calibration techniques such as background subtraction are insufficient or even impractical. In this study, first, a processing algorithm for an inverse problem based on the range estimation is introduced. In an inverse problem, the tag ID and its distance to the reader are unknown. Employing the proposed algorithm, provided the specification of the reader antenna is known, the desired component of the received signal corresponding to the tag ID can be extracted without the requirement of background calibration. Then, a post-processing algorithm is proposed for the extraction of the tag ID, which provides a sustained detection outcome at an arbitrary distance. The proposed algorithms are verified with the help of a few datasets acquired from the simulation environment as well as measurement setups. A typical backscattering chipless RFID tag with six resonances is examined. The distance between the tag and the reader antenna is estimated, and the binary tag ID extracted successfully.

This study proposes a design of a double-sided printed dipole (DSPD) antenna array with a low first sidelobe level (FSLL) for interference suppression. The proposed array consists of ten DSPD antennas based on the Rogers RO4003C substrate (ɛ_r  = 3.55). The FSLL has been compressed by imposing a single null at the centre of the first sidelobe. The excitation power distribution of the array has been calculated by using the bat algorithm with the amplitude-only control technique and has been implemented by a series-fed network. A back reflector, which is based on an FR4 substrate (ɛ_r  = 4.4), has been used to improve the maximum gain. The simulation results show that the FSLL can be reduced with a null deep level (NDL) of −40 dB in the E-plane at the frequency of 3.5 GHz, while the maximum gain of the array is around 17.7 dBi, and the bandwidth is 600 MHz (3.3–3.9 GHz) with −10 dB of S ₁₁. A prototype of the proposed DSPD antenna array has been fabricated and measured. A good agreement can be achieved between simulation and measurement results.

This study explains a novel wideband curvilinear Sierpinski fractal geometry (CSFG) based cylindrical dielectric resonator antenna. CSFG provides wider bandwidth by the combination of two important concepts: (i) reduction in volume to the surface area of the complete radiating structure, which in turn reduces the Q-factor; (ii) generation of two radiating modes inside the radiating structure HEM_11δ and TM_01δ. The prototype of the proposed antenna is fabricated for verifying the simulated results. Measured reflection coefficient (|S ₁₁|) shows that the proposed antenna structure operates over the frequency range 2.2–3.5 GHz with the fractional bandwidth of 45.61%. Diversified radiation pattern, i.e. monopole (due to TM_01δ mode) and broadside (due to HEM_11δ mode) is also an important feature of the proposed antenna structure. The antenna design is relevant for WLAN (2.5 GHz) and WiMAX (3.3 GHz) applications.

In this study, a novel broadband rectenna system, capable of extracting energy from multiple RF sources is presented. The proposed topology employs a novel rectifying circuit comprising a two-port differential rectifier integrated with the hybrid coupler on a single board, which is the first structure of its kind possessing higher reliability. During measurement, the maximum efficiency of the proposed rectifying circuit is found to be at 4 dBm with the maximum DC voltage of 3.6 V. The proposed broadband RF energy harvesting circuit, comprising the newly designed rectifying circuit integrated with a broadband high gain Yagi antenna, can operate in the frequency range starting from 1.55 to 2.6 GHz. The broadband operation of the proposed rectenna is validated by performing measurement at three frequency points 1.81, 2.08 and 2.45 GHz using both single tone and two-tone methods in the anechoic chamber as well as in the lab environment. The proposed broadband rectenna configuration can potentially be used for extracting the RF energy simultaneously from multiple RF sources, while delivering the maximum power to a standard load.

This study introduces modelling of multi-adaptive neuro-fuzzy inference system (MANFIS) for predicting the bandwidth and notch frequencies of slotted ultra-wideband (UWB) antennas. Rectangular-shaped printed monopole antennas embedded with U-shaped slots are designed to realise triple band-notch characteristics. A MANFIS model is then developed to predict five output parameters (two cut-off frequency points and three notched frequency points) considering 15 geometrical variables of the designed antennas as the inputs of MANFIS model. Extensive simulation has been performed using HFSS software to generate training and testing data patterns. Two optimisation algorithms, genetic algorithm (GA) and particle swarm optimisation (PSO), are implemented to optimally determine the appropriate values of the fuzzy inference system parameters. For GA-optimised MANFIS model, the percentage error is observed between 1 and 2%, whereas, in PSO-trained MANFIS model, it is observed <1%. The comparative analysis establishes that the PSO-trained MANFIS model precisely predicts the antenna performances. For validating the proposed modelling technique, an optimised configuration of the slotted UWB antenna prototype has been fabricated and characterised.

In this study, the ultra-high-frequency (UHF) antenna for partial discharge (PD) detection is optimised to simultaneously satisfy the requirements of low return loss and high fidelity factor (FF) in the frequency band of interest by using the modified non-dominated sorting genetic algorithm II (MNSGA-II). Based on the labour division strategy, the MNSGA-II adopts an adaptive crossover and mutation possibilities instead of the fixed ones, resulting in the significant improvement of convergence rate and exploration ability. One of the Pareto-optimal solutions is presented as the authors’ proposed UHF antenna, whose performance is compared with those of both the antenna optimised by genetic algorithm and the existing wideband antennas. The experimental results show that the proposed antenna with a compact size of 0.201 λ _L × 0.198 λ _L realises the reflection coefficient less than −10 dB from 490 MHz to 1.52 GHz, and its FFs in the face-to-face and side-by-side scenarios are 0.897 and 0.845, respectively. Furthermore, the simulation results reveal that the high FF of antenna greatly increases the accuracy of PD source localisation. It indicates that the MNSGA-II provides an excellent solution to the multiobjective optimisation problems in antenna design.

This study shows the potential of additive manufacturing for the fabrication of 3D Phoenix phase-shifting cell. With traditional microstrip printing technology, the cell has many advantages. Here, the authors demonstrate that the 3D printed version of the cell exhibits very good intrinsic performances in the 17–21 GHz frequency band. A deep insight into the operation mode of the cell is drawn in order to have a better understanding of its behaviour. Different prototypes are fabricated and measured to validate experimentally the numerical results.

In this work, a compact antenna employing the substrate integrated waveguide (SIW) technology is investigated to achieve the characteristics of wideband and high gain. A pair of novel elliptical patches, which operate as an electric dipole, are loaded on the upper surface of the antenna. Two bow-tie-shaped slots are etched in parallel on the upper surface of SIW to obtain the features of magneto dipole and wideband. Combined with the low profile character of the SIW, the low cost of printed circuit board technology and the broadband characteristic of magneto-electric (ME) dipole, a 1 × 8 SIW ME-dipole antenna array is proposed and fabricated. The experimental result of the proposed prototype shows that the 10 dB impedance bandwidth is 42.3% from 19.4 to 29.8 GHz, which is basically consistent with the simulated result. Moreover, the antenna gain up to 14.6 dBi and the radiation efficiency higher than 82.6% are also obtained during the experiment. In the whole resonance band, excellent directional radiation, cross-polarisation level <−25 dB and gain fluctuation <2.7 dB all suggest that the array can be applied to a fifth-generation wireless network.

In this work, an ultra-wideband gradient metasurface (GM) is designed by using Pancharatnam–Berry (PB) phase. In the design process, a circular polarisation (CP)-maintaining metasurface (CMM) is proposed at first, which can realise ultra-wideband CP-maintaining reflection in the frequency band of 7.7–19.9 GHz, moreover, PB phase will be generated in its co-polarised reflection coefficient under CP incidence by rotating the anisotropic resonators in its unit cells. Thus, based on the CMM, an ultra-wideband GM is designed by using PB phase. Both the simulation and experiment show that the designed GM can realise ultra-wideband anomalous reflection under arbitrary polarised incidence, the reflected wave under CP incidence will be deflected to an anomalous direction and even be converted to a surface wave; but under linearly polarised and elliptically polarised incidences, the reflected wave will be separated into two beams. In addition, to design more anomalous reflection metasurfaces, the generation principle of PB phase, together with the root cause of the CP-maintaining reflection of the proposed CMM, has been analysed in detail in the designing process.

This study reports, for the first time, the use of coupled-line-based impedance matching in wireless power transfer (WPT) system. The transmitter and receiver of the WPT system are realised by microstrip feed line and symmetric coupled line at the top plane. The ground plane is realised with triangular-shaped defect along with the excitation slot mounted by an external capacitor. The defect in the ground plane and the external capacitor regulate the resonant frequency and also enable miniaturisation of the WPT system. The design is augmented with a systematic analytical approach for impedance matching and a simplified design procedure for the WPT system. A novel equivalent circuit model consisting of parallel LC network and coupled lines is also developed for the evaluation of the proposed WPT system design technique. A prototype of the system operating at 300 MHz developed on Rogers RO4350B substrate achieves a peak efficiency of 80% at a transmission distance of 17 mm. An excellent agreement between the measured and the electromagnetic simulated results is a testament of the robustness of the proposed design technique. Furthermore, evaluation of the commonly used WPT-related figure of merit shows significant enhancement when compared to the existing state of the art.

In this study, the authors propose an innovative solution based on mantle cloaking method to restore the performance of an implantable antenna, which is degraded due to the scattering from an adjacent metallic body. In an implantable device, the metallic body is generally used as a house for electronic circuitry. Initially, they investigate the deteriorating effects of metallic body on the antenna input impedance and radiation characteristics. Finally, by covering the metallic body with the designed metasurface, most of the antenna parameters are successfully retrieved. The proposed model is fabricated and measured with the in vitro test by immersing the antenna inside a muscle emulating gel, as well as, inside the minced pork.

In this study, a new type of horizontal radiation blade structure is proposed and applied to the very high frequency (VHF) broadband whip antenna. The influence of the radius, length, number of branches of horizontal radiation blade and its distribution on the whip body on the electrical performance of the whip antenna is analysed separately to design a more suitable structure, and then an algorithm optimization of single loading and broadband matching network is carried out for further impedance matching. The simulation and measured results both show that compared with the existing broadband whip antenna, the gain and efficiency of the proposed antenna are significantly improved while maintaining a good voltage standing wave ratio (VSWR) over the frequency band of 30–300 MHz, all the VSWR are <3 with an average value of 2.0; all the maximum gain are >−3.5 dB, with an average value of 2.2 dB; and all the efficiency are >15%, with an average value of 47.7%; the pattern deviation in higher frequency is also suppressed to some extent. The proposed antenna has small size, wider bandwidth and higher radiation performance, which is suitable for vehicle-borne and ship-borne VHF communication.

A super compact parasitic patch loaded patch antenna with enhanced gain and super wide band is proposed in this study for 5G millimetre-wave (mm-wave) applications. The proposed antenna has hybrid geometry and is constructed using circular and two rectangular driven patches with two semi-circular parasitic patches fed by stepped impedance microstrip line. The two rectangular stubs are incorporated on driven patch to improve the voltage standing wave ratio (VSWR) bandwidth. The two semi-circular parasitic patches are added on the fundamental radiator (driven/main patch) to further enhance the bandwidth to cover the entire K_a-band spectrum for 5G mm-wave requirements and covers 24–40 GHz frequency spectrum with VSWR ≤2. This designed radiator is feasible to be placed inside the multilayered housing systems or can be integrated along with the electronic components existing on the printed circuit board. Furthermore, a four-element modified corporate feed array configuration is constructed and their enhanced gain performances are compared with proposed radiator (single element). Both the prototypes are fabricated and experimentally validated for impedance and radiation characteristics and it is observed that, the simulated and measured responses are in good arrangement. The presented radiating element finds its applications in future 5G mm-wave, 5G base station controlling networks and 5G wideband code division multiple access.

A novel microstrip lowpass filter design using rectangular split-ring resonators with dual splits are designed, analysed, and fabricated with exceptional performance such as ultra-wide stopband and sharp roll-off rate along with its compactness. The symmetrical suppressing cells are also employed to reject higher-order harmonics from the stopband without affecting selectivity. The expression for transmission zero of dual split resonator-1 is extracted from the equivalent circuit analysis and observed the significance of coupling. A sharp roll-off performance of 224 dB/GHz and relative stopband width of 161% are achieved with a cut-off frequency of 2.9 GHz.

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% (2.04–3.94 GHz) and the 3 dB overlapped AR bandwidth is about 54.5% (2.4–4.2 GHz), resulting in a wide overall bandwidth of 48.6% (2.40–3.94 GHz). Besides, the measured peak gain of this antenna reaches up to 8.5 dBi. The proposed antenna can be a good candidate for 2.45 GHz WiFi, LTE 4G, and sub-6 GHz 5G applications.

An ultra-wideband (UWB) array is presented for UHF-S band (0.19–2.3 GHz) communications with an emphasis on dual-linear polarisation and wide-angle scanning. The array achieves 12:1 impedance bandwidth for a voltage standing wave ratio (VSWR) <3 at broadside with low-angle scanning off broadside to 0°, 45°, 60° in the E-plane (VSWR < 3, 4, 3.1) and 0°, 45°, 60° (VSWR < 3, 3.8, 5.5) in the H-plane. A 7 × 11 prototype was fabricated and tested for verification. In addition, finite effects with respect to mounting UWB arrays in airborne platforms are discussed. Specifically, the effect of radomes, perfect electric conductor shielding walls and resistive walls on the gain of the designed tightly coupled dipole antenna was studied, showing that losses can approach 2 dB.