An innovative aperiodic phased array antenna architecture with quantised excitation for space-borne synthetic aperture radar (SAR) is presented. Compared to traditional periodic arrays, the proposed array antenna enjoys two major advantages including (i) much higher overall power efficiency and (ii) phase-only control for both transmitting (TX) and receiving (RX) patterns to fit different space SAR beam shaping and steering requirements. The unprecedented studies on the quasi-optimum TX and RX pattern strategies for space SAR are carried out and this strategy is utilised in the design of the proposed aperiodic phased array. Performance of the proposed array when being applied to space SAR are evaluated. Moreover, the authors obtained positive results which endorse the design.

A slot array in substrate-integrated waveguide (SIW) technology fed by a microstrip Rotman lens is proposed. This compact multibeam antenna is designed in two layers using a novel transition based on double-stepped coupling slots on the broad wall of SIWs. Compared with a rectangular transverse coupling slot, this transition is broadband and its coupling power can be controlled for low-sidelobe applications. The radiating part is a 10 × 10 slot array and the beam-forming network can generate seven beams with good coverage from −30° to 30° in the azimuthal plane. To validate the proposed concept, an antenna prototype is implemented at 10 GHz. The frequency response and measured radiation patterns are in good agreement with simulated results provided by full wave simulation software. Experimental results show that the sidelobe level is lower than −21 dB for the central beam in both H and E planes and better than −18 dB for the edge beams.

The study deals with the application of low-temperature co-fired ceramic (LTCC) technology for design of a higher-order mode dielectric resonator antenna element operating at centre frequency 25.7 GHz. The LTCC material that the authors use provides very low dielectric losses and enables us to design an antenna element with very high radiation efficiency. The authors follow by examining the mutual coupling between two resonators and the authors propose a small (1 × 4) one-dimensional antenna array composed of such elements. In order to minimise the dimensions of the ground plane and to place the connector at a convenient location, the authors design a parallel feed network in substrate integrated waveguide technology, thus reducing the radiation losses of the feeding structure. The experiments verify the four-element antenna array concept with maximum measured gain of 16.3 dBi.

A dual-stub co-planar Vivaldi antenna with a parasitic element is presented. The dual stub is coupled between the parasitic element and two tapered slots. The parasitic element shape and size is optimised. The use of slits on the outer edge of the ground plane is shown to provide control of beamwidth and maximum gain. A bandpass filter is used for performance control and sub-harmonic suppression.

In this study, a millimetre-wave (MMW) antenna is presented for the fifth-generation (5G) wireless multiple-input multiple-output (MIMO) applications, in order to offer numerous advantages including compactness, planar geometry, high bandwidth, and high gain performance. The concept of defected ground structures has been deployed for the first time in MIMO antenna design at MMW spectrum to fulfil 5G requirements of high bandwidth with compactness and low design complexity. The top surface of antenna comprises of a coplanar waveguide-fed T-shaped radiating patch element, while the bottom part is designed to constitute a partial ground loaded with two iterations of symmetrical split-ring slots at an optimised distance. Experimental results depict a wide bandwidth of 25.1–37.5 GHz, as well as a peak gain of 10.6 dBi at 36 GHz. Moreover, numerically evaluated efficiency of >80% is observed over the entire intended bandwidth of operation. For the demonstration, four-element MIMO antenna array of the proposed antenna element is also fabricated and tested, in order to validate high isolation between the adjacent elements, which makes the proposed antenna a potential candidate to be integrated in cellular phones and base stations for 5G MIMO systems and services.

This paper presents an improvement of small RFID tags detection in HF near field, whatever their lateral and angular misalignments, using a complementary sub-coils reader antenna, enhanced by coplanar weakly-coupled resonators, and conformed on a 3D tube. The key ideas of detection improvement are: (i) modification of B-field vector distribution with the complementary coils above the common edge of consecutive loops; (ii) increase of B-field vector diversity and magnitude distribution by a 3D structure conformed on the tube, by realising 2 pairs of Identical Coaxial Loops (ICLs) with face-to-face sub-coils in forward current, and (iii) enhancement of B-field magnitude distribution by resonators included in the complementary sub-coils. Numerical simulations are carried out using High Frequency Structure Simulator (HFSS). The studied figure-of-merit is the mutual inductance between the tag and the reader coil. Results are reported for the 4 planar complementary sub-coils, the previous structure conformed on the tube and for the structure in which RCL resonators are added in the 3 planar complementary sub-coils. Experimental detection range measurements of each fabricated structure drives to the enhancement of the 3D complementary 4 × 3 sub-coils structure with weakly-coupled RLC resonators in each-sub-coil in terms of read-out distance and detection surface area.

In this study, a reader antenna including resonators is proposed to improve detection of a small moving tag in the case of tracking a radiofrequency identification (RFID) system. The near-field RFID technology is based on load modulation, the input impedance on the reader coil and the mutual inductance between the reader and tag coils are the main parameters for performing detection. They are calculated from the impedance matrix parameters. The added resonators change all the parameters of the impedance matrix consequently the input impedance and mutual inductance are also changed. In this study, analytical formulation defining the equivalent impedance matrix parameters is developed. These formulae are used to evaluate the performance of the proposed design according to the tag misalignment (lateral and angular). From the calculation and simulation results, a frequency shift in the equivalent input impedance is found. To avoid this problem, optimising the positioning of the resonators on the reader coil is performed. This study is confirmed by measures of RFID detection for a reader prototype (with and without resonators) and a small commercial tag. Both the surface and volume of detection of the small moving tag (lateral and angular misalignment) are improved by the principle of added resonators.

A coupling frame (CF)-based high-frequency radio-frequency identification (HF RFID) card is composed of a metallic CF with a slot and a module (contains a small coil and an integrated circuit). This provides higher coupling and better performance in comparison to the standalone module. Such design eliminates the need for a mechanical connection between the module and card body (metal frame) which leads to reduced manufacturing costs. Further, it enhances the card's robustness against mechanical stress. The authors explain the operation of such a design from first principles and highlight the effect of the slot on the performance. In addition, a circuit model for the card is derived. Furthermore, they propose an enhancement to the card design which improves the card's performance with two variations either in terms of better transferred voltage (up to three times higher) or more bandwidth (up to double). The enhancement is shown by HFSS simulations, circuit simulations and corresponding measurements including the HF RFID integrated circuit. Finally, a double CF-based design is proposed and analysed which simultaneously achieves increased bandwidth and higher transferred voltage. The results are compared to those of conventional HF RFID cards with galvanic coupling to the integrated circuit.

An explicit analysis of the retrodirective mechanism of a flattened dihedral using periodic arrays is proposed. Once flattened, a corner dihedral requires a phasing mechanism to restore its retrodirective behaviour. This can be achieved by equipping each of the panels with passive phase-shifting cells that obey a global retrodirective phase law. The challenge is to have a trade-off between two steering mechanisms on each side such that this global phase law is achieved. In this work, an analytical study of the reflection phenomenon between the two panels is presented and sufficient information are provided to predict the retrodirective performance affected by the dihedral geometrical configuration itself. The analytical formulation of the global phase law is thus defined along with other complementary formulations to provide a better understanding of the reflection phenomenon involved. Based on these analysis and comprehension, guidelines are suggested in terms of the cell design and the dihedral geometrical configuration so that to efficiently engineer the retrodirective profile of the dihedral. A simple method utilizing these guidelines is proposed to enhance the flattened dihedral performances. And an experimental validation of this design is finally proposed at 24 GHz.

This study presents a low-cost, compact and lightweight radio frequency (RF) switching system for wearable head imaging applications. The proposed switching system is made from commercial off-the-shelf components. The switching system provides a wideband performance which covers operating frequency band from DC to 4 GHz. A low-power microcontroller is integrated with two RF switches as a control system. An array of 12 wideband monopole antennas were connected to the proposed switching circuit and its performance was evaluated using an artificial human head phantom. To verify the performance of the system, a haemorrhagic stroke was mimicked by placing a spherical target of 30 mm in diameter inside the fabricated head phantom. Two data acquisition methods were applied using the switching system. In the first method, the reflection coefficients of the antennas were collected for healthy and unhealthy brain injury cases. For the second method, the transmission coefficients of the antennas were collected by utilising four antennas in the array as transmitting antennas while the rest of the antennas act as receiving antennas. The authors demonstrate that the proposed compact switching system could be used for future real-time wearable detection systems embedded in various headgear products.

An experimental verification of a fast and accurate technique, which allows the evaluation of the antenna radiation pattern from a non-redundant, i.e. minimum, number of near-field (NF) measurements acquired via a bi-polar scan, is provided in this study. This probe compensated NF-to-far-field (NFTFF) transformation exploits a non-redundant sampling representation of the voltage acquired by the probe, achieved by shaping the antenna with a double bowl, a very flexible model particularly tailored to antennas characterised by a quasi-planar geometry. The input NF data necessary for executing the standard plane-rectangular NFTFF transformation are efficiently recovered from the acquired non-redundant bi-polar ones by applying a two-dimensional optimal sampling interpolation formula, so that a remarkable measurement time saving is attained. Some results of laboratory proofs performed at the Antenna Characterization Lab of the University of Salerno are reported to demonstrate the accuracy and the practical effectiveness of the presented NFTFF transformation technique.

A multi-polarised quad-band planar circular disc monopole antenna consisting of a parasitic double T-stub and parasitic long and short inverted L-stubs is presented. By loading parasitic multistubs along the y-axis behind a circular patch, the antenna can yield four resonance modes at 2.5, 4.5, 5.7, and 7.7 GHz frequencies while keeping the size of 30  ×  40 mm². The proposed antenna has been fabricated and experimentally studied. The measured impedance bandwidths of 290 MHz (2.36–2.65 GHz), 540 MHz (4.28–4.82 GHz), 530 MHz (5.47–6.0 GHz), and 780 MHz (7.28–8.06 GHz), for Bluetooth, 2.4/5.8 GHz wireless local area network, 2.5/5.5 GHz worldwide interoperability for microwave access, 5.9 GHz intelligent transportation systems (ITS), downlink of Indian National Satellite System and X-band satellite applications. The 3 dB axial ratio bandwidth is 280 MHz (5.79–6.07 GHz) for the 5.9 GHz ITS band. The antenna E-field radiation has y-directed (vertical linear) polarisation at first, second, third resonance bands and slant + 45° linear polarisation at the fourth resonance band. At the ITS band, the E-field radiation has right-handed circular polarisation. In addition, the design procedure, electrical model and effects of parasitic stub dimensions on the antenna characteristics are discussed.

In this study, an on-chip antenna with miniaturised artificial magnetic conductor (AMC) structure loading is designed and fabricated in the 65 nm complementary metal oxide semiconductor process at 235 GHz. The proposed on-chip antenna consists of a double-layer dipole and miniaturised AMC with wide bandwidth and low-backward radiation. A quarter square loop structure for the miniaturised AMC is designed and analysed by the current and electric field distributions. The simulation results show that the miniaturised AMC has a similar resonant frequency and lower reflection loss compared with the original one. The die area of the proposed antenna is . The measurement of the −10 dB impedance bandwidth is 81 GHz (200–281 GHz). The gain of the antenna is up to 0 dBi at 235 GHz. By loading the miniaturised AMC, the on-chip antenna can obtain higher gain, wider bandwidth than that loading the original one. Good agreement can be well observed between the simulated and measured results.

In this research article, a dielectric resonator-based multiple input multiple output (MIMO) antenna system is presented with dual band characteristics. The proposed MIMO antenna includes two symmetrical hybrid radiators. Each hybrid radiator consists of a modified annular ring printed line along with a cylindrical dielectric resonator antenna (CDRA). A modified annular ring printed line acts as a magnetic dipole and creates two different radiating modes (HEM_11δ and TE_01δ ) in the dielectric resonator. The approach of the hybrid antenna (combination of the modified annular ring printed line and CDRA) is taken into account for achieving dual band characteristics. Orthogonally placed antenna elements and a narrow slit in the ground plane are used to improve isolation (|S ₁₂| < −20 dB) in the entire operating frequency range. The antenna prototype is fabricated and measured for validating the simulated results. The proposed MIMO radiator is operating over two frequency bands, i.e. 1.75–2.4 and 3.5–5.5 GHz. Different MIMO diversity performance parameters (envelope correlation coefficient, diversity gain, mean effective gain, total active reflection coefficient, and channel capacity loss) are also inspected and found within acceptable limits.

In this study, a three-dimensional (3D) time-varying dusty plasma iterative finite-difference time-domain (FDTD) algorithm is deduced by combining the relative permittivity of fully ionised dusty plasma and the shift-operator FDTD method. Then, a 3D time-varying dusty plasma model is established. The scattering characteristics of electromagnetic (EM) waves are analysed by calculating the backward radar cross-sections (RCSs) of different parameters in time-varying dusty plasma. The results show that the RCS will increase when the dust particles are considered in plasma. The values of RCS increase with the dust radius dust concentration relaxation time of charge and electron density increasing. In dusty plasma, the electron temperature has a different effect on the incident wave frequency bands. Finally, the effects of dust to electron density ratio on RCS are analysed and as the increase of the incident frequency, the absorption of dusty plasma on EM wave will reduce.

This study aims to introduce a simple equivalent circuit model of circular loop shaped frequency selective surface (FSS), predicting the plane-wave transmission characteristics for oblique angles of incidence. The equivalent circuit model is based on a series of basic equations in order to calculate the inductance and capacitance of strip gratings. Through provided relations, the values of circuit elements can be calculated as well. The proposed relations are applied to many circular loop FSSs with different dimensions, and the results are compared with the full-wave simulations obtained from computer simulation technology microwave studio. Moreover, some comparison graphs between the simulated and analytical resonant frequency for different values of design parameters have been carried out to show the circuit model follows the trend of the simulated responses. Finally, both the FSS structures have been fabricated and measured in an anechoic chamber. A good agreement between the experimental results and the simulated responses demonstrates the validity of the circuit model.

In this study, millimetre wave (MMW) voltage controlled oscillator (VCO) is designed using 130 nm complementary metal–oxide–semiconductor single poly eight metals (1P8M) technology. Under 0.8 V supply, VCO can be tuned from 46 to 61.2 GHz, i.e. 28% frequency tuning range (FTR) is achieved. For the highest oscillation frequency, phase noise at 10 MHz offset frequency is −117.3 dBc/Hz, while the power dissipation is 9.39 mW. The FTR is improved by adopting multiband scheme using transformer tuned technique. Improvement in phase noise is done with a P-type metal–oxide–semiconductor as a variable capacitor for fine tuning of each band. Single N-type metal–oxide–semiconductor switch is placed on secondary side of transformer which makes the transformer tunable. Figure of merit of the proposed circuit is −183.3 dBc/Hz. Proposed VCO provides wide FTR and acceptable low phase noise for V-band application.

Directional modulation (DM) has been developed based on narrowband antenna arrays, which can form the desired constellation values in the directions of interest while scrambling the values and simultaneously maintaining a magnitude response as low as possible in other directions. In this study, for the first time, the authors develop a multi-carrier based DM framework using antenna arrays, where simultaneous data transmission over multiple frequencies can be achieved, so that a much higher data rate can be obtained. In addition, such a framework allows possible frequency division based multi-user access to the system and also provides the flexibility of using different modulation schemes at different frequencies. Then, they study the antenna location optimisation problem for multi-carrier based DM using a compressive sensing based approach by employing the group sparsity concept. Examples are provided for both the design of weight coefficients and the optimisation of antenna locations.

The objective of this work is to address the issue of using the human hand as an antenna, the hantenna. The method used is based on an experiment involving a wireless link between a traditional antenna and the human hand functioning as an antenna. Measurements were performed over six subjects in an anechoic chamber. The results show very clear trends. In the frequency band 800 MHz–2 GHz the human hand does improve the link performance, mainly by providing a better matching to the feeding cable. The main conclusion is that expressed in realised gain, the improvement of the link may go up to 15–20 dB, which is very considerable. The significance of the work is that it shows how to use the human hand as an antenna in certain non-critical telecom applications.

A frequency agile Vivaldi antenna whose operating frequency band can be switched between two selected bands is proposed in this study for spectrum monitoring and cognitive radio applications. A radiofrequency (RF) switch is introduced into the back-slot of a Vivaldi antenna to allow switching of the operational band. The realised gains of the antenna are 10.5 dBi in the low band around 3.1 GHz, and 12 dBi in high band around 4.1 GHz. The radiation pattern is stable and its direction is consistent across the two bands. This design can be applied to multiple reconfigurable bands by using more RF switches to tune the desired operating frequency. A set of reliable design equations has been provided as well. This reconfigurable antenna offers improved gain and isolation over multiple, wideband and multiband antennas without increasing the cost and size when compared with those designs reported.

This research proposes a microstrip non-linear ring resonator (MNLRR) as a frequency comb generator. Due to multiple circulations of waves along the ring, they interact with the non-linear components several times; thus, in comparison with a microstrip non-linear transmission line with the same number of non-linear components, the MNLRR achieves a higher harmonic-conversion-efficiency. Furthermore, we distinguish three regimes of multi-tone generation for the proposed MNLRR. In the first regime of operation, generation of harmonics at integer multiples of the excitation frequency is observed. In the second regime, one recognises generation of spectral lines at the resonance frequencies of MNLRR in addition to degenerate four-wave mixing tones. Furthermore, we have shown that integer multiples of these spectral components are also excited. In the third regime, we encounter the generation of frequency components whose frequencies are input-power dependent. According to our measurement results, a higher level of excitation power is required for this regime. Here, the number of components increases while their spacing reduces by growing power level.

In this study, planar dual-layer partially reflective surface, also known as frequency selective surface (FSS), antennas have been presented for 60 GHz band (57.24–65.88 GHz) wireless local area network (WLAN) and wireless personal area network (WPAN) applications. The FSS is excited through a microstrip patch antenna array of two elements designed at 63.72 GHz with return loss (S11) bandwidth and gain of 5.55 GHz and 13.2 dBi, respectively. Both the FSS unit cell and the feeding patch elements are set to be the same and they are designed based on the patch antenna size improvement method to convince the fabrication limitations imposed by the conventional printed circuit board etching process. Then three double layers FSS antennas have been designed with 2-elements, 12-elements and 24-elements in each FSS layer and measured gains of 15.6, 19.1 and 19.75 dBi, respectively, are achieved. It has also been found that when more layers and number of FSS elements are employed to improve the antenna gain, the overall S11 and gain bandwidth is reduced. In all the cases the measured results agreed well with the simulated results.

We present analytical expressions for the evaluation of the antenna efficiency loss due to the gravity distortion on large reflector antennas from 6 to 35 m diameter at X and Ka bands with a lack of usual complexity. These analytical expressions can be used to evaluate the gain reduction versus the maximum deviation of the rim of the reflector due to the gravity distortion extending the model proposed by JPL to other antenna diameter in the range of 6 to 35 m. These expressions were compared with the empirical model for gravity evaluation presented by the Jet Propulsion Laboratory for the DSN antennas obtaining a good match between both models. This is useful to specify the maximum distortion due to the gravity for antenna system design level. For this, a five steps procedure is presented starting with the estimation of the antenna efficiency reduction based on the analytical expressions as a function of the maximum gravity distortion, the antenna size and frequency band and concluding with the estimation of the gain of a single antenna as a function of the elevation angle. The case study is focused on error analyses for large antenna uplink arrays at X and Ka band.

This study proposes a new idea for designing antenna based on graphene for THz application in detailed analysis. Here, design of a novel graphene-based ribbon antenna is presented based on surface plasmon polariton (SPP) behavioural in graphene. Noble metals support and confine EM waves in infrared region. However, SPP wave propagation is supported by graphene in much lower frequencies of infrared region, in THz region. The conductivity of graphene and SPP waves behavioural in graphene sheet is analysed and studied for designing antenna based on new idea of ribbon antenna. The numerical simulations with COMSOL and CST are presented in proposed new idea structure of antenna. In order to achieve the desired tunable THz band communication, the parametric study method is used for the proposed graphene-based ribbon antenna to achieve higher efficiency.

A focused microwave power transmission (MPT) system with high-efficiency rectifying surface is proposed. This work has two main novel contributions: (i) most of wireless power transmission systems reported so far are non-focused. This study presents the first focused MPT system with circular polarisation; (ii) a novel high-efficiency rectifying surface using sub-wavelength resonant elements is developed. To design a focused transmitting array antenna with high power density at the receiving site and high beam collecting efficiency in the near field, a method based on the optimisation of a partial scattering matrix is employed. A left-handed circularly polarised microwave power rectifying surface consisting of 8 × 8 sub-wavelength resonant elements is designed and the measured conversion efficiency reaches 57.74%. To validate the concept, an experimental system including one focused transmitting array antenna and one 2 × 2 elements rectifying surface is implemented and measured, and the improvement of output direct current (DC) power and radiofrequency (RF)-to-DC conversion efficiency compared with non-focused condition is shown. The highest RF-to-DC efficiency of 66.5% is achieved in the focused mode, compared to that of 34.8% only in the non-focused mode as in traditional systems.

Coordinate transformation technique is employed to engineer a metamaterial slab that enables planar wave emission from a planar or line localised source. First a rigorous cylindrical to rectangular coordinate transformation is applied resulting in with a sheet current generating a plane wave with impedance matching at the boundary between the device and the surrounding medium. Then, based on physical reasoning, the material constitutive parameters are further reduced to having only one entry of the spatially varying permeability tensor instead of two entries as discussed in the references. This further reduction is equivalent to modifying the near field in the transformed domain. Finally, due to a specific mu-near-zero condition near the origin, the sheet source is transformed to a localised one in the transformed domain and via full-wave simulations, the authors show that the field is still propagating as a plane wave. Moreover, the transmission line (TL) metamaterial implementation with discretised spatially varying permeability is designed. The capacitor- and inductor-loaded two-dimensional TL grid is used to synthesise the required spatially varying relative permeability in the wavefront converter metamaterial slab. The TL metamaterial design is proven to successfully synthesise a planar wave front using a microwave circuit simulator.

An X-band microstrip antenna array is fully designed. A multilayer structure is chosen for the antenna and the radiating elements are fed by the aperture-coupled patch technique. A mono-pulse feeding network is also designed which distributes the power to the radiating elements in a way that low sidelobe level is created in the sum pattern and both difference patterns. The measurement and simulation results coincide well in the whole bandwidth.

This study presents a fully integrated complementary metal oxide semiconductor (CMOS) power amplifier (PA) covering LTE-advanced bands from 825 to 915 MHz for cellular application and the bands of 978 MHz universal access transceiver mode and 1090 MHz extended squitter mode of an automatic dependent surveillance-broadcast transmitter for the unmanned aircraft system. The 3.63 mm × 0.95 mm PA including all on-chip input and output matching networks, fabricated using the 0.18 μm CMOS process exhibits peak output power of 24 dBm, modulated output power of >22 dBm at 978 MHz, the maximum power gain of 27 dB and bandwidth of 290 MHz.

This study studies the multiple-input–multiple-output (MIMO) performance in a tunnel scenario for the millimetre-wave (mm-wave) band. We simulated and measured channel impulse response at 28 GHz for grids of transmitters and receivers to study the feasibility of mm-wave MIMO system for metro communication in tunnel environment. The ray-tracing method was utilised to obtain the MIMO channel matrices. The performance of the channel is studied in terms of 2 × 2 and 4 × 4 MIMO, and the influences of antenna spacing on the channel capacity are investigated. The results provide a reference for the fifth-generation wireless network in the future communication-based train control system applications.