The 50 most-cited articles in Electronics Letters, 2017

Multi‐Watt high‐power terahertz (THz) frequency quantum cascade lasers are demonstrated, based on a single, epitaxially grown, 24‐μm‐thick active region embedded into a surface‐plasmon waveguide. The devices emit in pulsed mode at a frequency of ∼4.4 THz and have a maximum operating temperature of 132 K. The maximum measurable emitted powers from a single facet are ∼2.4 W at 10 K and ∼1.8 W at 77 K, with no correction being made for the optical collection efficiency of the apparatus, or absorption by the cryostat polyethylene window.

A four‐element dual‐band MIMO configuration consisting of split‐ring resonator (SRR)‐loaded inverted L‐monopole antenna elements is realised. In the proposed antenna, the lower‐frequency mode of the unloaded MIMO configuration merges with one SRR‐induced antenna resonance. This leads to antenna operation around 2.93 GHz with wide impedance bandwidth (IBW) of 35.21%, encompassing the lower WLAN, worldwide interoperability for microwave access, wireless fidelity, fourth generation (4G)‐long‐term evolution and sub‐6 GHz 5G bands. Furthermore, due to SRR loading, the proposed MIMO antenna exhibits a resonance at 5.68 GHz (IBW 6.86%), covering the upper WLAN band. Minimum inter‐element isolation of 14 dB is achieved, in spite of the compact total area ( , λ 0 = highest operating wavelength) and the presence of inter‐connected ground plane. Both the working bands exhibit directional radiation patterns with average gain . Experiments on the fabricated antenna prototype confirm that the simulated and measured S ‐parameters, radiation patterns (envelope‐correlation coefficient, channel…

Feature redundancy‐reduced convolutional neural network (FRR‐CNN) is proposed to address the problem of facial expression recognition. Different from traditional CNN, convolutional kernels of FRR‐CNN is induced to be divergent by presenting a more discriminative mutual difference among feature maps of the same layer, which results in generating less redundant features and yields a more compact representation of an image. Furthermore, the transformation‐invariant pooling strategy is used to extract representative features cross‐transformations. Extensive experiments are conducted on two public facial expression databases and the obtained results demonstrate the efficiency of FRR‐CNN comparing with the state‐of‐the‐art expression recognition methods.

Without doubt, one of the powerful and effective optimiser in the area of evolutionary algorithms and improved particle swarm optimisation (PSO) is the self‐organising hierarchical PSO with time‐varying acceleration coefficients (HPSO‐TVAC) which has been implemented successfully in the many problems (cited by 2430 until now). Real‐world problems are multi‐variable problems with real‐world different complexities. The classical HPSO‐TVAC optimisation technique often converges to local optima solution for some of the real‐world problems. Therefore, finding efficient modern versions of the PSO algorithm (here HPSO‐TVAC) to solve the real‐world problems are absorbing a growing attention in recent years. A novel HPSO‐TVAC algorithm for real‐world optimisation is proposed. The simulation results show that proposed HPSO‐TVAC new version, NHPSO‐JTVAC, is powerful and very competitive for real‐world optimisation.

The problem of direction of arrival (DOA) estimation with co‐prime linear arrays is researched. An improved DOA estimation algorithm based on root‐multiple signal classification (MUSIC) is proposed. The method can solve the matching error problem in Sun's algorithm. In addition, it can make full use of signal space and noise space to improve the estimation accuracy with low complexity. Experimental results verify the validity of the proposed algorithm.

A novel Zeonex based porous fibre is proposed for biomedical imaging and polarisation preserving applications of terahertz waves. The standard finite element method is used to simulate the propagation characteristics of the fibre that shows high numerical aperture of 0.48, high birefringence of 0.039 and a flattened dispersion of 1.07 ± 0.05 ps/THz/cm. In addition, the fibre also possesses low effective material loss and negligible confinement loss in the terahertz frequency band.

In this Letter, a mu‐negative metamaterial (MTM) filter‐based novel decoupling technique is presented for multiple input multiple output (MIMO) antennas. The design process has been described in a systematic manner, starting with the basic two port monopole antenna and then adding cancellation network and finally the proposed MIMO antenna by adding the matching network. Since the presented decoupling network is developed using MTM structure, good isolation between the antennas is achieved by maintaining compactness. The presented isolation technique can be used in different applications like in developing circularly polarized and multi‐band MIMO antennas. As an example, two port circularly polarised MIMO antenna design is also presented. The proposed designs have been fabricated and the simulation results are experimentally verified.

A novel and effective speech enhancement method is proposed for suppressing the white noise as well as non‐stationary acoustic noises. The proposed method employs the combination of variational mode decomposition (VMD) and empirical mode decomposition (EMD) methods. In this method, first EMD is used to decompose the noisy speech signal into intrinsic mode functions (IMFs). Further, the VMD is applied on summation of selected IMFs. The main contribution of the proposed method is the selection of IMFs based on Hurst exponent and further applying steps of VMD method. The proposed modified EMD‐VMD (mEMD‐VMD) method is suitable to reduce the low‐frequency noise as well as high‐frequency noise. The proposed method gives the better results in terms of speech quality and composite measures. The proposed study is performed on eight speech signals under additive white Gaussian noise, street noise, babble noise, and airport noise taken from NOIZEUS database.

This Letter reports the finding of a point‐cycle chaotic bursting phenomenon in a simple third‐order memristive diode bridge‐coupled Sallen‐Key lowpass filter (LPF). By parallel coupling a generalised memristor composed of a diode bridge and an inductor into a Sallen‐Key LPF a simple third‐order memristive chaotic oscillator is established. With the modelling of this oscillator, stability analyses, numerical simulations and hardware experiments are performed, upon which the striking point‐cycle chaotic bursting phenomenon is well demonstrated and effectively validated.

Two ground radiation antennas with polarisation diversity performance were proposed for MIMO WLAN applications in wearable devices. The antennas can simultaneously excite the vertical mode and horizontal mode of the ground plane and the phase difference between the two modes can be controlled by utilising an inductor‐loaded metal strip in the ground plane, generating circular polarisation. A 3:1 VSWR bandwidth of 140 MHz with high isolation (above 17 dB) and a 3 dB axial ratio bandwidth of 100 MHz was obtained. The opposite rotations generated by the two antennas resulted in good diversity performance, which was verified by the measured envelope correlation coefficient.

A mutual coupling reduction antenna design for WLAN MIMO application is proposed. The proposed antenna array consists of two rectangular patch antennas, six parallel metal strips, a single substrate layer, and common ground plane. About −42 dB mutual coupling is achieved at the 5.8 GHz resonant frequency. Both simulation and measurement results confirm improvements in mutual coupling at about 30 dB when compared with those without metal strips. The radiation patterns are almost unaffected by adding these metal strips in the proposed antenna.

For the first time, 3D printed metal‐pipe rectangular waveguides (MPRWGs) have been demonstrated in the WM‐380 (500–750 GHz) and WM‐250 (750 GHz–1.1 THz) waveguide bands. The ultra‐high spatial resolution offered by the new RECILS additive manufacturing technology enables the precision fabrication of these prototype MPRWGs at such high frequencies. This enabling technology avoids the need for access to expensive microfabrication resources and, thus, opens up the terahertz spectrum to the low‐cost manufacture of passive components.

Advances in wireless sensor technologies and MEMS have made it possible to automatically monitor the health status of dairy cows using Internet of things (IoT) and wireless body area networks. Since on‐cow measuring devices are energy constrained, a proper characterisation of the off‐body wireless channel between the on‐cow sensor nodes and the back‐end base station is required for an optimised deployment of these networks in barns. In this Letter, the long range (LoRa) off‐body wireless channel has been characterised at 868 MHz, a typical IoT frequency. Both path loss and temporal fading were investigated using LoRa motes. Based on this characterisation, network planning and energy consumption optimisation of the on‐body nodes could be performed, which enables the deployment of reliable dairy cow monitoring systems.

A novel dual‐band substrate integrated waveguide (SIW) bandpass filter (BPF) based on complementary split‐ring resonators (CSRRs) is proposed. It consists of an SIW dual‐mode cavity loaded by two additional CSRRs on its top layer. Both TE 102 and TE 201 modes in the cavity can be excited by the proper positions of the feeding lines. Two additional CSRRs are etched on the top layer coupled with the TE 102 and TE 201 modes, respectively, to achieve the dual‐frequency operation. Four transmission zeros are generated in the vicinity of the passbands to improve the selectivity. To validate the design concept, a dual‐band SIW BPF operating at 7.89 and 8.89 GHz is designed, simulated and measured. The measured results are in good agreement with the simulations.

A novel circuit is presented for the design of transmission‐type negative group delay circuit (NGDC) with low signal attenuation. By loading a lumped resistor at a specific point on the loose‐coupling microstrip (MS) resonator, a lossy coupled‐line resonator is proposed, the size of which is effectively reduced by employing an open radial patch. A cascaded two‐stage NGDC scheme is presented to realise an enhanced negative group delay (NGD) value and better reflection coefficients. The layout of the two‐stage NGDC is designed in an anti‐symmetrical back‐to‐back manner. To validate the performance of the proposed circuit scheme, a prototype of the two‐stage NGDC has been designed, the working bandwidth of which is 35 MHz with a centre frequency of 1.79 GHz. This circuit is fabricated on Rogers RO4350B substrate with a thickness of 20 mil. A measured maximum NGD of −7.7 ns and a corresponding signal attenuation of as low as 8.6 dB have been obtained. Reflection coefficients are better than −20 dB. This NGDC occupies a compact size of 0.3 λ g × 0.18 λ g , which is much smaller compared…

A new license plate detection method for challenging environments is proposed. Background clutters are common in road scene images and the detection of license plates (occupying only a small part of an image) is considered as a difficult problem. In order to address this problem, a two‐step approach is developed: first vehicle regions are detected and the license plate in each vehicle region is localised. This vehicle region detection based approach provides scale information and limits search ranges in license plate detection, so that one can reliably detect license plate regions. To be precise, the faster region‐based convolutional neural network algorithm for the vehicle region detection is adopted and candidates for license plates in each detected region with the hierarchical sampling method are generated. Finally, non‐plate candidates are filtered out by training a deep convolutional neural network. The proposed method is evaluated on the Caltech dataset and the method showed a precision of 98.39% and a recall of 96.83%, which outperforms conventional methods.

Although action recognition is a widely studied field in computer vision, the recognitions of aggressive activities and crowd violence actions are comparatively less studied. Nowadays, so many surveillance cameras have been installed in the streets and there is a demand for intelligent crowd activity detection systems. A method for violence detection in videos is proposed. The primary contribution is a novel transfer learning‐based violence detector that gives promising results compared with the existing detectors. First, the optical flows of the input videos are computed via Lucas–Kanade method. Then, several 2D templates are constructed with overlapping optical flow magnitudes and orientations. These templates are supplied to a pre‐trained convolutional neural network as input and deep features of different layers are extracted. Cubic kernel support vector machine and subspace k ‐nearest neighbours classifiers are trained for prediction and the proposed method is tested with three different datasets that commonly used in violence detection studies.

To improve the availability of the software‐defined networking (SDN) under distributed denial of service (DDoS) attacks, a multi‐queue SDN controller scheduling algorithm based on time slice allocation strategy is proposed. The proposed algorithm can take different time slice allocation strategies according to the intensity of DDoS attacks and use SDN controller to schedule processing flow request from different switches (including the switches suffering from different degrees of attacks and normal switches) to ensure better protection to the normal switch in the network under DDoS attacks. Simulation results are presented to show the effectiveness of the proposed algorithm.

A new approach to suppress mutual coupling of spatial electromagnetic fields between two circularly polarised (CP) antennas using frequency selective surface (FSS) technique around 30 GHz is presented. The transmission‐type FSS layer with the CP capability is placed on the top of two closely multiple‐input, multiple‐output (MIMO) antennas. The study shows that the FSS layer can suppress an average of 10 dB mutual coupling between two adjacent CP‐MIMO antennas. The proposed technique does not degrade the impedance and radiation performance of the antenna in comparison with the antenna without FSS layer. The two‐port CP antennas are fabricated and measured to validate the simulation results. Good agreement is achieved between simulated and measured results in terms of the reflection coefficient, mutual coupling, and axial ratio.

This Letter presents a design of microstrip filtering power divider for dual‐band application. The proposed dual‐band filtering power divider is based on the traditional Wilkinson power divider and employs T‐junction structures and quarter‐wavelength stepped impedance resonators (SIRs) to realise dual‐band power allocation and bandpass response simultaneously. The design process is simple and effective. For validation, a dual‐band microstrip filtering power divider with centre frequencies of 0.9 and 2.1 GHz for the GSM and WCDMA applications is designed, fabricated and measured. The measured results indicate that the proposed dual‐band filtering power divider showcases low‐loss characteristics, high isolation as well as good selectivity.

A substantial reduction of substrate integrated waveguide (SIW) insertion loss can be achieved through the use of air as dielectric instead of usual dielectric material. However, air‐filled SIW (AFSIW) circuits exhibit larger footprint compared with their dielectric‐filled counterparts. A compact multilayer AFSIW bandpass filter is proposed to realise both high‐performance and small footprint. For demonstration purpose, a Ka‐band multilayer fourth‐order AFSIW bandpass filter has been designed and fabricated. Measured and simulated results are in good agreement. Retro‐simulations, taking into account fabrication tolerances, are also presented. Finally, a performance comparison with other multilayer technologies is presented.

The fabrication and analysis of a flexible and stretchable 3D printed passive ultra‐high frequency (UHF) radio‐frequency identification (RFID) tag are presented. The tag is fabricated on a flexible 3D printed Ninjaflex substrate and the conductive part of the tag consists of stretchable silver conductive paste dispensed with direct write method. The details of the 3D printing of the substrate, the characterisation of the substrate material at the UHF band, the direct write dispensing of the tag antenna, and the simulation and wireless measurement results of the fabricated tag are outlined. Moreover, to verify the flexibility and stretchability of the tag, strain reliability results of the tag are presented. Measurement results show that initially the manufactured tag achieves a 10.6 m read range. After 100 times of harsh stretching, the read range is still 7.4 m. Overall, the performance of the tag is robust and concludes that the fabrication methodology can be used in the manufacturing of RFID tags for future identification and sensing applications.

The exact blood vessel trees segmented from fundus images provide important information required for screening and following‐up of diabetic retinopathy and age‐related macular degeneration. The trained deep neural network presents an automated prediction of the blood vessels in retinal fundus camera images in the publicly DRIVE database with accuracy up to 0.9533 and area under the receiver operating characteristic curve up to 0.9752, which is better than manual recognition by expert human eyes. A resizing technique is introduced and applied to the multi‐level network combining dropout and spatial‐dropout layers to obtain more generalised training. The proposed model has the potential for the classification of other types of images.

A compact filtering power divider composed of two quarter‐mode circular cavities based on the substrate integrated waveguide is proposed. Two extra perturbing via‐holes added in each side of the quarter‐mode circular cavity achieve a selective bandpass filtering response and improve the performance of the upper stopband. The proposed FPD operates at 9.1 GHz with a 3 dB fractional bandwidth of 19.8%. The insertion loss in operating band is < 1.6 dB and the input return loss is better than 16 dB. The amplitude and phase imbalances between the two outputs are measured better than 0.6 dB and 3.5°, respectively. The measured results exhibit good agreement with the simulated ones.

A compact seventh‐order wideband bandpass filter (BPF) with sharp roll‐off skirts using coupled lines and open stubs (OSs)/shorted stubs (SSs) is proposed. Seven transmission poles in the passband and four deep transmission zeros from 0 to 2 f 0 ( f 0 denotes centre frequency of the passband) can be realised with the help of half‐wavelength OSs and quarter‐wavelength SSs. For demonstration, a wideband BPF prototype is designed, fabricated with a measured 3‐dB fractional bandwidth of 78% (1.22–2.77 GHz) and transition band roll‐off rates of over 175 dB/GHz. Good agreement between the simulations and measurements validates the design method.

A shared aperture metasurface (SA‐MS) is proposed to achieve the wideband radar cross‐section (RCS) reduction and gain enhancement of a circularly polarised (CP) microstrip antenna simultaneously. The SA‐MS is composed of a wideband polarisation conversion surface and a partially reflecting surface (PRS). A 180° phase difference can be obtained by the polarisation conversion surface, which results in a wideband RCS reduction in normal incident direction. The Fabry–Perot resonator cavity is constructed by the PRS and the metallic ground of the CP microstrip antenna to enhance the gain. Experimental results show that the gain enhancement reaches 1.15 dB around the operating band and a wideband RCS reduction is obtained in the frequency range of 9–17 GHz, in which the average RCS reduction is 10.9 and 10.68 dB for dual polarisation in the normal incident direction.

A planar U‐shaped resonator for measuring relative permittivity of the liquid mediums is developed. To improve the sensitivity of the proposed sensor, gap sections, coupled lines and central ring resonators (RRs) are used to enhance electric fields interact with liquid under test (LUT). Further to increase the resonance sharpness, a tapered double‐sided spiral split RR is presented. As the permittivity of the LUT is increased from 26 to 79, the measured resonance frequency of the described sensor is varied in the 166.4–287.5 MHz range. The developed sensor exhibits an improvement in sensitivity of about 45% compared with the other work.

A transient control for a dual‐active‐bridge (DAB) dc/dc converter to realise power adjustment in a fast and smooth way is proposed. The converter is able to transfer power between two dc sources with two phase‐shifts as control variables. To eliminate the possible high‐current overshoot and non‐zero dc‐bias current, the adjustments of the two phase‐shifts are distributed to the gating signals of different switch arms according to a ratio x , which has an universal expression for any transitions among different operation modes in a DAB converter. Experimental results have proved the validity of the proposed transient control in elimination of current overshoot and dc‐bias current.

A novel wireless dry EEG brain‐controlled wheelchair with five steering behaviours is devised, which is based on two‐stage control strategies combining sustained and brief motor imagery brain–computer interfaces (SB‐MI‐BCIs). Compared with the existing single modal brain–computer interface (S‐BCI) controlled wheelchair, this new wheelchair has achieved more control commands and higher information transfer rate. Compared with their previous hybrid BCIs controlled wheelchair, subjects can control the wheelchair spontaneously and efficiently just by imagining the left hand, the right hand or both hands without any other visual attentions (e.g. P300 or SSVEP). The experimental results demonstrate that the SB‐MI‐BCIs can efficiently provide multiple independent control signals for wheelchair navigation.

A novel sixteenth‐mode substrate integrated waveguide (SMSIW) bandpass filter loaded with complementary split‐ring resonator (CSRR) is proposed. The filter size is reduced by introducing the SMSIW circular cavity loaded with CSRR. The SMSIW occupies only 6.25% of the conventional substrate integrated waveguide with same resonant frequency. Further miniaturisation is achieved by loading the SMSIW circular cavities with CSRRs. The designed filter is centred at 2.45 GHz with a bandwidth of 8.2%. The measured minimum insertion loss is 0.9 dB and passband return loss is below 10 dB. Good agreement is achieved between simulated and measured results.

The realisation of a fully vertical gallium nitride (GaN)‐on‐silicon (Si) Schottky barrier diode (SBD) without using wafer bonding and Si substrate removal process is reported. The SBD presented a turn‐on voltage of 0.69 V at 1 A/cm 2 , breakdown voltage of 148 V with a specific on‐resistance of 13.9 mΩ cm 2 . The ideality factor and Schottky barrier height were 1.35 and 0.71 eV, respectively. An effective critical electric field was estimated to be 1.48 MV/cm. The Baliga's figure of merit for the SBD was calculated to be 1.57 MW/cm 2 . These results indicate the great potential of GaN‐on‐Si in achieving cost‐effective fully vertical power device.

An ultra‐low power dynamic comparator is proposed with low dynamic offset variation for successive approximation register (SAR) analogue‐to‐digital converter (ADC). Dynamic offset can be cancelled with the cascode current source. Moreover, the power consumption can be reduced because it has no power consumption during the reset phase. With body‐driven technology and cross‐coupled inverter, the positive feedback during the regeneration is enhanced, which reduces remarkably delay time. Simulation results in a 0.18 μm CMOS technology confirm the performance of the proposed comparator. It is shown that the fluctuation of the total offset voltage (mean + 3std) is 0.15 and 0.39 mV with common‐mode voltage from 0.5 V DD to V DD at supply 1.2 and 0.6 V through Monte Carlo simulation, respectively. Furthermore, the delay of the proposed structure can be decreased to 1.837 and 118.2 ns at supply voltages of 1.2 and 0.6 V, while the power consumption is only 18.6 μW and 144 nW, respectively.

A wideband dual‐circularly polarised (CP) substrate integrated waveguide (SIW) cavity‐backed patch antenna is designed by using two‐layer structure. The realised dual‐CP, a cavity‐backed square patch lies on the top substrate is excited by two pins, which are symmetrically located at an offset to the diagonal axis of the patch. These pins induce strong loading effect in the cavity and generate additional resonances in the vicinity of the patch resonant that help to achieve a wideband response by adjusting their locations. Thus, generation of dual‐CP and wide impedance bandwidth is accomplished by using this new feeding topology. Moreover, the antenna is fabricated and tested for dual‐CP. The experimental results show an impedance bandwidth of nearly 28.4% (8.59–11.43 GHz) and an axial‐ratio bandwidth of 3.4% under the criterion <3‐dB.

In this Letter, a flat terahertz (THz) transmit array with a two‐layer element is investigated. The proposed element can provide 360° phase coverage with a transmission coefficient better than −3.52 dB at 250 GHz. Then a transmit array based on the element is designed with a low focal‐to‐diameter ratio of 0.3. Simulation results reveal that the transmit array has large backward radiation. A WR‐03 open‐ended waveguide with a thick wall is used to feed the transmit array, thus the backward radiation is further reflected to the forward direction and the gain is increased by 1.7 dB at 250 GHz. Then the transmit array is fabricated using standard, low‐cost PCB technology, and the measured results show that a peak gain of 28.8 dBi with an aperture efficiency of 32% is achieved. In general, the proposed transmit array has simple structures and can be fabricated by standard PCB technologies which are suitable for applications in low‐cost THz systems.

The impact of receiver's tilted angle on the channel capacity in visible light communications (VLCs) is investigated. First, the system model is analysed. On the basis of the system model, the lower and upper bounds on the channel capacity for the VLC are presented. An optimisation problem is formulated to improve the channel capacity by tilting the receiver plane. The proposed problem is shown to be a convex optimisation problem, which is efficiently solved by using the CVX toolbox for MATLAB. Numerical results show that the channel capacity can be dramatically improved by tilting the receiver plane properly.

This Letter investigates multi‐controller placement problem for software‐defined network aiming at minimising the propagation latency between switches and associated controllers. Distinct from the standard clustering‐based partition approaches, a modified exemplar‐based clustering method based on affinity propagation is presented to address the problem. Instead of specifying beforehand the number and locations of controllers, this method can learn the optimal number and locations of controllers adaptively according to network topology. Extensive simulation results demonstrate that the proposed method can provide more stable and accurate controller placement results in terms of latency minimisation compared with k‐median and k‐centre methods.

A novel frequency selective surface (FSS) exploiting 2.5D miniaturised hexagonal rings (2.5D MHR) is proposed. It can obtain an ultra‐wide stopband and an improved polarisation‐independent property due to the compact hexagon arrangement of 2.5D MHRs. The −10 dB bandwidth of the proposed FSS is from 1.97 to 8.08 GHz, and the deviation of resonant frequencies at 30° under transverse electric/transverse magnetic polarisations is merely 0.006 f 0 . A prototype of the proposed FSS is fabricated and measured to validate the good consistency between simulations and measurements.

A single‐feed circularly polarised (CP) patch antenna loaded with a single dielectric superstrate for a wideband high‐gain CP radiation is presented. Along with the gain enhancement, the emphasis is on extra CP radiation of the antenna caused by the superstrate, which broadens the axial‐ratio (AR) bandwidth significantly. A prototype antenna was fabricated and measured at a frequency of 11 GHz. The antenna with overall size of 40 × 40 × 17.45 mm has a voltage standing wave ratio <2 bandwidth of 24.35% (10.1–12.9 GHz), a 3 dB AR bandwidth of 13.6% (10.3–11.8 GHz), a peak gain of 13.17 dBic, a 3 dB gain bandwidth of >26% (10.0–13.0 GHz), and a radiation efficiency of >90%. The presence of superstrate produces a ∼350% increase in 3 dB AR bandwidth and a ∼7 dB increase in the broadside gain relative to the conventional CP patch antenna.

Digital‐to‐time converters are one of the main building blocks in time‐domain signal processing. The jitter‐power product is analysed and shown to scale up linearly as the full‐scale delay range in current‐mode logic implementations, and quadratically in CMOS logic. It is also shown that CMOS converters outperforms current‐mode ones only when their output range is lower than about 1.4 times the clock period.

In disaster recovery, ground network consisting of mobile terminals of rescue vehicles and civilians may be disconnected due to severe environment. In this situation, multiple unmanned aerial vehicles (UAVs) form an aerial network to enhance the connectivity of the ground network. When two nodes in ground network are disconnected, they adopt UAVs as relays to transmit data. Otherwise, they communicate with device‐to‐device manner. With this framework, the coverage probability of these two kinds of users is analysed. Besides, the optimal altitude of UAVs to maximise the capacity of ground network is achieved. A guideline is provided for the design of multiple UAVs support wireless network.

A low complexity multiple signal classification (MUSIC)‐based angle estimation method in monostatic multiple‐input multiple‐output (MIMO) radar has been proposed. To reduce the computational burden and maintain the accuracy of solution, the beam‐space reduced‐complexity MUISC algorithm is developed for monostatic MIMO radar. As the results, the lower computational cost and higher angle resolution in pseudo spectral domain have been obtained. Some simulation results have been given to show the effectiveness of the proposed method.

The first substrate integrated waveguide dual‐band bandpass filter with wide‐stopband performance is presented. This filter is synthesised and designed with fourth‐order Chebyshev responses and identical fractional bandwidths for the two passbands centred at 12 and 16 GHz. Multiple spurious resonances have been intrinsically suppressed by introducing the harmonics‐staggered technique and the centred coupling windows. Good agreements can be observed between the measured and simulated results, and better than 25‐dB rejection level up to 2.05 f 1 has been successfully achieved.

This Letter proposes a circularly polarised (CP) monopole antenna with filtering function, which is achieved by integrating a miniaturised coupled filter based on the bent‐loop resonators. The circular‐polarisation is obtained by using the falcate‐shaped patch as the radiation part, and the existence of the coupled filter in the feeding line would not affect the CP radiation performances. Both numerical simulation and experimental demonstration are performed for the designed CP filtering antenna, and good agreements are obtained. The designed antenna with dimension of 70 × 75 mm 2 exhibits good frequency selective performances for the return loss, gain and axial ratio at 2.45 GHz with measured impedance matching bandwidth (| S 11 | < 10 dB) of 0.23 GHz. Such CP filtering antenna is a good candidate for the emerging application area, e.g. wearable biotelemetric devices.

‘Internet of things’ (IoT) operates for all‐time availability of network components to provide a wide range of service applications to the network users or clients. IoT operates for a large number of applications, and one of these include the sensor deployment for data support to clients. However, these sensors require a large number of queries to be handled by the network components considering the constraints of memory, energy, and delays. These issues can be easily tackled by deploying unmanned aerial vehicles (UAVs), which serve as dynamic nodes to handle clients’ queries by acting as on‐demand gateways. However, this UAV‐assisted IoT requires efficient localisation to determine the sensor for handling multiple‐content queries, which is considered as a problem. A cost function is formed in the proposed approach to generate an optimisation problem which is resolved using a radial basis function kernel support vector machine. The effectiveness of the proposed approach is demonstrated in terms of significant gains attained in terms of error in the cost function, overheads in…

A microstrip lowpass filter (LPF) with ultra‐wide stopband suppression and compact size based on dual‐plane structure is presented. The LPF is composed of high‐impedance resonators loaded by folded patches on the topside plane, combined with hybrid slot and step‐impedance resonators on the ground plane. Multiple transmission zeros are created in the stopband region by different resonators. Thus, an ultra‐wide stopband with 11th‐harmonic suppression is achieved. A demonstration filter with 3 dB cutoff frequency ( f c ) at 2.45 GHz has been designed, fabricated and measured. Results show that the relative stopband bandwidth is 163.8% with attenuation level of 20 dB. The insertion loss is lower than 0.3 dB and the return loss is better than 17 dB in the passband. The size of the LPF is only 8.90 mm × 8.93 mm, which corresponds to 0.115 λ g × 0.116 λ g ( λ g is the guided wavelength at f c ).

A novel capsule antenna with dual‐band performance and small occupation of inner capsule space is proposed. The antenna is designed by combining rigid Rogers substrate with flexible polyimide, which takes full utilisation of capsule inner surface and the system ground for implanted electronics. The antenna structure is based on two identical orthogonal strips, each connected with one conformal L‐strip. In addition, a shorting pin is introduced, bringing in a fundamental resonance at 1.4 GHz industrial, scientific and medical (ISM) band with linear polarisation. Besides, with the adoption of the shorting pin, two extra resonant modes are excited and split in higher band, generating two orthogonal electric fields with equal amplitude and π /2 phase difference; therefore, covering another ISM band at 2.45 GHz with circular polarisation property. Finally, the simulation results show a wide impedance bandwidth of 16.2% at 1.4 GHz ISM band (for | S 11 | <−10 dB), and a broad axial ratio (AR) bandwidth of 34.8% at 2.45 GHz ISM band (for | S 11 | < −10 dB and AR <3 dB), with dual‐band…

An n ‐pole absorptive reciprocal filter consists of at least 2 n single‐mode resonators is proved. An absorptive band‐pass filter with four‐pole Chebyshev response is designed with two four‐pole filters and two‐quadrature hybrids. The quadrature hybrids are used to divide the signals into two paths. Additional two ports are introduced to absorb the reflected energy. This circuit structure is easy in fabrication on superconducting wafers. The filter is successfully designed and fabricated on an MgO substrate. The measured results match well with the simulations.

Operation of single‐stage, single‐pump E‐band bismuth‐doped fibre amplifier with gain, noise figure and efficiency comparable to the state‐of‐the‐art erbium‐doped fibre amplifier of the same complexity and the gain bandwidth of 50 nm is demonstrated. The amplification of 10 Gbit/s intensity modulation/direct detection signal with power penalty below 1.5 dB is reported.

Quantum logic gates are the building blocks of quantum computer. Here in this Letter the authors propose a new technique of implementing quantum square root of NOT gate by phase encoding mechanism.

An air‐filled substrate integrated waveguide (AFSIW) slot array antenna based on multilayer PCB process is proposed. For comparison and demonstration purposes, 1 × 4 slot array antennas based on both AFSIW and conventional dielectric‐filled SIW (DFSIW) operating at 30.5 GHz are designed, fabricated and measured. The exampled AFSIW 1 × 4 slot array antenna achieves 44 and 18% narrower measured H‐plane and E‐plane half‐power beamwidth, respectively, and simulated radiation efficiency improved by 1.6%, resulting in an overall measured gain improvement of 3.5 dB compared with its DFSIW counterpart. This antenna is of high interest for the design of efficient arrays based on high‐performance AFSIW feeding network.